Synapses

Question 1

What is the presynaptic neurone?

Answer 1

The neurone along which the impulse has arrived

Question 2

What is the postsynaptic neurone?

Answer 2

The neurone that receives the neurotransmitters

Question 3

What is the synaptic cleft?

Answer 3

The gap which separates the pre and postsynaptic neurones

Question 4

What is the synaptic knob?

Answer 4

The swollen end of the the presynaptic neurone

Question 5

Why does the synaptic knob have many mitochondria and endoplasmic retitculum?

Answer 5

To enable it to manufacture neurotransmitters

Question 6

What are synaptic vesicles?

Answer 6

Vesicles containing neurotransmitters, that fuse with the presynaptic membrane and release their contents into the synaptic cleft

Question 7

What are neurotransmitter. receptors?

Answer 7

Receptors that the neurotransmitters bind to in the postsynaptic membrane

Question 8

What are the two types of neurotransmitters?

Answer 8

Excitatory and inhibitory

Question 9

What are excitatory neurotransmitters?

Answer 9

Neurotransmitters that result in the depolarisation of the postsynaptic membrane. This causes an action potential to be triggered

Question 10

What is an example of an excitatory neurotransmitter?

Answer 10

Acetylcholine

Question 11

What are inhibitory neurotrasmitters?

Answer 11

Neurotransmitters that result in the hyperpolarisation of the postsynaptic membrane. This prevents an action potential from being triggered

Question 12

When the action potential reaches the end of the presynaptic neurone, what happens?

Answer 12

The depolarisation of the presynaptic membrane causes calcium ion channels to open, and calcium ions to diffuse into the presynaptic knob

Question 13

What happens once calcium ions diffuse into the presynaptic knob?

Answer 13

It causes synaptic vesicles containing neurotransmitters to fuse to the presynaptic membrane, causing neurotransmitters to be released into the synaptic cleft

Question 14

What happens once the neurotransmitters have been released into the cleft?

Answer 14

They bind with specific receptors on the postsynaptic neurone

Question 15

What happens once the neurotransmitters bind to the receptors on the postsynaptic neurone?

Answer 15

This causes sodium ion channels to open, so sodium ions diffuse into the postsynaptic neurone; this depolarisation triggers an action potential

Question 16

In what synapses is acetylcholine used?

Answer 16

Across cholinergic synapses

Question 17

What happens to acetylcholine once the action potential has been triggered in the postsynaptic neurone?

Answer 17

It is hydrolysed into choline and ethanoic acid

Question 18

What enzyme is used in the hydrolysation of acetylcholine?

Answer 18

Acetylcholinesterase

Question 19

Why is the hydrolysation of acetylcholine important?

Answer 19

It allows it to be recycled and prevents it from continuously generating a new action potential

Question 20

How is acetylcholine recycled?

Answer 20

Once it has been hydrolysed, the ethanoic acid and choline diffuse back into the presynaptic neurone, where ATP recombines it into acetylcholine

Question 21

Why are synapses important?

Answer 21

• Ensure impulses are unidirectional

- Allow an impulse from one presynaptic neurone to be transmitted to multiple postsynaptic neurones (and visa versa)

Question 22

How do synapses ensure impulses are unidirectional?

Answer 22

Neurotransmitter receptors are only present on the postsynaptic neurone

Question 23

What is summation?

Answer 23

Where the amount of neurotransmitter from one impulse is not enough to result in an action potential, so the amount of neurotransmitter needs to build up sufficiently

Question 24

What is spatial summation?

Answer 24

This occurs when a number of presynaptic neurones connect to one postsynaptic neurone; each releases neurotransmitters which together is enough for an action potential

Question 25

What is temporal summation?

Answer 25

This occurs when a single presynaptic neurone releases neurotransmitters several times over a short period; this builds up in the synapse until the quantity is sufficient enough for an action potential