Unit 2 The Biological Approach

Content CNS, genes, neurotransmitters and hormones

Focus – Stress

The role of the Central Nervous System and Neurotransmitters in human

behaviour.

We start by examiningWe start by examining

The Nervous System has 2 main parts – the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)

The CNS consists of the brain, the spinal cord and nerve cells. (neurones)

Neurones are cells that receive and

transmit messages, passing them

from cell to cell.

The brain is protected within the skull and the spinal cord is protected within the vertebrae.

The CNS is essentially the BRAIN

consider the importance of the brain

We need to understand that the brain is ‘localised’ ‘localised’ – meaning different areas do different things

The brain is also ‘lateralised’ ‘lateralised’ –

meaning the left and right hemispheres are slightly different

Parts of the brain and spinal cordParts of the brain and spinal cordClick here>>> to check out the brain tutorial

The Brain

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...

Sperry clip 123

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

Learn some more about the CNS Neurotransmitters and the CNS

Don’t sit there passively – make notes…how many neurones? How many connections? etc.

Neurotransmitters

Neurotransmitters are chemical messengers chemical messengers that act between the neurones in the brain. This allows the brain to process thoughts and memories.

Neurones receive and transmit messages, passing them from cell to cell.

DopamineDopamineSerotoninSerotoninnoradrenalinenoradrenaline

How Synapses work

You need to be able to explain how messages are passed via neurotransmitters

One moreanimation

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!

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.

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/reuptakeSo 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.

Neurotransmitters continued:

RECEPTORS can be thought of as locks – if a certain chemical (neurotransmitter) fits like a key, then the message is passed on: if it does not fit then the message is blocked.

Draw a diagram to illustrate a synapse

Place the following in the correct order p4 Bio pack The dendrites of one neurone are close to the terminal buttons of

another neuron but in between there is a synaptic gap

Each neuron has a cell body If the neurotransmitter is taken up it will trigger an electrical

impulse in the cell body, which then travels down the neurons axon so that the message continues

The receptors on the dendrites of the nearby cell either receive the neurotransmitter (a chemical) if it ‘fits’, or they don’t if it does not ‘fit’

From the cell body an axon leads down to terminal buttons that hold neurotransmitters in synaptic vesicles and from the cell body there are also dendrites on the end of which are receptors

An electrical impulse travels down the axon and releases the neurotransmitter into the gap

If the neurotransmitter is not taken up by the nearby cell the message is stopped

Manufactured drugs work in the synapse

they are made to mimic neurotransmitters, they more or less fit certain receptors and are received like neurotransmitters.

Some drugs block the message – they fit the receptor, so the natural neurotransmitter cannot pass the message on because the receptor is not available.

Summary

How neurones work in the CNS

This is an interesting site that will add to your understandingof the brain http://outreach.mcb.harvard.edu/

animations/synaptic.sw

To end the session on the CNSand the Brain