The Frontal Lobe

Within the cerebral cortex, one of the four lobes is called the Frontal lobe.

Anatomy

This lobe is located at the ‘Front; of the brain (the clues in the title!).

Separated by the Central Sulcus (CS), from the Parietal lobe and the Lateral Sulcus (LS) from the Temporal lobe.

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Image: adapted from Pixabay

This lobe consists of a variety of roles, further separated into 3 sections:

The Motor Cortex 

  • Primary Motor Cortex (1)
  • Premotor & Supplementary Motor area (2)

The Prefrontal Cortex (At the very front of the frontal lobe) (3)

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Image: adapted from Pixabay

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Function

The Primary motor Cortex

The primary job of the motor cortex is controlling voluntary movement.

Imagine making a cup of tea. Whilst the activity seems simple, it is actually quite a complex process with a series of steps:

  1. Firstly, fill a kettle with water
  2. Turn the kettle on
  3. Wait for water to boil
  4. Pour water into mug with a teabag in
  5. Stir
  6. Add milk and sugar to taste

Something that seems so simple, requires a great deal of dedication from the brain to avoid scolding ourselves with hot water or worse, ruining a perfectly good cup of tea!

Dr. Penfield stimulated different areas of the Motor cortex to see just how dedicated it was to what part of the body and what movements. This produced a similar somatotopic map to the somatorsensory cortex; showing areas aren’t proportional to their size but the complexity of movements that they perform.

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Image source: antranik.org

The motor cortex requires information to be fed in and out of it. This is where the Premotor and Supplementary Motor areas get involved, which are in charge of the “intention to act”. This combines motor planning information, selecting appropriate movement for the task, with information from the bodily senses via the somatosensory cortex.

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Once done, the information is fed out; back to the somatosensory cortex and to the spinal cord, to perform muscle movements. (But don’t forget, the left and right cross over between hemispheres and body!)

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Finally, let’s look at where all this sensory and motor information comes together: The Prefrontal cortex.

If we left the information to do as it pleased with no conscious control, who knows what would happen; undoubtedly mayhem. This is where the Prefrontal cortex takes over using:

  1. Attention
  2. Decision making and
  3. Coordination

…allowing us to achieve our goals. Whether that’s something small like making that cup of tea to turning up to your lecture on time.

To do this, the area needs to exert top-down processing on various other brain areas, including the sensory and motor (as well as subcortical) areas; which requires connections between them.

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The prefrontal cortex therefore selects task relevant information and inhibits task irrelevant information. (Remember, Inhibits = Irrelevant!)

For example:

  • When making a cup of tea, we want to pour the water in the cup, not on our hand.
  • When attending a lecture, we want to get out of bed, get ready and walk to University and don’t want to watch Netflix all day.

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Alongside this, the Prefrontal cortex is dedicated to a number of other roles including…

  • Executive function (involving attention, working memory and problem solving)
  • Emotion and decision making

All these, psychologists have spent testing using behavioural tests including the Stroop Task, N-back task, the Tower of London and the Iowa Gambling task.

Now after all this learning, shall we go put the kettle on?

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Words and images: Ellen Akehurst – Blogger

Edited: Hannah Slack – Director

 

 

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Emotion and the brain

What are emotions?

Think about how you would define ‘happiness’ and ‘sadness’.

We all know how it FEELS like to be happy or sad, but putting it into words is quite complicated.

Emotions are difficult to define and are amongst the most debated topics in psychology. In this blog pos,t you’ll find some of the most important basic information that regard the topic of emotions.

Why do we have emotions?  

Well, emotions are very important for our survival; fear, for example, helps you to make fight or flight responses when in a dangerous situation.

Emotions are also important for reproduction (love) and upbringing (attachment).

Emotions help us to make quick decisions in response to complex problems through avoidance or approach learning.

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EXAMPLE: There’s a spider in your living room.

What do you do:
a- pick the spider up and let it free
b- scream and hide in your room until your housemate comes home

I know which I would do.

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The components of emotion

Two main components of emotions have been identified: emotional response and subjective feeling of emotion.

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Just in case you went to the pub tonight and someone happened to ask you about emotions, here’s a summary of everything you should be able to talk about after this blog post:

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Emotional response

Let’s look at the emotional response component first.

An emotional response features:

  • changes in the autonomic nervous system
  • hormonal changes
  • typical actions

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Changes in the autonomic nervous system

The Autonomic Nervous System (ANS) is composed of the:

  • PARASYMPATHETIC nerves (used for functions related to ‘rest and digest’)
  • SYMPATHETIC nerves (Used for ‘fight or flight’).

The two systems are mutually exclusive: when one is active, the other is not.

The sympathetic nervous system

In particular, the sympathetic nervous system is used for short term emergencies: fear, anger and sexual arousal (#totalemergency).

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It works by initiating a series of physiological response which help coping with the emergency: it increases heart rate, slows digestive functions, increases perspiration, increases glucose availability.

The parasympathetic nervous system

Whereas, the parasympathetic nervous system has the opposite purpose. This is you at rest – when there’s a emergency situation. you aren’t angry or scared – all is chill. It includes:

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You have no voluntary control over your autonomic nervous system as it’s all controlled by your hypothalamus (remember that guy?).

Applications

Changes in the autonomic nervous system can be used in:

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  • lie detectors (polygraphs, if you’re talking fancy)
  • recording skin conductance response (used for research purposes – they record how much you sweat…eww!)

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Hormonal changes

Quick reminder of how hormones are released:

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The main hormones involved in emotional responses are produced by the adrenal glands (located on top of the kidneys, from the latin ad= on top, ren= kidney).

The hypothalamus releases a releasing factor that in turn then tells the pituitary gland to release its releasing factor (called ACTH) that then tells the adrenal glands to release the hormones into the blood.

The most common hormones produced are cortisol (the stress hormone) adrenaline, and noradrenaline.

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It’s like when you order an item online. The hypothalamus is the computer that decides which item (hormone) is needed. The computer then send a message to the business owner (the pituitary gland). The business owner then sends a message to the warehouse (adrenal gland) to dispatch the item (release the hormones).

The hormones released by the adrenal gland are:

  • cortisol (the chemical associated with stress)
  • adrenaline (known as epinephrine by the americans)
  • noradrenaline (known as norepinephrine by the americans)

When you get stressed, the production of these hormones increases.

The purpose of this is to increase the amount of glucose and oxygen that is given to the muscles and brain (ready for you to fight or run away).

This is also why being stressed last for an extended period of time – the hormones associated with stress are released into the blood and thus, last for a longer time in the body.

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Typical actions

Some actions are typical of certain emotions; for example, body postures of flight/fight in the presence of a threatening stimulus.

Facial expressions are also quite informative of someone’s emotions. This can refer to how you hold your body and what gestures you use:

Paul Ekmann (1955) identified 6 basic emotions (happiness, sadness, fear, anger, surprise, disgust) that can be found across cultures, even in the most remote tribes of the Amazon- how cool is that.

If you’re struggling to remember these, think of the emotions from the Disney Pixar movie, Inside Out – only their cousin, Surprise, came to visit.

If you are interested in this topic, ‘Lie to me’ is a great TV show.

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So, how are facial expressions produced?

Facial expressions can either be voluntary or involuntary, and the neural systems underlying the two are different.

Voluntary facial expressions are elicited from the corticospinal system inputting to the pyramidal tract, in the motor cortex.

Involuntary facial expressions (spontaneous) are elicited by the subcortical system inputting to the extrapyramidal tract (insula and basal ganglia).

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Emotions as subjective feelings

How do we get to the point in which we are aware of our emotions?

How do you distinguish the emotion underlying either crying because your partner broke up with you or crying because you’ve just seen a video of a cute puppy?

The researcher Antonio Damasio theorised that the awareness of emotions results from integrating external events and the physiological responses.

We’ve seen how emotions are composed by both emotional responses and subjective feelings, but what comes first? There are two main theories that attempt to investigate this: the James-Lange theory (1884) and the Cannon-Bard theory (1927)

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The James-Lange theory of emotions

The James-Lange theory posits that, after exposure to an emotional stimulus, the physiological changes elicited send information from the spinal cord to the brain giving rise to a specific emotion.
For example, seeing a huge hairy spider/a scary bear, will elicit physiological responses (i.e. increased heart rate, increased glucose availability, goose bumps…) and, after the information has been passed to the brain, you’ll experience fear (if those things actually scare you, duh).

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The main thing to grasp with the James-Lange theory is they believe that it goes:

Body sensations first -> then brain produces the subjective feeling

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Criticisms:

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This theory however does not take into consideration that the autonomic responses are fairly crude and not differentiated enough to account for the whole range of emotions we can feel.

Moreover, patients with spinal cord injury can still feel emotions, which would not be expected if the James-Lange theory was accurate.Screen Shot 2016-06-07 at 22.31.14

The Cannon-Bard theory of emotions

The Cannon-Bard theory posits that, after exposure to an emotional stimulus, the appropriate emotion is elicited; information goes from the brain to the spinal cord and elicits physiological changes.

If you saw a bear, then you would first feel fear, and then have goose bumps.

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So, the Cannon-Bard theory is the polar opposite of the James-Lange theory. It’s sort of like a debate of which came first, the chicken or the egg?

Here the bottom line for the Cannon-Bard theory:

Brain produces subjective feeling -> then bodily sensations follow.

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However there is evidence that contradicts this theory: forcing yourself to smile makes you happier and some drugs which reduce heart rate decrease the subjective feeling of anxiety.

Moreover, studies investigating physiological responses to ‘angry-face’ stimuli, have found autonomic responses even when participants were not aware of seeing the faces and had therefore no conscious feeling of fear.

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In case you missed it:

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Papez circuit

It seems quite clear that there is not established order in which emotional reaction and subjective feelings interact. Therefore, we need a better understanding of what actually happens in the brain. Historically, researchers have been looking for a single centre for emotions. In particular, they focused on the limbic system.

In the 1930s, Papez highlighted a circuit involved in emotions.

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Papez suggested that the neocortex, in charge of the emotional colouring, inputs to the cingulate cortex (controlling emotional experience) which in turn inputs to the hippocampus.

Then, the hippocampus inputs to the hypothalamus (in charge of emotional expression), which inputs to the anterior nuclei of the thalamus, which in turn send signals back to the cingulate cortex.

Note that all the connections are bidirectional.

