13.5 Synapses

Question 1

Why are synapses important?

Answer 1

• prevent impulses travelling in wrong direction
• allow different neurones to communicate
• convergence
• divergence

Question 2

What is convergence (in neurones)?

Answer 2

Impulses from multiple neurones passed onto one neurone.

Question 3

What is divergence (in neurones)?

Answer 3

Impulse from one neurone is passed on to more than one neurone.

Question 4

What synapse specifically do you need to know about?

Answer 4

Cholinergic synapse

Question 5

Describe the structure of a presynaptic neurone.

Answer 5

Smooth endoplasmic recticulum
Synaptic vesicles
Ca+ ion channels
Mitochondria

Question 6

Describe the structure of the post synaptic neurone.

Answer 6

Na+ ion channels

Question 7

What do synaptic vesicles contain?

Answer 7

Neurotransmitters

Question 8

What two categories of synapse are there?

Answer 8

Excitatory
Inhibitory

Question 9

What is the gap between the presynaptic and post synaptic neurone called?

Answer 9

Synaptic cleft

Question 10

What does the smooth endoplasmic reticulum do in the presynaptic neurone?

Answer 10

Produces vesicles (containing neurotransmitters)

Question 11

When do the Na+ ion channels open?

Answer 11

In the presence of neurotransmitters

Question 12

What is an excitatory neurone?

Answer 12

Results in the depolarisation of post synaptic neurone.

Question 13

What is an inhibitory neurone?

Answer 13

Synapses which stop an action potential being set up in post synaptic neurone by causing hyper polarisation.

Question 14

How is an impulse transmitted across a synapse? (8 marks)

Answer 14

Action potential arrives at synaptic knob
Ca2+ ions channels open & Ca2+ ions diffuse into synaptic knob
Exocytosis
Neurotransmitters diffuse across the synaptic cleft to the post synaptic membrane
Neurotransmitters bind with specific receptors on post synaptic membrane
Sodium channels open and sodium ions diffuse into post synaptic neurone
Post synaptic membrane is depolarised
Action potential generated in post synaptic membrane
Synaptic knob repolarised
Neurotransmitters broken down in post synaptic neurone

Question 15

Why is the impulse only transmitted one way?

Answer 15

Only the presynaptic neurone produces neurotransmitters
Only the post synaptic neurone has receptors for neurotransmitters
Only the post synaptic neurone has calcium ion channels

Question 16

In some synapses , the amount of neurotransmitters from a subtle impulse is not enough to trigger an action potential, so the impulse can be transmitted due to summation. What is summation?

Answer 16

Build up of neurotransmitters, until the threshold is reached for an action potential to be generated.

Question 17

What is spatial summation?

Answer 17

Multiple presynaptic neurones release neurotransmitters to one post synaptic neurone, to reach the threshold.

Question 18

What is temporal summation?

Answer 18

Several action potentials over a short period of time, release lots of neurotransmitters , these build up, and reach the threshold.

Question 19

How can a drug/chemical stimulate synapses to create more action potentials?

Answer 19

Inhibit enzyme that breaks down neurotransmitters
Drug binds in place of neurotransmitters (drug isn’t broken down)
Stops neurotransmitters from being absorbed

Question 20

How do painkillers work?

Answer 20

Block channels from opening in post synaptic neurone,
this inhibits the production of action potentials