13.5 Synapses

Question 1

What must an impulse do to reach the central nervous system or an effector?

Answer 1

Be passed between several neurones

Question 2

What is the name of the junction between two neurones?

Answer 2

A synapse

Question 3

What are neurotransmitters?

Answer 3

The chemicals that are used to transmit impulses across a synapse

Question 4

What is the name for the chemicals that are used to transmit impulses across a synapse?

Answer 4

Neurotransmitters

Question 5

What is a synaptic cleft?

Answer 5

The gap separating the axon from the dendrite of 2 neurones

Question 6

What is a presynaptic neurone?

Answer 6

The neurone along which the impulse has travelled

Question 7

What is a postsynaptic neurone?

Answer 7

A neurone that receives the neurotransmitter

Question 8

What is a synaptic knob?

Answer 8

The swollen end of the presynaptic neurone

Question 9

What does the synaptic knob contain?

Answer 9

Many mitochondria, endoplasmic reticulum and vesicles

Question 10

Why does the synaptic knob contain mitochondria and endoplasmic reticulum?

Answer 10

To make neurotransmitters

Question 11

What is a synaptic vesicle?

Answer 11

A vesicle containing neurotransmitters

Question 12

What are neurotransmitter receptors?

Answer 12

Receptor molecules which the neurotransmitter binds to in the postsynaptic membrane

Question 13

What are neurotransmitter receptors specific to?

Answer 13

Each individual neurotransmitter

Question 14

What are the two types of neurotransmitter?

Answer 14

Excitatory and inhibitory

Question 15

What do excitatory neurotransmitters result in?

Answer 15

The depolarisation of the post-synaptic neurone, by helping to trigger action potential

Question 16

Give an example of an excitatory neurotransmitter.

Answer 16

Acetylcholine

Question 17

What do inhibitory neurotransmitters result in?

Answer 17

The hyperpolarisation of the post-synaptic membrane, preventing an action potential

Question 18

Give an example of an inhibitory neurotransmitter.

Answer 18

G.A.B.A

Question 19

Describe the process of the transmission of impulses across synapses. (long answer)

Answer 19

1- Action potential reaches the end of the presynaptic neurone
2- Depolarisation of the presynaptic membrane causes calcium ion channels to open
3- Calcium ions diffuse into the presynaptic knob
4- This causes synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane. Neurotransmitter is released into the synaptic cleft by exocytosis
5- Neurotransmitter diffuses across the synaptic cleft and binds with its specific receptor molecule on the postsynaptic membrane
6- This causes sodium ion channels to open
7- Sodium ions diffuse into the postsynaptic neurone
8- This triggers an action potential and the impulse is propagated along the postsynaptic neurone

Question 20

What happens to the neurotransmitter once it has triggered an action potential in the post synaptic neurone?

Answer 20

It is removed from the cleft and taken back in by the pre-synaptic neurone

Question 21

How is acetylcholine broken down?

Answer 21

By the enzyme acetylcholinesterase

Question 22

What is acetylcholine broken down into?

Answer 22

Acetic acid (or ethanoic acid) and choline

Question 23

What does acetyclholinesterase do?

Answer 23

Catalyses breakdown of acetylcholine and releases it from the receptors on the post-synaptic membrane.

Question 24

What does removing the neurotransmitter from the synaptic cleft prevent?

Answer 24

The response happening again, and allows the neurotransmitter to be recycled

Question 25

What are cholinergic synapses?

Answer 25

Synapses that use the neurotransmitter acetylcholine

Question 26

What is a neuromuscular junction?

Answer 26

Where a motor neurone and a muscle cell meet

Question 27

What happens if a neurotransmitter reaches the receptors on a muscle cell?

Answer 27

It will cause the muscle cell to contract

Question 28

When acetylcholine is broken down, what type of reaction is it?

Answer 28

Hydrolysis

Question 29

Where is acetylcholinesterase located?

Answer 29

On the receptors of the sodium ion channel on the postsynaptic membrane

Question 30

Where are the breakdown products of acetylcholinesterase taken?

Answer 30

Back to the presynaptic knob

Question 31

How is acetylcholine reformed?

Answer 31

Reformed from acetic acid and choline using ATP released by mitochondria in the presynaptic neurone

Question 32

Where is acetylcholine stored?

Answer 32

In the vesicles of the presynaptic neurone

Question 33

What are the roles of synapses?

Answer 33

- Ensure impulses are unidirectional - Allow an impulse from one neurone to be transmitted to a number of neurones, at multiple synapses - Allows for many neurones to feed into the same synapse

Question 34

What is summation?

Answer 34

The build up of neurotransmitters in a synapse to sufficient levels to trigger an action potential

Question 35

What are the two types of summation?

Answer 35

Spatial and temporal summation

Question 36

What is spacial summation?

Answer 36

When a number of presynaptic neurones connect to one postsynaptic neurone

Question 37

What is temporal summation?

Answer 37

When a single presynaptic neurone releases neurotransmitters as a result of an action potential several times over a short time period