MNEMONICS:
Neocortex, Cingulate Cortex, Hippocampus, Hypothalamus, Anterior nuclei of the Thalamus
Nick Chose to Have Hamburgers After Training

Nowadays there is evidence that not all the structures present in the limbic system are involved in emotion and that there isn’t a SINGLE emotion system. There are different systems underlying different emotions and the neural substrates that process emotions are not exclusively involved in emotion processing. For example, see Damasio and colleagues’ 2000 PET study

(http://www.nature.com/neuro/journal/v3/n10/full/nn1000_1049.html).

 

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The brain regions that have consistently been found to be involved in emotion processing are: Hypothalamus, Amygdala, Ventromedial Prefrontal Cortex (orbitofrontal cortex) and Insula.

To remember this, I Have A Very Pretty Cat.

Hypothalamus

The hypothalamus has been found to be important for generating emotional responses (changes in the ANS and hormonal changes).

Moreover, it has been associated with aggressive behaviour.

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Amygdala

  • The amygdala’s main job is in the experience of fear and aggression

It was first discovered in studies on the Klüver-Bucy syndrome; monkeys with temporal lobes removal showed absence of fear and aggression.

They also showed hyper-sexuality, visual recognition problems and oral tendencies.

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Overall, researchers concluded that if you remove/damage the amygdala, then you won’t be able to change emotion states.

Screen Shot 2016-06-07 at 22.31.14The amygdala responds to:

Unconditioned stimuli:

  • loud noises
  • looming and sudden movements
  • painful stimuli
  • fearful faces
  • emotionally laden stimuli

Conditioned stimuli:

  • signals
  • memories and images that were previously associated with danger (conditional learning)

How does a stimulus elicit amygdala responding?

According to Joseph LeDoux there are 2 routes involved in the process.

LeDoux

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Once the amygdala has received the indirect input from the stimulus, how does it generate the emotional response?

It has been suggested that the central nucleus of the amygdala inputs to the hypothalamus, giving rise to the emotional response, and to the periaqueductal grey matter in the brainstem, which is in charge of the behavioural reactions.

The basolateral nuclei of the amygdala, instead, input to the cerebral cortex, which is in charge of the emotional experience.

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Ventromedial prefrontal cortex (orbitofrontal cortex)

The Ventromedial prefrontal cortex is extremely important for emotional feelings, social interactions and decision making.

It was first described in the case of the patient Phineas Gage (1848), who, during an incident at work, had a rod that went through his head (ouch).

After surgery, he recovered his normal intelligence but changed in his social behaviour. The ventromedial prefrontal cortex was damaged and scientists were able to link it to the change in social behaviour.

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Iowa Gambling Task:

Nowadays we know that the Ventromedial prefrontal cortex is also involved in decision making- e.g. patients with ventromedial lesions have poor performance on tasks such as the Iowa Gambling task.

The Iowa gambling task is a essentially a game that is used in research to measure decision making ability.

Selecting decks A + B will result in high immediate gains but high overall losses. Whereas, decks C + D will result in lower immediate gains but low overall losses.

How well an individual performs during the game largely relies on the individual’s gut reactions and thus, emotion plays a crucial role during this task.

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Insula

This lil dude’s job is to create:

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The researcher, Damasio, also claimed that the insult had a part to play in changing gut reactions into subjective feelings.

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And there it is; so now, the next time you watch a puppy video and cry, you’ll know what’s happening in your brain.

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Image source: classroomclipart.com

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Think you’ve got it?

Test yourself here.

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Words: Ilaria Lisi – Blogger

Some more words: Hannah Slack – Director

Edited: Hannah Slack

Images: Ilaria Lisi and Hannah Slack

How to Study the Brain

As scientists, what methods and strategies would we use to study the central nervous system?

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The first thought that might come to mind is Brain imaging.

In cognitive neuroscience, the use of Magnetic Resonance Imaging (MRI) and functional Magnetic Resonance Imaging (fMRI) are techniques used to record and analyse brain activity.

 

MRI (structural – clues in the name!)

Yes you guessed it; MRI looks at the structure of the brain and uses a magnetic field through the whole of the brain in order to produce an image. The procedure of an MRI is broken down into steps:

1) Firstly, A radio frequency wave then passes through the brain

2) The nuclei flip and fall in line with the magnetic field, then fall back after the radio pulse

3) The images for the scan are captured when the nuclei fall back to their original position as they release the energy that is captured from the pulse.

Why we like MRI

  • Gray and white structures of the brain
  • Finds lesion that may have destroyed a part of the brain
  • Show swelling and inflammation
  • Safe, no radiation

Why we don’t like MRI

  • It’s really quite loud and patients are asked to go into an enclosed space, so it might not be suitable for children or pregnant women
  • The scan does not show bone or calcium
  • MRI requires a large amount of electrical supply

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fMRI – (functional – think inside the brain!)

In simple terms, fMRI records brain activity by detecting changes in blood oxygenation and flow that occur as a result of stimulated neural activity.

For instance, on an fMRI scan a brain area is more active when there is more oxygen and blood flow, this will be highlighted on the brain scan in response to a cognitive task.

Again this will be demonstrated in a few steps:

1) Oxygen is delivered to neurons by haemoglobin in capillary red blood cells.

2) When neuronal activity increases there is an increased demand for oxygen and the local response is an increase in blood flow to regions of increased neural activity.

3) BOLD (blood oxygen level dependent signal) is generated which I captured on the scan.

A cognitive task increases brain activity in certain region = oxygen increases and therefore blood flow increases which highlights the area on the scan.

Why we like fMRI

  • We can localise different areas of the brain that show a correlation with different mental processes
  • Non-invasive
  • Good spatial resolution and temporal resolution
  • Fast to obtain an image
  • Safe, no radiation

 

Why we don’t like fMRI

  • It can be expensive
  • May capture unwanted artefacts
  • Indirect measure

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So what is the difference between fMRI and MRI?

  • FMRI is particularly used when correlating brain and behaviour and overlapping and non-overlapping patterns of brain activation gives us insight into whether certain brain regions share distinct mental processes, as the scans show us distinct maps of the brain.

 

  • Where as MRI scans do not detect blood flow, they show dimensional pictures of the anatomical structure of the brain through the different types of tissue.

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Behavioural studies

We can also study the brain through behavioral analysis.

Behaviour analysis is used as a result of a person suffering from a brain injury and is more often used for single case studies supported by neuroimaging methods to aid their recovery.

Behavioural evidence can tell us about single and double dissociations. A single dissociation is observed in a behavioual task, where a variable leaves one cognitive function (say, A) in tact whilst clearly showing an impairment in another (say, B).

Evidence of a single dissociation clearly shows that functions A and B are partly independent of each other and do not solely rely on the same region in the brain.

A popular example of a behavioural study in the field of memory that shows single dissociation is H.M.

H.M. was shown a five-pointed star but when he was able to trace the outline of the star, he was only able to look at his reflection in the mirror to see what he was drawing.

Over the ten trials, H.M. acquired the mirror-drawing skill and even improved after the trials, yet he had no recollection of participating in any of the tasks (Squire, 2009).

Therefore from H.Ms case study we can see that H.M. has preservation in motor memory (A) because he improved and remembered how to draw the star, however because he had no recollection of participating in the task his declarative memory (B) was clearly impaired.

What can we infer from single dissociations?

These tasks use different resources but we cannot reliably conclude two functions are located differently in the brain.

A double dissociation however, can tell us that two functions are localised differently in the brain, this can be observed with two subjects that have different lesion sites.

A double dissociation will show that the first patient will do well on task A but not Task B. Whereas, the second patient will not be able to complete task A but do well on task B as shown in the table below:

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Knowlton et al (1996) research is an example of double dissociation. Amnesic subjects were compared to healthy subjects in a task that required them to predict the weather using associations that were learnt and formed gradually across the experimental trials (Knowlton et al, 1996).

It was found that patients that suffered from amnesia were severely impaired when they were tested about semantic facts about the conditions yet showed improvement in probabilistic association across the trials.

These findings were compared to a study on patients with early Huntingdon’s disease, and showed the opposite pattern of findings and were weak at probabilistic associations but had good intact memory for facts regarding the conditional training.

Thus, from double dissociations we can infer that cognitive tasks rely to some extent on different brain structures, as shown in patients that have different lesion sites.

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Positron Emission Tomography (PET) scans

 PET scans are used to examine the relationship between the metabolic activity in the brain and mental processes.

Researchers can monitor a PET scan while a person thinks about different things; therefore researchers can continuously observe areas of the brain being activated when they use subjects in their research.

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Why we like PET scans

  • Neurons whose cell bodies are located nearby will be stimulated but axons passing through the region will not be affected
  • PET scans detect active regions of the brain only

 

Why we don’t like PET scans

  • Invasive as it requires radioactive material being injected into a subject
  • Not as good spatial clarity and temporal resolution
  • High operating cost
  • They loose their radio activity very quickly as the chemicals decay

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Electrophysiology

Okay, so there has been a lot of information to take in but we are finally on to the last imaging technique used in psychology!

The last imaging technique we are going to gently touch on is methods in electrophysiology.

In electrophysiology there are two types of methods used, an MEG and an EEG.

MEG (magnetoencephalography)

This is like the EEG’s more successful brother. He probably graduated from Oxford, drives a flash car and has some big corporate job.

MEG is a direct measure of brain function unlike fMRI and PET, an MEG scan is a recorded outside of the head and produces an image by picking up the magnetic field generated by the brain.

The magnetic field passes through the skull and the brain.

Why we like MEG

  • Non-invasive – suitable for children!
  • Good for repeated measurements in healthy subjects and patients
  • High temporal resolution (milliseconds)
  • Excellent spatial resolution

 

Why we don’t like MEG

  • The equipment requires to be in a magnetically shielded environment
  • The subject needs to keep still and not move their head – not ideal for children

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EEG (electroencephalogram)

  • EEG (single unit recording) is used to diagnose epilepsy and can be used in situations where clinicians and researchers believe that a procedure of study that person’s brain can further damage it.

 

  • During an EEG electrodes, which will resemble flat metal discs, will be attached to your scalp, will take direct single unit recordings. This means that they record neural activity of single neurons when brain cells send messages to each other. After, the electrical potential of each electrode can be measured.

 

  • Also, there are EEG surface recordings are used to study areas in psychology such as sleep, but for now we will focus on the benefits and limitations of the single unit recording.

 

Why we like EEG

  • Quick to use
  • Time resolution
  • Shows the electrical activity within the entire brain

 

Why we don’t like EEG

  • Single unit recordings can be invasive
  • Limited depth

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 Think you’ve got it?

