CNS and PNS

Striatum

The striatum is involved in controlling thought and action

It is also involved in registering rewarding events

Hippocampus

The hippocampus is involved in memory – people with hippocampus damage often suffer from amnesia

It seems to be particularly involved in learning about spaces – London cab drivers have enlarged hippocampi

Corpus Callosum

The corpus callosum is a bundle of neurons that links the two brain hemispheres, which are otherwise largely separated

Some treatments for epilepsy involved cutting the corpus callosum, which had some very interesting side-effects...

Amygdala

The amygdalae play a primary role in processing emotions and in remembering emotional events

The amygdalae are particularly linked to the emotion of fear

Hypothalamus

One function of the hypothalamus is in thermoregulation – it serves as a thermostat for the body

It also serves other homeostatic functions

Specific areas of the hypothalamus are associated with hunger and satiety

Neurotransmission

Overview of neurotransmission1. Action potential (electrical impulse) passed

down presynaptic neuron

2. Vesicles move to the edge of synaptic button

3. Vesicles dump neurotransmitter into synapse

4. Neurotransmitter is taken up by receptors on postsynaptic neuron

5. Postsynaptic neuron is either encouraged to ‘fire’ or not to fire

6. Neurotransmitter in synapse is either broken down or transported back into presynaptic neuron

Action potential

Now the presynaptic neuron has a signal.

This stimulus is transmitted as an action potential electrically down the neuron until it gets to the bulge in the picture, the synaptic button.

Vesicles

But the electrical signal cannot just bounce on to the next neuron. There’s too much space in between the two neurons.

The change in potential is going to affect little vesicles, little blobs of membrane inside the presynaptic neuron. These vesicles contain the neurotransmitters, which are synthesized in the presynaptic cell, and stored in the vesicles until stimulated.

The synapse

So what are we looking at here?

That blue bulbous portion that looks like a nose is the presynaptic neuron.

The smiley below it in pink is the postsynaptic neuron.

And neurotransmission is what gets a signal from one side to the other.

The distance between a presynaptic and postsynaptic neuron is about 20-40 nanometers!

Into the synapse

The electrical signal (via its effects on calcium ions) causes the vesicles to begin to migrate to the cell membrane.

Then they either dump all of their neurotransmitter into the synapse or just release a little of it.

Reception

So now the neurotransitting chemicals are in the synapse. They float across the tiny space in a random way, and in the process, bump into receptors on the other side.

The receptors here are important. This is because there tend to be many different types of receptor for one type of neurotransmitter.

Depending on which receptor type the neurotransmitter hits, the result will usually be either excitation or inhibition of the postsynaptic neuron’s action potential.

Breakdown/reuptake

So what happens then? You don’t want to leave the neurotransmitter sitting around in the synapse. Because this means it will continue to bump into receptors and pass signals on to the post-synaptic neuron.

So the signal must be terminated.

Depending on the neurotransmitter you’re dealing with, there are various things that can happen.

An enzyme can break down the neurotransmitter chemical into its component parts, or the presynaptic neuron can have transporters, which suck the neurotransmitter up back into the synaptic button, either to be shoved back into vesicles, or to be degraded.