Unit 2 The Biological Approach Content CNS, genes, neurotransmitters and hormones Focus – Stress

We start by examining The role of the Central Nervous System and Neurotransmitters in human behaviour.

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 4

We need to understand that the brain is ‘localised’ – meaning different areas do different things The brain is also ‘lateralised’ – meaning the left and right hemispheres are slightly different

Parts of the brain and spinal cord Click here>>> to check out the brain tutorial See I Learn for Brain tutorial

Striatum The striatum is involved in controlling thought and action It is also involved in registering rewarding events 7

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 8

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 1 2 3 9

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 10

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 11

Learn some more about the CNS Neurotransmitters and the CNS Don’t sit there passively – make notes…how many neurones? How many connections? etc. D group up to here – no correlation gap fill though

Neurotransmitters Dopamine Serotonin noradrenaline Neurotransmitters are 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. Dopamine Serotonin noradrenaline Students label the diagram in their pack

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

One more animation

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! 16

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. 17

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. 18

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. 19

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. 20

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. 21

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 understanding of the brain http://outreach.mcb.harvard.edu/animations/synaptic.sw

To end the session on the CNS and the Brain