Test yourself here.

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Words and Images: Rhiannon Kilgariff – Blogger

Edited: Hannah Slack – Director

One terrible MEG joke: Hannah Slack – Director

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References

Carson, N. R. (2013). Physiology of Behaviour. Pearson.


Knowlton et al (1996). Dissociations within non declarative memory in Huntington’s disease. Neuropsychology (4) 538-548.

Squire, L (2009). The legacy of patient H.M. for neuroscience. Neuron (1)6-9.

 

The Primary Visual Pathway

Primary Visual pathway

Ever wondered how is it possible that you are able to see things? And in colour?? Well you’re in the right place to find out.

Let’s take a look at the primary visual pathway, i.e. all the bits in your eyes and brain that allow you to see stuff. Here’s a summary of it:

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Primary visual pathway runs from eyes to primary visual cortex (striate cortex, V1) in the occipital lobe.

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Retina

The retina receives information from the outside world in the form of light reflected by objects.

This information is processed firstly by Photoreceptors, who then input to Bipolar Cells which in turn input to Retinal Ganglion Cells. Let’s take a look at Photoreceptors.

Photoreceptors

There are two main kinds of photoreceptors: Rods and Cones. These differ from each other for their main characteristics and tasks.

To remember these, try and associate Rods with ‘roads and Cones with ice-cream!

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Rods

Rods are very large in number (there are loads of roads in the world!): there are circa 120 million rods in the retina of one eye.

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This type of photoreceptor is not colour sensitive, i.e. it does not discriminate between different wavelengths:

It doesn’t matter the colour of the car you drive, you can drive anywhere!

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Rods are sensitive to low light levels (can’t really drive in the dark unless you’ve got lights on, can you?) and are concentrated mainly in the retinal periphery.

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Finally, rods are able to track rapid changes (like when you’re driving over the speed limit and the cops manage to track you down. Been there).

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Cones

Cones are not as abundant as rods (circa 6 million in the retina of each eye).

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They are colour sensitive; they can, in fact, discriminate between short, medium and long wavelength, which determine the colour of the object you are seeing. When you get an ice cream, you can definitely distinguish between different flavours!

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Cones are not particularly sensitive to low light levels (you can always have an ice cream, no matter how dark it is outside).

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They are mainly concentrated in the fovea.

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Finally, cones are unable to track rapid changes (can you really run and eat an ice cream at the same time? Well, if you can, fair play to you. I can’t.)

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Rods vs Cones

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Photoreceptors and bipolar cells

Once photoreceptors have detected light, they input to bipolar cells, which can either excite or inhibit retinal ganglion cells.

When stimulated, both photoreceptors and bipolar cells vary their voltage (analogue signal), whereas all subsequent cells vary spike rate (all or-nothing, digital signal).

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Receptive fields of visual neurons

The receptive field is the part of the retina/visual field in which visual stimulation will evoke a change in the firing rate of a given visual neuron.

 

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Think about it this way: in a football game, if the ball does not go into the goal, you will not get a standing ovation from the audience.

If the audience is our ‘given visual neuron’, then the goal is its receptive field. A stimulus (i.e. the ball) will only evoke a change in the firing rate (standing ovation) of the neuron if it is in the receptive field (goal).

footballer
Image source: classroomclipart.com

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You could also remember it like this:

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Imagine the visual neurons are security cameras operating in an art gallery.

The visual field would be the main room of the art gallery and the receptive field would be the area of that room that the security cameras can see.

As soon as a burglar (stimulus) enters the area that the security camera can see (the receptive field), the security cameras set off the security alarm (the neuron reacts and changes it’s firing rate).

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Picky neurons

However, these neurons are picky devils. Sometimes, they won’t change their firing rate unless a stimulus is presented in a certain way within their receptive field. This is called the “substructure” of that receptive field.

left-visual-field-3left-visual-field-4

For example, a neuron might have a substructure that means they’ll only fire if a stimulus is presented the right way up in their receptive field.

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Retinal ganglion neurons

As we said, RGCs, receive input from bipolar cells.
RGCs have ON-OFF centre surround receptive fields. And no, I didn’t just write down some random nouns, it actually means something; let’s break it down.

Each receptive field is composed by a central disk, the “center”, and a concentric ring, the “surround”, with each region responding oppositely to light.

For example, light in the centre will increase the firing of a particular RGC, whereas light in the surround will decrease its firing.

Now, the light presented in ‘ON’ regions excites the cell, whereas the light in ‘OFF’ regions inhibits cell.

The overall response rate of a single cell is based on the sum of stimulation in ON region minus stimulation in OFF region.
The following picture is going to be an extremely accurate representation of what happens when light is presented in the ON and OFF regions of a receptive field of a RGC. Not really.

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The centre-surround light opponency is particularly important for objects’ edge detection, regardless of light levels in the environment.

And one more time:

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Lateral Geniculate Nucleus (LGN)

Neurons in the lateral geniculate body respond to visual stimuli in similar ways to retinal ganglion cells, i.e. their receptive fields are organized in an ON-OFF centre surround fashion.
Both the LGN and the RGCs are colour sensitive, and the neuron’s receptive fields show centre surround colour opponency.

colour opponency.png

The functional significance of colour-opponency is not clear yet.

However, colour opponency can explain negative afterimages: the human visual system processes colour information from signals gained from the cones and rods in an antagonistic manner.

There are three opponent channels: red-green, blue-yellow, and black-white. Responses to one colour of an opponent channel are antagonistic to those to the other colour. It follows that a green image will produce a red afterimage.

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The primary visual cortex (Striate cortex, V1)

The primary visual cortex (comprising striate cortex and the area V1) is located in the occipital lobe.

brain.png
Image source: wikipedia

Most V1 neurons are orientation sensitive, i.e. they respond best to elongated stimuli with specific orientations.

There are two main types of orientation-sensitive V1 neurons: simple cells, and complex cells.

  • Simple cells

Their receptive fields have inhibitory and excitatory regions and can be thought of as combining inputs from ON and OFF cells.

Simple cells respond best to appropriately oriented stimuli placed in a certain position within the receptive field.

 

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  • Complex cells

Their receptive fields have no discrete ON and OFF region and can be thought of as combining inputs from simple cells.

Complex cells respond optimally to appropriately oriented stimuli placed anywhere within the receptive field and to moving stimuli (reflecting response adaptation).

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When trying to map the Primary Visual Cortex, different criteria can be adopted.

If we map the visual inputs from the retina to the cortex, we obtain a retinotopic map.

If we map the cortex on the base of the characteristics of stimuli to which neurons respond best to, we obtain columnar modules; for example, all the neurons responding to vertical stimuli will be ‘stacked’ in the same column, which will be different from the one where neurons responding to horizontal stimuli will be ‘stacked’.

After the information is passed from the retina to the primary visual cortex, it will be analysed in more detail in the visual association cortices (V2-V5, inferior temporal cortex and parietal cortex) in order to form the ‘holistic’ (i.e. integer, complete) representation of objects and visual scenes, and store it into memory.

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In case you missed it:

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Think you’ve got it?

Test yourself here.

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Words: Ilaria Lisi – Blogger 

Edited: Hannah Slack – Director

Images: Ilaria Lisi and Hannah Slack

Update

Quick update,

Apologies for the lack of posts this week but I am currently training a new team of bloggers to work with me on the blog! (Exciting!).

Also, there will no longer be a fixed post time. This is simply because this will better fit around my studies. However, fear not, content will be fully available ready for peak revision time (ie April)!

Also the blog posts may not necessarily follow the lecture sequence on the C81BIO module. I have surveyed last year’s first years and have determined which lectures people find most difficult. These lectures  that were scored as most troublesome will be made priority over others to ensure that the blog is as effective as it can be!

Be sure to like the Facebook page and follow the blog on social media so that you never miss a post!

Best of luck with your studies everyone!

Hannah

Owner/Director – Psychology and Neuroscience 101

Transmission between neurons

Transmission between neurons

In this post, we will look at how two neurons send a message between each other.

Just like two people can be said to share a chemical attraction, the process of two neurons sharing information is also a chemical affair.

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Synapse

The synapse occurs at the point where the terminal button of one neuron meets the membrane (dendrite or soma) of another neuron.

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The is a small gap between the synapse and the membrane known as the synaptic cleft. Information travels through A’s synapse, across the synaptic cleft and into the receptors on neuron B.

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Synaptic transmission

Synaptic transmission basically refers to the delivery of a message via a synapse.

Synaptic transmission is a chemical process (as mentioned above) that deals with neurotransmitters.

Here is the process of what happens during synaptic transmission:

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Binding

Let’s take a closer look at exactly what happens at step 7, when the neurotransmitter binds to the post-synaptic cell. (The post-synaptic cell is basically the one that’s doing the receiving).

The receptors in the membrane of the post-synaptic cell contain these things called ion channels. You can picture these as doors into/out of the cell.

These ion channels either let ions in or out of the postsynaptic cell.

The method in which these ion channel doors are opened involves things called neurotransmitters. The role of a neurotransmitter is to bind themselves to a receptor’s binding site. This will let the receptor’s ion channel will open and allow ions to move either in or out of the postsynaptic cell.

So, think of the neurotransmitters as being little keys and the binding sites on the receptors are the locks. Binding to a binding site unlocks the door and opens the ion channel door.

However – there’s a catch, each neurotransmitter will only bind to one certain type of receptor. For instance, one neurotransmitter may only bind to a binding site on a receptor that handles Na+ ions (i.e. one with an ion channel that lets Na+ ions into the cell). Another may only bind to a binding site on a receptor that handles K+ ions, etc.

This is called a lock and key system. Each neurotransmitter only binds to one type of receptor, in the same way that one key can only unlock one lock.

Remember – letting ions into and out of the cell creates a certain postsynaptic potential (fancy name for the receiving cell’s charge).

The postsynaptic potential that is created (excitatory or inhibitory) depends on which ion channel (door) is unlocked and thus, which ions are moving into/out of the cell.

You can have two types of postsynaptic potential:

  • EPSP = excitatory postsynaptic potential
  • IPSP = inhibitory postsynaptic potential

An EPSP basically means that the receiving neuron cell has been encouraged to fire and send on the message to other neurons.

So, if your neurons were passing along this message: “JUMP”, a specific ion channel would be opened on the postsynaptic cell that would allow a certain type of ion through that would result in the creation of an EPSP.

