Synaptic transmission

Question 1

What is a synapse?

Answer 1

The junction between a neurone and another neurone or between a neurone and an effector

Question 2

What is a synaptic cleft?

Answer 2

The tiny gap between the cells at a synapse

Question 3

What is a presynaptic neurone?

Answer 3

The neurone before the synapse

Question 4

What is a post synaptic neurone?

Answer 4

The neurone after the synapse

Question 5

What is a synaptic knob?

Answer 5

A swelling on the pre-synaptic neurone

Question 6

Where are synaptic vesicles found and what do they contain?

Answer 6

In the synaptic knob

Neurotransmitter

Question 7

What is the effect of an action potential on a synapse?

Answer 7

When an action potential reaches the end of a neurone, it causes neurotransmitters to be released into the synaptic cleft.
They diffuse across to the post synaptic membrane and bind to specific receptors.
When neurotransmitters bind to receptors, they might trigger an action potential and cause muscle contraction or cause a hormone to be secreted

Question 8

How are impulses unidirectional?

Answer 8

The receptors are only on the post synaptic membrane

Question 9

Why are neurotransmitters removed from the cleft and how?

Answer 9

To prevent the reaction from keep happening

Taken back into the presynaptic neurone and broken down by enzymes and products taken into the neurones

Question 10

What are cholinergic synapses?

Answer 10

Synapses which use acetylcholine

Question 11

What happens when an action potential arrives at the synaptic knob of the presynaptic neurone?

Answer 11

The action potential stimulates voltage-gated calcium ion channels in the presynaptic neurone to open, causing calcium ions to diffuse into the synaptic knob and are pumped out by active transport after

Question 12

What does the influx of calcium ions into the synaptic knob cause?

Answer 12

The synaptic vesicles to fuse with the presynaptic membrane and the vesicles release the neurotransmitter acetylcholine into the synaptic cleft by exocytosis

Question 13

What happens when ACh diffuses across the synaptic cleft?

Answer 13

It binds to specific cholinergic receptors on the post synaptic membrane, causing sodium ion channels in the post synaptic neurone to open.

Question 14

What does the influx of sodium ons into the post synaptic membrane cause?

Answer 14

Depolarisation

Question 15

What does the depolarisation of the post synaptic membrane cause?

Answer 15

An action potential is triggered if the generator potential reaches the threshold level.
ACh is removed from the synaptic cleft

Question 16

What enzyme breaks down acetylcholine?

Answer 16

Acetylcholinesterase

Question 17

What are the two types of neurotransmitter?

Answer 17

Excitatory

Inhibitory

Question 18

What do excitatory neurotransmitters do?

Answer 18

Depolarise the post synaptic membrane, increasing the chance of an action potential being fired if threshold is reached

Question 19

What do inhibitory neurotransmitters do?

Answer 19

Hyperpolarise the postsynaptic membrane, preventing an action potential from being fired

Question 20

What is an inhibitory synapse?

Answer 20

A synapse where inhibitory neurotransmitters are released from the presynaptic membrane

Question 21

What is summation?

Answer 21

The effect of neurotransmitters released from many neurones or one thats stimulated a lot in a short period of time, is added together

Question 22

What are the two types of summation?

Answer 22

Spatial

Temporal

Question 23

Why does summation happen?

Answer 23

If there is only a weak stimulus, it may not cause enough neurotransmitter to be released to excite the postsynaptic membrane to the threshold level and stimulate an action potential

Question 24

What is spatial summation?

Answer 24

Two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone

Question 25

What is temporal summation?

Answer 25

Two or more nerve impulses arrive in quick succession from the same presynaptic neurone

Question 26

What is a neuromuscular junction?

Answer 26

Specialised cholinergic synapse between a motor neurone and a muscle cell

Question 27

What neurotransmitter does a neuromuscular junction use?

Answer 27

Acetylcholine

Question 28

What differences are there between a neuromuscular junction and a normal cholinergic synapse?

Answer 28

At a neuromuscular junction;

• The post synaptic membrane has lots of folds that form clefts, clefts store AChE
• The postsynaptic membrane has more receptors than other synapses
• ACh is always excitatory so when a motor neurone fires an action potential, it normally triggers a response in a muscle cell

Question 29

What effects can the use of drugs have on synapses?

Answer 29

• some are the same shape as neurotransmitters so they mimic their action at receptors causing more to be activated
• Some block receptors so they cant be activated by neurotransmitters
• Some inhibit the enzyme that breaks down neurotransmitters
• Some stimulate the release of neurotransmitter from the presynaptic neurone so more receptors are activated
• Some inhibit the release of neurotransmitters from the presynaptic neurone so fewer receptors are activated §

Question 30

What are antagonist drugs?

Answer 30

Drugs that block receptors so they cant be activated by neurotransmitters

Question 31

What are agonist drugs?

Answer 31

Drugs that are the same shape as neurotransmitters so they mimic their action at receptors