3.6.2.2 synaptic transmission

Question 1

What is the myelin made up of?

Answer 1

Schwann cells

Question 2

What is saltatory conduction?

Answer 2

In myelinated neurones, depolarisation can only occur at the nodes of Ranvier, so the impulse ‘jumps’ from node to node.

Question 3

What are the nodes of Ranvier?

Answer 3

Bare areas of neurones that are not insulated with myelin.

Question 4

Give three factors that affect the speed of conduction of action potentials.

Answer 4

1. Axon diameter
2. Myelination
3. Temperature

Question 5

Why does increasing temperature increase the speed of transmission?

Answer 5

Ions diffuse faster when temperature increases.

Question 6

Give one function of the refractory period

Answer 6

It produces discrete impulses that are unidirectional.

Question 7

What is a synapse?

Answer 7

The junction between a neurone and the next cell.

Question 8

What ensures that impulses cross the synapse in one direct only?

Answer 8

Neurotransmitter is released from the presynaptic knob.

Receptors for the neurotransmitter is only found on the post synaptic membrane.

Question 9

What are Cholinergic synapses?

Answer 9

Synapses that use acetylcholine.

Question 10

What happens to the neurotransmitter once they have attached to the receptors on the post synaptic membrane?

Answer 10

They are broken down by enzymes and their products are taken back into the neurone.

Question 11

What stimulates the synaptic vesicles to move towards the presynaptic membrane in a cholinergic synapse?

Answer 11

Calcium ions diffuse into the synaptic knob causing the synaptic vesicles to move towards the presynaptic membrane.

Question 12

What happens when the acetylcholine bind with the receptors on the post synaptic membrane?

Answer 12

Sodium channels open and sodium flood in. If the threshold is reached and action potential is generated.

Question 13

How is acetylecholine removes from the synaptic cleft?

Answer 13

Acetylcholinesterase breaks acetylcholine and the products are reabsorbed to make more acetylcholine.

Question 14

What is temporal summation?

Answer 14

It is where there are two or more nerve impulses that arrive in quick succession from the same presynaptic membrane and action potential is more likely to occur..

Question 15

What is spatial summation?

Answer 15

When many neurones connect to one neurone. The small amount of neurotransmitter released from each of these neurones can be enough to reace the threshold value.

Question 16

ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.

Answer 16

1. Releases relatively small amount of energy / little energy lost as heat;
2. Releases energy instantaneously;
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from / does not leave cells.

Question 17

Describe how calcium ions are involved in synaptic transmission.

Answer 17

(Nerve impulse causes) Ca2+ to enter presynaptic neurone/membrane;

(Ca2+ entry) causes fusion of vesicles with presynaptic membrane /
causes exocytosis / release of transmitter;

Question 18

Describe how a nerve impulse causes the release of neurotransmitter from the vesicles in the presynaptic knob

Answer 18

1. (Nerve impulse/depolarisation of membrane) causes Ca2+channel (proteins) to open;
2. Ca2+enter by (facilitated) diffusion;
3. Causes (synaptic) vesicles to fuse with (presynaptic) membrane;

Question 19

GABA causes negatively charged chloride ions to enter post synaptic neurones - How does this inhibit post synaptic neurones?

Answer 19

1. neurone becomes more negative/hyperpolarised
2. not enough sodium ions enter (to reach threshold)
3. for depolarisation to take place