This would encourage the neuron to fire and pass on the message to other neurons, leading to the behaviour eventually being carried out.

Whereas, an IPSP means that a receiving neuron has been discouraged from firing and sending on the message.

So, if the message were “DON’T OPEN YOUR HAND AND DROP THE BOILING PAN OF WATER”, then a different ion channel would open on the postsynaptic cell that would allow a different type of ion to enter/leave the cell, thus creating an IPSP.

This would prevent the neuron from firing and thus, stop you from opening your hand and dropping the pan.

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But which ions create an EPSP and which create an IPSP?

I’m glad you asked.

 

Na+

Na+ can only move INTO the postsynaptic cell and not out. If a whole lot of Na+ does enter the postsynaptic cell then an EPSP is created. This means that the cell will become depolarised (when the postsynaptic cell’s charge moves closer to zero).

Try imagining that the postsynaptic cell is in financial debt and the Na+ ions are a form of currency. As more Na+ ions enter the cell, the cell’s outlook on life becomes less negative.

Postsynaptic cell-4.jpg

Also, you can remember that depolarised = moves closer to zero because polarised = gains electric charge so depolarised must mean that it is losing that charge.

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K+

K+ can only move OUT of the postsynaptic cell. If a lot of K+ does exit the cell, then an IPSP is caused in the postsynaptic cell. This hyperpolarises the postsynaptic cell, making it more negative.

Imagine that the post-synaptic cell is upset that all the K+ ions are leaving, like it’s losing it’s babies, so as a result it has a more negative outlook on life.

Postsynaptic cell-3.jpg

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Cl-

Cl- can only move INTO the postsynaptic cell. If lots of Cl- enters the postsynaptic cell, then an IPSP is caused in the postsynaptic cell. This hyperpolarises the postsynaptic cell, so that it becomes more negative.

Imagine that the  postsynaptic cell is enjoying it’s life, minding it’s own business, then a hoard of Cl- ions move into it’s membrane – disturbing it’s peace. This leaves the postsynaptic cell feeling rather negative. Like when your younger siblings burst into your room and ruin your peaceful chill time.

Postsynaptic cell.jpg

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Ca2+

This one is a sneaky one. He’s very different from the rest. Be sure to look out for him. Basically, Ca2+ can only move INTO the cell and once it is in there it’s main job is to activate enzymes. Forget all that IPSP and EPSP nonsense, Ca2+ ain’t go time for that.

Postsynaptic cell-5.jpg

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In summary:

Na+.png

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Confused?

Let’s go through it again from the top:

(NT = neurotransmitter)

KeyMessage board

Message board-3

Message board-4

 

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Message board-5Message board-6Message board-7

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So, as you can see, the neurotransmitters work as keys to unlock the ion channel doors on the receptors, so that ions can pass in and out of the cell. As ions pass in and out of the cell, the appropriate PSP (postsynaptic potential) is created that either encourages or discourages a given behaviour from happening.

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Receptors

Receptors sit on the edge of the post-synaptic cell and their job is to receive the incoming ions/messages.

Receptors come in two types:

  • ionotropic receptors
  • metabotropic receptors

Both types have binding sites. Binding sites are the points where the neurotransmitter attaches to the receptor, thus opening the ion channel and allowing ions to enter the post-synaptic cell.

Ionotropic receptor (eye on oh trow pik) – Direct method

psychologyandneuroscience101.wordpress.com-33.png

With an ionotropic receptor, the ion channel on the receptor will only open when a neurotransmitter binds to that receptor’s binding site.

Think of the neurotransmitter as a key to open the receptor’s “ion channel” door. The binding site would then be the lock.

This method is good for things that you need to be updated quickly – like your sense of sight and hearing.

Think DIRECT = QUICK.

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Metabotropic receptor (meh tab oh trow pik) – Indirect method

NT-2.png

The use of metabotropic receptors makes up the indirect method of transmission between neurons.

This is how metabotropic receptors work:

NT binds to the ion channel.png

Here’s a plain text version too (for access reasons):

  1. NT binds to the ion channel (NT= neurotransmitter)
  2. This activates the G-protein
  3. G-protein activates an enzyme
  4. Enzyme produces second messengers (blue arrows on diagram)
  5. Second messengers open the ion channels

So, as you can see, they work using a chain reaction.

This chain reaction means that postsynaptic potentials (PSPs) are produced slower than those made by ionotropic receptors.

This is good for stuff that you need to last for a while, for instance, sense of taste, smell and pain.

You can try and remember that metabotropic receptors form the indirect method of transmission between neurons by associating “metabotropic” with the term “meta”.

When a piece of creative work is termed as meta, it usually means that it indirectly refers to itself or it’s genre/industry. An example of a meta-movie could be a movie about people making their own movie about the film industry. Therefore, the meta-movie would be an indirect comment on itself/it’s industry.

Thus, we can think metabotropic = meta = indirect method.

Likewise, we can then remember that ionotropic receptors must be the direct method by default.

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Image credit: memegenerator.net

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Termination

Let’s look more closely at how the excess neurotransmitter left outside the cell dissipated away.

This dissipation mainly happens via two ways:

1. Enzymatic deactivation/degradation 

Cerebrum-4.jpg

The neurotransmitter is eventually broken down by an enzyme into other substances.

e.g., acetylcholinesterase (a see tul koh lin ess ter ace) breaks down Ach into choline and acetic acid.

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2. Reuptake

Cerebrum-3.jpg

The excess neurotransmitter is taken back into the presynaptic terminal (the cell it just came out of).

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Neural integration

Cerebrum-5.jpg

The excitatory PSPs (postsynaptic potentials) increase the chance that the neuron will fire.

Whereas, the inhibitory PSPs decrease the chance that the neuron will fire.

Integration is basically the fancy term for when you take the excitatory PSPs then take away the inhibitory PSPs.The total postsynaptic potential from that equation determines whether the neuron will actually fire or not.

(Note: the numbers in the picture above are meaningless and are merely to illustrate the integration process)

Important points:

It is important to remember that inhibitory PSPs don’t always inhibit behaviour.

If there’s an inhibition of inhibitory neurons then there’s a greater chance of behaviour occurring .

E.g. So, an inhibitory neuron may be stopping you dropping a heavy bowling ball that you’re carrying onto your friend’s foot. Use an IPSP to inhibit those neurons (turn them off) and you’ll have one less friend…and your friend will have one broken foot.

If there’s an excitation of inhibitory neurons then there’s less chance of behaviour occurring.

E.g. So, another inhibitory neuron might be stopping you from dropping a pan of boiling water onto your foot. Luckily for you, using an EPSP to excite this neuron boosts its inhibiting power meaning that you are extremely unlikely to drop the pan.

Think of EPSPs and IPSPs like potions or pills. If an inhibitory neuron takes an EPSP pill, it becomes excited and does it’s job of inhibiting behaviour twice as hard. If an inhibitory neuron takes an IPSP pill, it becomes inhibited and is less effective at it’s job of inhibiting behaviour.

(Side note: don’t do drugs, kids)

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Neurotransmitters

The following neurotransmitters are all actually amino acids.

Let’s look at some of the main neurotransmitters and what they do:

Glutamate

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Glutamate is the most common excitatory neurotransmitter floating around in your CNS (central nervous system).

It’s unique in that it has the ability to bind to a large number of receptors.

Glutamate is particularly important for learning and memory processes.

You can remember this because you can say that glutamate makes information stick in your head like glue.

Screen Shot 2016-06-07 at 22.27.56GABA (gamma-aminobutyric acid)

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GABA is the most common inhibitory neurotransmitter in your CNS.

This means that GABA’s main job is to lower the likelihood of a neuron firing.

Basically, GABA is a massive party-pooper.

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Acetylcholine (ACh) (a see tul koh leen)

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Image credit: muscle image from Clker.com

ACh is a neurotransmitter that is located in both the CNS and the PNS (peripheral nervous system).

In particular, ACh is usually located at neuromuscular junctions.

Hence, ACh has a big role in muscle contraction.

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Some poisons have been created that exploit the use of ACh in the CNS:

  • Curare (kew rahr ee)
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Image credit: muscle image from Clker.com

Curare is an ACh antagonist. This means that it blocks the functioning of ACh.

By doing this, curare effectively prevents muscle contraction from happening, leaving the victim paralysed.

  • Muscarine
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Image credit: mask from Clker.com

Muscarine is an ACh agonist. This means that is disguises itself as ACh, thus creating a battle between itself and the genuine ACh at binding sites.

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Uses for these poisons

These two poisons have actually been put to use in:

  • hunting (by using darts coated in curare to paralyse a target)
  • surgery (as a local anaesthetic)

Hunting.jpg

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Monoamines

The following neurotransmitters are known as the monoamines.

They are made by the neurons in your brain.

They are also G-protein coupled (so, they have a G-protein attached to them. Don’t worry too much about this – just remember it).

The monoamines can be either excitatory or inhibitory – it all depends on which receptor subtype they bind to. In a sense, they’re kind of like chameleons.

Let’s take a look at two member of the monoamine family and what jobs they do:

Dopamine:

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Think of dopamine as a drug baron (stay with me here).

The things it cares about are:

  • motor control (being in control of your body)
  • reward (such as cold, hard cash)
  • addiction (dopamine explains why many drugs are so addictive)

Looking at it like that, it would be easy to picture a dopamine as a greedy, cruel drug baron. We could even call him Donny “the drug lord” Dopamine.

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Image credit: Clker.com

Serotonin:

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Serotonin is another member of the monoamine family.

Serotonin is basically a stereotypical mum. It has many jobs to do in order to keep you functioning, these include:

  • Checking that you’re feeling okay (mood regulation)
  • Making sure you’re eating right (regulating eating)
  • Making sure you’re getting enough sleep (regulating sleep)
  • Making sure you’re paying attention when crossing the street etc (regulating arousal)
  • Letting you know when to stop doing something before you get really badly hurt (experience of pain)
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Image credit: Clker.com

Screen Shot 2016-06-07 at 22.31.14Think you’ve got it?

Test yourself here

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Transmission within a neuron

Transmission within a neuron

This post will focus on the transmission of information within a single neuron, i.e. how information moves through a single neuron.

Transmission within a neuron is an electrical process (which is the focus of this post).

Transmission between two different neurons is a chemical process (the focus on the next post).

