2.10.7 Synapses

Question 1

Do Neurones come into direct contact with each other?

Answer 1

No

Question 2

Where the dendrites of two neurones meet, what happens?

Answer 2

a junction known as a synapse is formed

Question 3

At a synapse, there is a very small gap between neurones, what is the gap called?

Answer 3

This very small gap is known as the synaptic cleft or synaptic gap

Question 4

Why can’t electrical impulses travel directly from one neuron to the next

Answer 4

due to the synaptic cleft (electricity cannot ‘jump’ the gap)

Question 5

Instead, the electrical signal is briefly converted to a chemical signal that can cross the synaptic cleft, what is the chemical called?

Answer 5

The chemical signaling molecules used to transfer the signal between neurones at a synapse are known as neurotransmitters

Question 6

Once these neurotransmitters cross the synaptic cleft and meet the neurone on the opposite side, what happens?

Answer 6

the signal is converted back into an electrical impulse, which can then pass along the neurone

Question 7

The electrical impulse travels along, what?

Answer 7

first axon (of the first neurone, known as the presynaptic neurone)

Question 8

This triggers the end of the presynaptic neurone to release chemical messengers called, what?

Answer 8

neurotransmitters from vesicles

Question 9

What do the vesicles do?

Answer 9

These vesicles fuse with the presynaptic membrane, releasing their contents into the synaptic cleft

Question 10

The neurotransmitters diffuse across, what?

Answer 10

the synaptic cleft and bind with receptor molecules on the membrane of the second neurone (known as the postsynaptic membrane)

Question 11

the second neurone generates an electrical impulse after the neurotransmitters diffuse across the synaptic cleft and bind with receptor molecules on the membrane of the second neurone, where does it then travel?

Answer 11

then travels down the second axon

Question 12

What happens after the electrical impulse travels down the second axon?

Answer 12

The neurotransmitters are then destroyed to prevent continued stimulation of the second neurone (otherwise the neurotransmitters would cause repeated impulses to be sent)

Question 13

Synapses ensure that impulses only travel, where?

Answer 13

in one direction, avoiding the confusion that would be caused within the nervous system if impulses were able to travel in both directions

Question 14

Exam Tip

Answer 14

For maximum marks, you will need to understand the structure and functioning of a synapse and explain what happens at each step.

Exam questions about neurotransmitters are a good opportunity for examiners to introduce unfamiliar examples and contexts, so remember the following:

Neurotransmitters move by diffusion – remember, this requires a concentration gradient and is a passive process

Receptors that are complementary in shape to neurotransmitters are located on the postsynaptic neurone

Drugs (such as heroin, ecstasy and cocaine) can bind to neurotransmitter receptors, triggering impulses in different regions of the brain