How to remember this is seen here:

This is JeffThis is Jeff-2This is Jeff-3This is Jeff-4

So, the attraction between Geoff and Suzie is chemical. Much like how the transmission between two different neurons is also chemical (chemical process).

The surge that Geoff felt within his own heart was electric. Much like how the transmission within a single neuron is also electric (electrical process).

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Every cell in your body will carry an electrical charge

However, whether this charge is positive or negative differs between the inside and the outside of the cell.

All cells can be thought of as Regina George from the movie “Mean Girls”. If you haven’t seen Mean Girls then think of a person who smiles at your face but secretly hates you.

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Like Regina George, cells are positive on the outside but negative on the inside.

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Resting potential

First, let’s look at what actually makes up a cell:

 

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The membrane carries an electrical charge known as the membrane potential.

The membrane potential is essentially the difference between the electrical potential inside the cell and the electrical potential outside the cell:

Membrane.png

 

 

 

 

 

 

 

 

 

 

The membrane potential of the cell when at rest (when everyone just chilling and no info is being transmitted) can also be called the resting potential.

For a neuron, the resting potential is -70Mv.

Neurons send information to other neurons by temporarily altering the their overall polarity (electrical charge).

Membrane potential is altered by the movement of ions in and out of the cell.

The ions are prevented from moving in and out of the cell by these two forces:

  • Diffusion
  • Electrostatic pressure

Here’s a reminder of what those two forces actually are, in case all that GCSE knowledge has escaped you:

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Diffusion: molecules (water in the example) move from an area of high concentration to an area of low concentration.

Electrostatic pressure

Electrostatic pressure: the electric charge of each molecule determines whether two molecules will attract or repel each other.

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Ions

What are ions anyway?

The cell contains many charged molecules called ions.

Ions come in two flavours:

  • Cation (+vely charged ions)
  • Anion (-vely charged ions)

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The fluid inside the cell is called the intercellular fluid. This contains potassium (K+) ions.

The fluid outside the cell is called the extracellular fluid. This contains sodium (Na+) and chloride (Cl-) ions.

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The ions at resting potential

“What’s this about K+, Cl- and Na+?”, I hear you ask.

To understand more about these ions and what role they play in the transmission of information within a single neuron, let’s look at how they behave at resting potential.

At resting potential, no information is being sent down the neuron, so the ions do not move. You can think of this as their default state.

To understand how they all behave at rest, we are going to imagine that this cell is actually a nightclub, because what else do ions when they aren’t working but go clubbing?

K+ (inside)

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Diffusion: means that, although the K+ ions aren’t moving yet, they WANT to move out of the cell, which has a lower concentration of K+ ions than the inside of the cell.

BUT

Electrostatic pressure: means that the K+ ions are attracted to negative inside of the cell.

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Cl- (outside)

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Diffusion: means that the Cl- ions want to move in to the cell, which has a lower concentration of Cl- ions than the outside of the cell.

BUT

Electrostatic: means they are repelled by the negative inside of the cell.

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Na+ (outside)

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Diffusion: means that the Na+ ions want to move in to the cell, which has a lower concentration of molecules than the outside of the cell.

AND

Electrostatic: means that they are attracted to the negative inside of the cell.

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So, all in all:

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Sodium-potassium pumps

Okay, so eventually, a lot of Na+ ions travel into the cell and quite a few lucky K+ ions manage to sneak out as the concentration inside the cell increases.

Now, what happens next?

Well, that’s where the sodium-potassium pumps come in. Their purpose is to pump all the Na+ ions out of the cell and pump the escaped K+ back into the cell.

To remember this, let’s go back to the nightclub analogy:

psychologyandneuroscience101.wordpress.com-21.png

So, that’s how the ions behave at rest. However, when a piece of information needs to be sent down a neuron, the neuron undergoes a rapid change in electrical charge. This new charge is called the action potential.

It’s like on weekends when it’s just chilling, the neuron has a resting potential. But when it need to work and send signals, it has an action potential.

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Action potential

An action potential is a rapid change in the polarisation (electrical charge) of the neuron in order to send a signal down said neuron.

For this signal to be sent, the neuron must first gain enough action potential to reach the threshold of excitation.

THE THRESHOLD OF EXCITATION.pngThink of the threshold of excitation as a big red button. The neuron must have reached a certain action potential in order to push this big red button.

Pushing the big red button, i.e. reaching the threshold of excitation, then causes the neuron to fire it’s signal down the axon by allowing the ions to finally move in and out of the cell.

This is an “all or nothing” process, the neuron either fires or it doesn’t.

During the process of the neuron firing, voltage-dependent ion channels open or close depending on the current membrane potential of the neuron (hence, voltage-dependent). These ion channels are what allow the ions to enter/leave the neuron, they’re like little doors really.

At various parts of the firing process, the neuron is depolarised and hyperpolarised:

  • Depolarisation: decrease from normal resting potential (overall charge moves closer to zero) – if polarisation means electrical charge then de-polarisation means less charged.
  • Hyperpolarisation: increase in action potential (the overall charge becomes more negative).

 

Here’s the process of the neuron firing:

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Now let’s look at the process in more detail:
Na+ channels open.Na+ channels open.-2psychologyandneuroscience101.wordpress.com-13

The point of becoming a refractory is to stop the neuron from firing a second time since it is still over the threshold of excitation (see above graph).

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Saltatory conduction

Jump

 

The gaps in myelin sheath are called the nodes of Ranvier.

As the action potential travels down the axon, it is regenerated at these gaps. This makes it look like the action potential is jumping down the axon.

This process is called saltatory conduction because the word saltare means to “to jump“.

But why?

This process allows for:

  • Fast conduction – travels down axon faster.
  • More energy efficient

Under the myelin sheath, decremental conduction occurs. This is when the action potential decreases as it moves down the axon. However, the action potential is then regenerated to its full strength at each node of Ranvier. Therefore, saltatory conduction is energy efficient.

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So, it looks like the full strength/size action potential is jumping down the axon:Jump-3

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Think you’ve got it?

Test yourself here.

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What is a neuron?

The neuron

First things first, let’s start with what a neuron actually is.

GCSE Biology coming at you in 3…2…1…

Dendrites.png
Image source: edited from pixabay.com

Soma – this is the part of the cell that contains the nucleus

Dendrites – these receive messages from other neurons

Axon – carries the message from the soma to the terminal buttons

Terminal buttonssends the message on to the next neuron. These sent info to another neuron’s dendrites or soma.

Myelin sheath – protects the axon / helps send the message down the axon (more on that later).

You can remember that dendrites RECEIVE messages and terminal buttons SEND messages by thinking of it like this:

Dendrites look like the roots of a tree. A tree’s roots suck up all the water and nutrients from the soil. Therefore, the dendrites suck up all the information from the other neuron.

Whereas, the terminal buttons look a bit like the end of a creepy alien finger. So, you could imagine the process of sending a message from one neuron to another as a creepy game of tag, with the terminal buttons as the fingers that are about to tag another neuron.

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Different types of neuron

main-qimg-b1ceb800ce84d9b1af847d983c66ef65.png

Neurons actually come in 3 flavours:

The one you’re probably most familiar with is called the multipolar neuron.

Multipolar neurons are identifiable by the fact that they have:

  • one axon
  • many dendrites

This is easy to remember because multi- means multiple and this neuron has multiple dendrites.

Next we have the bipolar neuron.

A bipolar neuron has:

  • one axon
  • one dendrite tree

To remember this just imagine that the multipolar neurons are pansexual and like multiple genders (or rather they have multiple ends – because multiple dendric trees).

Whereas, a bipolar neuron can be thought of like a bisexual – they like 2 genders only (or rather they have 2 ends – one being a dendric tree, one being not)

Bipolar neurons are usually located in the visual/auditory systems (sensory systems).

The final neuron is a unipolar neuron.

A unipolar neuron has:

  • one axon – divided by two branches
  • one branch receives sensory information
  • the other branch sends information to the CNS

You can think of these as heterosexual neurons. They don’t “swing both ways” (sorry) in the sense that all the information goes straight (sorry) through them. One branch receives info and the other branch sends it on to the CNS.

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Connections

biology-1295127_1280.png
image source: pixabay.com

Remember that the terminal buttons are like alien fingers that send the information. Like when, after rubbing your feet on the ground, you touch someone to give them an electrostatic shock.

Also, remember that the dendrites are like tree roots that suck up the information from the terminal buttons.

Terminal buttons can also attach on to the soma, which can also receive information in the same way that the dendrites can.

Dendrites _ Soma - RECIEVE-2

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Afferent and efferent neurons

The term “structure”refers to any part of the brain, e.g. the thalamus.

An afferent neuron is one that carries information to the structure.

Whereas, an efferent neuron is one that carries information away from the structure.

Dendrites _ Soma - RECIEVE-3

So, with an Afferent neuron – info Arrives at the structure.

And with an Efferent neuron – info Exits the structure.

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Supporting cells

A great supporting cast is essential is you’re an actor…or a neuron.

This supporting cast goes by the collective name of the Glia (“glee ah”).

The glial cells include:

  • astrocytes
  • oligodendrocytes (“oh li go den droh sites”)
  • microglia

General function:

  • support the neurons
  • take away waste
  • give nutrients to the neurons

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Astrocytes

Astrocytes are star-shaped. You can remember that because words beginning with astro- usually relate to space/stars (e.g. astronaut, astrology, astrophysics).

Astrocytes have two jobs:

  1. removal of waste
  2. synchronising neurons

Think of it like this:

Every astrocyte works two jobs. By day, Mr. Astrocyte is everybody’s favourite neighbourhood bin/garbage-ban.

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But in the evenings, Mr. Astrocyte coaches a team of synchronised swimmers and gets very competitive.

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Oligodendrocytes

Oligodendrocytes have the important job of creating the myelin sheath, which will protect and insulate the neuron’s axon. Not all of the axon is covered by the myelin sheath, but we’ll look at that in more detail when we look at transmission within neurons.

Think of oligodendrocytes as little factory workers, working hard at the myelin sheath factory.

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Microglia

These are tiny cells (duh- “micro” = small).

They function as part of the immune system.

Their main role is to remove:

  • waste
  • viruses
  • fungi

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Think you’ve got it?

Test yourself here

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Brain divisions

Do I continue writing this blog post or do I binge-watch the new season of Orange is the New Black on Netflix?

Our minds can often feel divided on a lot of things. However, we can actually divide some structures of the brain into certain groups and subgroups.

The 3 biggest divisions of the brain are:

  1. Forebrain
  2. Midbrain
  3. Hindbrain

Also known as the prosencephalon, the mesencephalon and the rhombencephalon.

The term “encephalon” (“en seff uh lon”) is just another word for the brain. It literally means “in the head”. If you learn the term encephalon then you’ll see that most other terms here are made up of encephalon + a different prefix (e.g. pros-, mes-, rhomb-).

Major divisions of the brain can also have subdivisions:

  • The forebrain (prosencephalon) has two subdivisions, telencephalon and diencephalon.
  • The midbrain (mesencephalon) has no subdivisions.
  • The hindbrain (rhombencephalon) has two subdivisions, metencephalon and myelencephalon.

These subdivisions then each contain certain structures. A summary of each division, their subdivisions and the structures within each subdivision can be seen in this table:

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Forebrain: Telencephalon’s structures

Let’s take a look at the structures within the first subdivision of the forebrain, the telencephalon. These include:

  • cerebral cortex
  • basal ganglia
  • limbic system

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The Cerebral Cortex (“sa ree brul”)

This is the outer layer of the cerebrum. You can remember this because the word “cortex” actually means bark, like the bark that forms the outer layer of a tree. The folds in the cerebral cortex exist so that the cerebrum can have a bigger surface area. A bigger surface area allows for a greater number of neurons.

The grooves in the cerebral cortex are called sulci (“sul sigh“). (Or sulcus if there’s only one). Big grooves are called fissures. Sulci begins with the letter S, as does the word “sinks” so when trying to remember what sulci are, think of it as the places where the brain “sinks” in – otherwise known as the grooves! The Sulci is where the brain Sinks in!

Another way to remember it is to imagine how you feel when you’re feeling sad. You’ll usually feel like your heart has sunk in your chest. Likewise, you may start to sulk. So, you can think of a groove as a point where the cerebral cortex has sunk like a your sad heart when you’re having a sulk-us.

The bulges are called gyri (“Jye ree“). (Or gyrus if there’s only one). When something gyrates, it swings around in a circle. For example, when you use a hula hoop, your hips gyrate as they move in a circular motion. the circular pattern that your hips trace in the air is similar to the dome-like structure of a gyrus.

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Image: adapted from classroom clipart.com
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Image: adapted from at wikipedia.com (author: Albert Kok), License: Public domain.

 

 

 

 

 

 

 

So remember, a sulcus is where the brain sinks in and a gyrus sticks out like your hips do when they gyrate.

The major sulci and gyri of the cerebral cortex are the:

  • central sulcus
  • lateral fissure/Sylvian fissure
  • precentral gyrus
  • postcentral gyrus

These can be seen on the pictures below:

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Image: adapted from clker.com
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Image: adapted from clker.com

The precentral gyrus is the bulge that comes BEFORE the central sulcus – that’s why it’s the PRE-central gyrus.

The postcentral gyrus comes AFTER the central sulcus – that’s why it’s the POST-central gyrus.

The central sulcus in the middle of the precentral gyrus and postcentral gyrus – that’s why it’s the the CENTRAL sulcus, because it’s in the CENTRE.

The lateral fissure is called a fissure because it is a GIANT SULCUS (see above). The lateral fissure carries the name “lateral” because it’s on the side of the brain and lateral just means on the side.

The lateral fissure can also be referred to as the Sylvian fissure. For the purpose of remembering this, you can imagine that it carries the name “Sylvian” simply because it wanted to be different. Think of the way that the Sylvian fissure sits away from the precentral gyrus, postcentral gyrus and central sulcus. This is a fissure that wants to stand out from the crowd and this fissure’s swanky name does just that.  However, those who really know this fissure know it by its real, not-so-swaggy name, “the lateral fissure”. Just as everyone knows a girl who refers to herself as “Juniper” on Instagram but actually has”Susan” written on her birth certificate.

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The Lobes of the Cerebral Cortex

The cerebral cortex can be divided into four lobes. These are as follows:

  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe

You can remember the names for this using the mnemonic:

Freud Tore his Pants Off.

(I recommend you check out the blog post on brain directions before reading this next part).

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Image: adapted from clker.com

So using what we know of brain directions, we can use that terminology to say how the different lobes relate to each other in location:

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For example, the frontal lobe is dorsal to the temporal lobe and rostral to the parietal lobe.

You can use something called the fist mnemonic to help you remember where all the lobes sit in the brain.

  1. First, form a fist with your hand.
  2. Then we’ll say that yourthumb/thumb knuckle represents the temporal lobe.
  3. Next, we’ll say that from the knuckles at the bottom of your fingers down to the front of your fist will form the frontal lobe.
  4. Then from those finger knuckles down to about half way down the back of your hand represents the parietal lobe.
  5. Then from half way down the back of your hand to the start of your wrist forms the occipital lobe.

 

We can also now use what we’ve learnt about sulci and gyri to know that the lateral fissure/ sylvian fissure divides the frontal lobe from the temporal lobe. Also, the central sulcus divides the frontal and parietal lobes.

 

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Major lobe functions

Okay, now let’s take a quick look the major functions of each lobe within the cerebral cortex:

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Extra information on the frontal lobe

Since the frontal lobe thinks it’s the captain of the show, naturally it would want us to talk about the individual components that make it up.
So, making up the frontal lobe, we have the:

  • Prefrontal cortex
  • Premotor cortex

So, the prefrontal cortex’s jobs include:

  • Strategy
  • Making judgements
  • Planning

The prefrontal cortex is true captain here. For example, Apple, as a company, may make decisions on what new product it creates. However, it’s the Chief Executive within the company will actually make the decision on what goes into the final product.

In this instance, the frontal lobe (company) makes the decisions. However, it is the prefrontal cortex (Chief Exec.) that makes the decisions and produces strategies and does all the planning.

The premotor cortex has the job of being in charge of something called the primary motor cortex, which you can read all about down below.

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Primary areas of the cerebral cortex

There are 4 primary areas of the cerebral cortex:

  1. primary somatosensory cortex  (touch)
  2. primary visual cortex
  3. primary auditory cortex
  4. primary motor cortex

The…

  • primary somatosensory cortex
  • primary visual cortex
  • primary auditory cortex

…receive information from the SENSES.

The…

  • primary motor cortex

SENDS information to the MUSCLES in your body.

Kind of like how a motor in a car makes the car move, your primary motor cortex tells your muscles to get moving.

Also, all the senses and motor signals are contralateral (e.g. the right eye’s connected to the…left hemisphere, the left eye’s connected to the…right hemisphere). The only exception to this is the sense of taste and the sense of olfaction (fancy word for smell).

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The sensory association areas of the cerebral cortex

48_27humancerebralcortex
There are 3 sensory association areas:

  1. Somatosensory association cortex
  2. Auditory association cortex
  3. Visual association cortex

The primary areas of the cerebral cortex (discussed above) send information to these 3 sensory association areas of the cerebral cortex for them to analyse.

So, it goes a little something like this…

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For reference,

  • The somatosensory association cortex is located in the parietal lobe.
  • The auditory association cortex is found in the temporal lobe.
  • The visual association cortex covers both the temporal lobe AND the occipital lobe (because it’s greedy).

You can remember that the visual association area covers move than one lobe by remembering that when someone is being greedy and begging for lots and lots of food, they are said to have “eyes bigger than their belly”. Now if you extend this and remember a greedy person with huge eyes, you should remember that the visual association cortex is a greedy so-and-so that gobbles up not one but two lobes of the cerebral cortex.

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Okay, I don’t know about you but I am SICK of hearing about the cerebral cortex. Let’s move on to something else.

The Basal Ganglia

The basal ganglia is essentially just a gang(-lia) of cell bodies (nuclei) living it up in your telencephalon.

The hoodlums that make up this gang-lia include:

  • caudate nucleus
  • putamen
  • globus pallidus

Now, the caudate nucleus and the putamen really come as a pair. Collectively they are known as the striatum.

The globus pallidus is like the boss of this gang-lia, with the striatum duo as his two lackeys. This is because the striatum receives all of the information (like lackeys working on a job for their boss) then sends this to the globus pallidus.

Diem-4.png
Image: stickmen images from canva.com

The functions of the basal ganglia include:

  • being in charge of movement control (intentional movement – NOT reactions)
  • being in charge of reward systems
  • motor learning

Although we said the frontal lobe of the cerebral cortex makes decisions on where we move to, etc – that is true – but what really happens is that the frontal lobe tells the basal ganglia (+ other parts of brain) where it reckons we should go and the basal ganglia then works (with other brain parts) to ensure that that movement is carried out effectively.

Motor learning is basically when your brain learns how to perform a series of actions so well that you don’t even need to think about what you’re doing to perform those actions anymore. An example would be when you enter your password on your phone. After a while your brain will have remembered the pattern that your thumb needs to move in without you even having to think about it. Another example would be when you drive a car. After a while of driving, your brain will learn in what order it needs to press the pedals and move the gear stick in order to get the car moving without it even crossing your mind.

If you want a way to remember the basal ganglia’s jobs, imagine it as a gang that mirrors a drug gang. They control the intentional movement of certain cargo (drugs) and being part of their gang could give certain financial rewards. Also, you can imagine that members of a drug can must be good getaway drivers anyone looking to join the gang must learn how to drive a motor fairly fast.

 

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Image: adapted from cliparthut.com

(Side note: please don’t set up your own drug gang…even if a job as a drug lord may pay better than whatever shelf-stacking job we all manage to find at Tesco after we leave university. R.I.P.)

If you have a lesion (big cut) in your basal ganglia, it can lead to the following disorders:

  • Parkinson’s disease
  • Huntington’s disease

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Okay, and finally we move on to the last component of the telencephalon, the limbic system.

The Limbic System

Blausen_0614_LimbicSystem.png

This is made up of the:

  • limbic cortex
  • amygdala
  • hippocampus
  • fornix
  • mammillary bodies

The general job of the limbic system includes: learning + memory 

The Amygdala

The amygdala’s unique job is to help us learn what to fear by encoding certain stimuli as scary.

You could imagine Fear from the movie “Inside Out” and the way that he senses that something Riley has encountered is scary and then reminds her that this thing is scary when she encounters it again.

You could imagine that Inside Out’s Fear has a sister called Amy G. Dala who acts exactly as he does.

The Limbic Cortex

The limbic cortex looks a little bit like a sting ray when looked at from below, so it may help to remember the limbic cortex as the bit that looks like a sting ray.

“Limbus” actually means border. This is because the limbic cortex provides a border around the midbrain (as seen in top picture).

The limbic cortex also contains something called the cingulate gyrus (“sing yew lett“). The only tip that I have for remembering this is to perhaps imagine a young, single sting ray down at his local nightclub gyrating his hips in an odd dance in an attempt to attract a mate.

The limbic cortex has an important role in making sure that you avoid negative stimuli. So, you could imagine a string ray who tends to avoid the bigger, stronger males in the nightclub, who might want to pick a fight with him for accidentally hitting on their girlfriend.

sting ray.png
Image credit: Clker.com

The Hippocampus

It’s name translates to “sea horse” because this little guy supposedly looks like  little sea horse in your brain.

This little sea horse sits in your temporal lobe.

His jobs include:

  • moving those short-term memories into the long-term memory (consolidation)
  • spatial navigation (so you remember the way back home after you leave the house…no bread crumbs needed here)
  • context

To remember this, imagine a sea horse who is also a taxi driver. Taxi drivers have to know MILLIONS of routes throughout the area in which they operate. Therefore, they must have good spatial navigation so that they can remember how to get to various places for a for the long-term. They must also be highly attenuated to context, i.e. what’s going on around them, so that they can be safe when out on the road at rush hour.

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Image: seahorse image adapted from cliparthut.com. Car image adapted from canva.com

 

How to remember the components of the limbic system

The limbic cortex is easy to remember – it’s the limbic system so limbic cortex should be straightforward.

As for the rest of the limbic system, try to imagine a generic image of a woman. This generic woman will be used to represent the limbic system.

It is commonly thought that women are more empathetic than men. We’ve already discussed that the amygdala is very important for emotion in the brain. In fact without it, you’d feel a lack of empathy.

Therefore, when we think of the generic woman’s emotive brain, we can link it to the amygdala.

The term “mammillary bodies” literally means “breast shaped”. Therefore, the woman’s breasts can be representative of the mammillary bodies in the limbic system.

The hippocampus can be represented by either the woman’s hips (HIP-pocampus) or by her stomach if you want to imagine a heavier lady (one so heavy that she resembles a HIPPO-campus).

The fornix sounds like the cervix. The cervix is the name given to the lower part of the uterus in a female’s reproductive system. (Stop laughing – this is basic biology!). Thus, the generic woman’s cervix can represent the fornix.

So you should be trying to remember this:

Amygdala.png
Image credit: adapted from MyraethCorax @ DeviantArt.com

 

So when you’re in the exam room and need to remember the components of the limbic system really quickly, simply start at your head and pat your way down your body until you’ve remembered them all  (boys – be imaginative) and don’t forget the limbic cortex!

(I repeat: the weirder, funnier and ruder the image, the better the chance you have of remembering it and more importantly – the information)

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Forebrain: Diencephalon’s structures

Before we move on, let’s remind ourselves of our brain divisions:

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We now know about all the structures in the first subdivision of the forebrain, the telencephalon. Now let’s look at the structures within the second subdivision of the forebrain, the diencephalon.

First things first, you can remember that the diencephalon is the second division of the forebrain because the prefix “di” means “two“, therefore, the diencephalon must come second.

Within the diencephalon, we have the:

  • Thalamus
  • Hypothalamus

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Thalamus

The thalamus is formed of one lobe in each hemisphere – two lobes in total. These two lobes are separated by the massa intermedia.

The thalamus is essentially the brain’s post office. It receives sensory information and sends this to the cortex in a relay. Each nuclei within the thalamus deals with a certain type of sensory information.

The nuclei of the thalamus are:

  • lateral geniculate nucleus
  • medial geniculate nucleus
  • ventrolateral nucleus
Lateral geniculate nucleus-2
Image: eye, shoe and sound icon from canva.com

And the same info as a table:

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So (text version for accessibility):

  • the retina projects visual info to the lateral geniculate nucleus in the thalamus, which then sends it to the primary visual cortex in a relay.
  • the inferior colliculus projects auditory info to the medial geniculate nucleus in the thalamus, which then sends it to the primary auditory cortex in a relay.
  • the globus pallidus, cerebellum and substantia nigra project motor info to the ventrolateral nucleus in the thalamus, which then sends it to the primary motor cortex in a relay.

(If words like “inferior colliculus” are freaking you out – chill! All will be explained soon – just keep reading).

NB: if you’re learning this for an exam – this may be more detailed than you need – just make sure that you definitely know that the thalamus receives sensory information then sends this to the appropriate cortex in a relay.

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Hypothalamus

When thinking about the thalamus and the hypothalamus, I like to think of them as a pair of brothers. The thalamus is the responsible one who has a job as a postman, delivering information to the cortex. Whereas, the hypothalamus is the thalamus’ hormonal teenage brother. 

Hypothalamus’ functions:

  • controls the autonomic nervous system
  • controls the endocrine system

These 2 functions mean two things for the hypothalamus. First of all, let’s start with it’s job of controlling the endocrine system.

For anyone who needs a refresher from GCSE Biology, the endocrine system is the system that controls the release of hormones throughout the body. The hypothalamus does this by having a link to the pituitary gland. The hypothalamus basically tells the pituitary gland which hormones to release.

Think back to your teenage days, specifically, every time your hormones sent you into an irritated, sulky mess. Well, this little guy is the culprit.

Also, every time you get stressed and your heart begins to race and you can’t eat – that’s this little guy’s fault too.

This brings us to his second job, controlling the autonomic nervous system. The autonomic nervous system is the system that kicks in when you’re in a fight or flight scenario, i.e. your heart races, your pupils dilate, your digestion shuts down, etc.

Your autonomic nervous system is switched on via the release of certain hormones (which we’ll discuss more in the blog post on stress).

This means that if the hypothalamus gets all stressed about breaking a nail, it would then tell the pituitary gland to release certain hormones into your bloodstream and next thing you know your heart is racing, adrenaline is surging through your body and you’re feeling  like you’re about to fight a bear.

In summary, it’s good to think of the hypothalamus as a moody, hormonal teenager who overreacts to a lot of things (although all the hypothalamus is trying to do is help you survive). Also, the hypothalamus means “under” which helps the little brother image.

You could also think of the hypothalamus as a primitive ape who reacts in a fight or flight way quickly before rational thinking has change to kick in.

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Midbrain: structures

Again, let’s have a recap:

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Now the midbrain differs from the forebrain and hindbrain as it has no subdivisions. Just remember that the one in the middle doesn’t have subdivisions.

The midbrain or mesencephalon has the following structures:

  • Tectum
  • Tegmentum

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Tectum

This structure is formed of the:

  • Inferior colliculi (singular: inferior colliculus)
  • Superior colliculi (singular: superior colliculus)

Functions:

Screen Shot 2016-07-15 at 22.21.30Screen Shot 2016-07-15 at 22.18.12

To remember the separate functions of each, think of how we as humans have evolved in a way that means that our sense of sight is far more precise than our sense of hearing. We can use our sight to pinpoint the location of a predator, even in low level light. Whereas, our sense of hearing could not accurately tell you the location of a predator.

In this instance it could be argued that the sense of sight is superior to the sense of hearing.

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Tegmentum

This is made up of the:

  • reticular formation
  • periaqueductal grey matter
  • red nucleus
  • substantia nigra

Functions:

Inferior colliculi-5

Bonus-

  • The red nucleus is actually called red due to its high iron content.
  • Damage to the substantia nigra can result in the development of Parkinson’s disease

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Hindbrain: Metencephalon’s structures

Finally, we move onto the hindbrain or the rhombencephalon. The first subdivision of the hindbrain is the metencephalon.

Let’s once again, recap:

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The metencephalon’s structures include:

  • Cerebellum
  • Pons

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Cerebellum (“sair a bell um”)

The cerebellum is the ball-like lump that sticks out at the back of your brain.

Like your cerebrum (main part of your brain), the cerebellum has a left and a right hemisphere. 

The cerebellum is also more densely packed than the cerebral cortex, which means it has more folds (+looks more wrinkly).

Cerebellum’s jobs:

  • Coordination of movement

However, recent studies have found that the cerebellum may also perform these jobs too:

  • timing
  • rhythm
  • cognition
  • attention

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Pons

Pons’ jobs:

  • control of sleep and arousal state
  • carrying info from the cortex to the cerebellum

Pons literally means “bridge” and you can use this to remember how the pons acts as a bridge to allow the information from the cortex to reach the cerebellum.

As for the job of controlling sleep and arousal states, it’s good to note that in psychology “arousal state” just means the state when the participant is alert/awake (I know what you were thinking, you filthy animal).

However, the name pons is similar to the name of the greek god Pan, who was the god of sexuality (amongst other things).

You could use this to answer the question: What is one of the functions of the pons?

Just think pons> Pan > god of sexuality > arousal > arousal state > controlling of arousal state + sleep.

Or perhaps you could imagine the image of a generic greek god and say that this is a god called Pons.

This new greek god is the master of sleep and wakefulness. (Hypnos is actually the greek god of sleep BUT for the purpose of remembering this, we can pretend his name is Pons).

So when you’re asked a question about the pons, think: ah, yes, Pons – the greek god of sleep and wakefulness who controls when people sleep and wake up. Boom.

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Hindbrain: Myelencephalon’s structures

Finally, we arrive at the second division of the hindbrain/rhombencephalon, the myelencephalon.

Let’s have a final recap:

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There’s only one structure within the myelencephalon (and it’s my personal favourite):

  • medulla oblongata

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Medulla oblongata

Jobs of the medulla oblongata:

  • regulating the cardiovascular system
  • regulating respiration
  • regulating skeletal muscle tonus
  • vital reflexes

Going down the list:

Regulating the cardiovascular system

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The cardiovascular system is the system that keeps your heart pumping. This is very important.

Regulating respiration

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Image credit: Clker.com

 

Apologies for echoing the voice of your GCSE Biology teacher but RESPIRATION DOES NOT MEAN BREATHING. Respiration means converting glucose into energy. Energy that you need to go about your daily living. This is also very important.

Regulating skeletal muscle tonus

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Image credit: Clker.com

Skeletal muscle tonus basically refer to ability of the muscles to hold your body/limbs in certain positions. This is also very very important.

Vital reflexes

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Image credit: Clker.com

Every time you: cough, sneeze or vomit, you’ve got this little guy to thank.

Don’t be so ungrateful, this little guy is saving your life every time this happens, as by doing this he stops viruses and other nasties getting into your body. Thanks, Medulla.

To remember the functions of the medulla oblongata we’re going to do a little dance.

  1. Put your hands together over your heart and raise them on and off your chest repeatedly like a heart beating. This represents the regulation of the cardiovascular system.
  2. Now run on the spot. This represents the regulation of respiration (so you have the energy to keep running).
  3. Now stop and flex your muscles. This represents the regulation of skeletal muscle tonus.
  4. Finally, do a big sneeze! This represents the vital reflexes.

Do this on repeat whenever you have a spare moment (you can run through the actions in your head rather than acting them out) and eventually, it’ll stick in your head.

Other medulla info to know:

The medulla oblongata contains gaps. These gaps allow substances to pass through. As mentioned a moment ago, if a toxic substance enters the medulla, good ol’medulla sends out a signal that makes you vomit/sneeze/cough in order to get rid of the nasty toxic substance. What a good guy.

So next time you complain about having a sneezing fit, just remember that that’s your medulla trying to save your life.

Damage to your good guy medulla can result in something called locked-in syndrome. This syndrome includes patients not being able to move their body, apart from their eye muscles.

So look after your good guy medulla. He’s constantly trying to protect your life, after all.

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Phew! You’ve made it to the end of this extra-long post! Here’s a present for your efforts. It’s a hierarchy chart of all the divisions, subdivisions and structures that we just went through.

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Think you’ve got it?

Test yourself here.

Introduction to Neuroanatomy

This post will cover:

  • The nervous system
  • The Brain: basics
  • The corpus callosum
  • Grey matter and white matter
  • chopping brains up
  • protection of the nervous system
  • the ventricular system
  • the blood-brain barriers

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The Nervous System

The nervous system is divided into two main structures:

  1. Central Nervous System (CNS)
  2. Peripheral Nervous System (PNS)

 The Central Nervous System (CNS)

This contains the:

  • Brain 
  • the spinal cord

Screen Shot 2016-06-07 at 22.27.56 The Peripheral Nervous System (PNS)

This structure contains the nerves.

These nerves form two types of pathways:

  • Motor pathways (these go to the muscles)
  • Sensory pathways (these go to the brain)
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Image credit: Taken from Human Body Colouring Book (2015), Amber Books Ltd.

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The Brain: basics

The brain is physically made up of:

  1. Cerebrum (“sair ree brum”)
  2. Cerebellum (“sair a bell um”)
  3. Brain stem

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The cerebrum is the main structure of the brain.

The cerebellum is the ball that sticks out at the back of the brain.

The brain stem is the long stick at the bottom of the brain that hooks the brain up to the spinal cord.

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Brain basics: hemispheres

The brain has two hemispheres, one left hemisphere and one right hemisphere.

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Image credit: Taken from Human Body Colouring Book (2015), Amber Books Ltd.

A lot of brain function is what we call contralateral function.

For example, the left hemisphere controls movement on the right side of the body and vice versa. One hemisphere controls the opposite side of the body. Like when someone contradicts someone else, they take the opposite viewpoint.

If the opposite were true, this would be called ipsilateral function.

This is when one hemisphere controls movement on the same side of the body. For example, if the left hemisphere controlled the left side of the body.

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The Corpus Callosum (“Core pus ka low sum”)

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This is the bundle of fibres that keeps the two hemispheres of the brain connected. It’s name translates to “hard body”.

Any pathway that connects a left and right hemisphere together is known as a commissure.

The corpus callosum is an example of a commissure and is the largest one in your body.

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Grey and white matter

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Image credit: Clker.com

The brain  essentially contains both grey matter and white matter.

Grey matter refers to cell bodies and dendrites.

Whereas, white matter refers to myelinated axons.

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Chopping the brain up

Not saying that you would, but if you were to chop your annoying little brother’s brain in half then you’d have many options on exactly how to cut the brain.

Frontal (transverse/coronal)

Once you’ve somehow extracted his brain, you could give it a frontal cut.

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This is parallel to the forehead.

It’s called a frontal cut because you get to see the brain from the front.

Just to be annoying, some people also refer to it as a coronal cut. You can remember this by thinking about a blade hitting the crown of your head and going straight through (ow!). A coronal cut would be left behind and coronal sounds a little like crown.

Even more annoyingly, some people also refer to it as a transverse cut. (I wish they’d make their mind up!). You can remember that it’s called a transverse cut because transverse means “to extend across something” and a transverse cut extends across the front of the brain.

Screen Shot 2016-06-07 at 22.27.56Sagittal cut 

To perform this cut, you’d send the knife  right between your annoying brother’s eyes and cut his brain straight down the middle. When you’d finished, you’d be able to see one side of his brain (please don’t try this at home).

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Image credit: Taken from Human Body Colouring Book (2015), Amber Books Ltd.

A way to remember this is to think of the star sign Sagittarius. This star sign takes the form of an archer and when archers stand to shoot an arrow, they turn their head to the side. If it helps, sagittal actually translates to “arrow”.

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Image: from computerclipart.com

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This is a cut that is parallel to the ground. Imagine you’ve got your annoying brother pinned to the floor, lying on his stomach with his chin on the carpet. To avoid making a mess and ruining your mum’s cream carpet, you’ll want to make one neat cut through the brain. The best way to do this is to keep your blade paralell to the floor, like you’re cutting the top off of  pumpkin.

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Image credit: Human Body Colouring Book (2015), Amber Books Ltd.

DISCLAIMER: This blog is not responsible for any death or injury. This blog does not condone any violent behaviour. Please do not actually murder your brother, you twit.

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Protection of the nervous system

The brain uses the following to defend itself:

  • ray guns
  • death beams
  • nukes

Okay, that may not be true (please don’t write those on your final exam).

Actually, the brain uses a structure called the Meninges (“men in jees”) to protect itself.

The meninges are formed of 3 layers of tissue. These 3 layers protect the brain and the spinal cord (so, all of the CNS).

The 3 layers of the meninges are called:

  1. Dura Mater  – (Remember it because – it must be Durable to be the top layer of the meninges)
  2. Arachnoid Membrane – (Remember it because- it’s the spider membrane since arachnoid sounds like arachnid)
  3. Pia Mater  – (Remember it because- since its the bottom layer of the meninges, you’d really have to Pia in to get a good look at it!)
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Image source: Antranik.org

Inflammation of the meninges is known as meningitis, which is a deadly illness that you may have heard of.

The meninges float in something called cerebrospinal fluid (CSF). CSF is a clear liquid that fills the subarachnoid space (picture).

CSF’s functions include:

  • shock absorption
  • buoyancy
  • reducing the weight of the brain (so you can actually hold your head up!)

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The Ventricular System

Your brain contains four interconnected structures called ventricles (“ven trik uls”) , which translates to “little bellies”.

These ventricles are all filled with cerebrospinal fluid (CSF).

The ventricular system includes two lateral ventricles, with one in each hemisphere.

This system also contains: a third ventricle, a cerebral aqueduct and a fourth ventricle.

These can all be seen here:

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This picture shows the production and movement of CSF within the ventricular system:

1. A membrane known as the choroid plexus filters the blood to produce CSF (the black dots).png

 

Here’s the same information again in a list format for those who prefer lists:

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Here’s the process again in plain text with ways to remember the steps:

 

  • A membrane known as the choroid plexus filters the blood to produce CSF.

Remember this because: the choroid plexus sounds like your solar plexus which is located in the pit of your stomach/gut. Your gut also does a lot of filtering when it filters out the waste products from the food that you eat.

Therefore, just think – choroid plexus – sounds like solar plexus – gut – the gut filters stuff – the choroid plexus filters blood into CSF!

 

  • This CSF is then stored in the lateral ventricles.

Remember this because: you can picture the lateral ventricles like a pair of testicles – there’s a left one and a right one. The difference being that, where the testicles store sperm cells until it’s needed, the lateral ventricles store CSF until it’s needed.

 

  • The CSF then travels down into the third ventricle.

  • Then through the cerebral aqueduct.

  • Then through the fourth ventricle and finally travels down the spinal cord.

Remember this because: sticking with the testicles analogy (because that’s certainly going to stick in your mind), the third ventricle, cerebral aqueduct and fourth ventricle can be thought of as being like the shaft of a penis (stay with me here).

In a penis, when the sperm cells are needed they travel from the testicles, where they are being stored, down through the shaft.

Similarly, in the ventricular system, when the CSF is needed, it travels from the lateral ventricles, where it is being stored, down through the third ventricle, cerebral aqueduct and fourth ventricle.

(Remember – the weirder and ruder the analogy – the more likely it is to stick in your mind!)

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Why does this happen though?

The purpose of the ventricular system is to carry waste away from the brain (and down the spinal cord into the rest of your body…ew!).

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The Blood-Brain Barrier

These are semipermeable barriers. Permeable means “lets stuff through” – so semipermeable means that they only let SOME stuff through.

Blood-brain barriers allow lipid soluble substances (fat soluble, substances that dissolve in fat) to pass through as they wish.

However, substances with LARGE MOLECULES aren’t allowed to pass through easily and must be actively transported through the walls instead.

Imagine the blood-brain barriers are all nightclub owners. They are also all jerks. They only let small skinny substances (small lipid soluble substances) to pass through their doors into their club.

They don’t let larger substances (with larger molecules) to pass freely through them and into the club.

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Instead, any substances with larger molecules must be actively transported past the barrier. In the jerky club owner analogy, you can think of this as that the larger substances must offer the jerk blood-brain barrier a bribe, in order to get past and be “actively transported” into the club. Trust me, the weirder/funnier the analogy is, the easier it’ll be to remember!

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Image source: molecule image from Clker.com

They are similar to capillaries in the rest of your body however, unlike those, blood-brain barriers do not contain gaps.

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But why are the blood-brain barriers such jerks?

Well they keep out larger substances to:

  • Maintain a stable environment
  • To give protection from dangerous chemicals

(like a bouncer does when he keeps violent people out of the club to maintain a somewhat nice environment inside)

…so maybe they aren’t such jerks after all!

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Think you’ve got it?

Test yourself here.

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(Image credit for image of frontal brain cut: “Human brain frontal (coronal) section: #24 is lateral sulcus” by John A Beal, PhD Dep’t. of Cellular Biology & Anatomy, Louisiana State University Health Sciences Centre Shreveport. No copyright intended. Used in accordance with the CC-BY 2.5 license. Disclaimer: I do not own this image.)

(Image credit: Amber Books Ltd.)

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