6.5 Synaptic transmission

Question 1

What are cholinergic synapses?

Answer 1

Synapses that use the neurotransmitter acetylcholine (ACh)

Question 2

What happens during synaptic transmission?

Answer 2

• Depolarisation of pre-synaptic membrane causes voltage-gated calcium ion channels to open
• Ca2+ diffuse into pre-synaptic knob
• Causing vesicles containing ACh to fuse with the presynaptic membrane
• Releasing ACh into the synaptic cleft
• ACh diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane
• Causing sodium ion channels to open
• Na+ diffuse into post-synaptic neurone, causing depolarisation
• If threshold is reached an action potential is triggered

Question 3

What happens to ACh after synaptic transmission?

Answer 3

• Hydrolysed by acetylcholineesterase
• Products are reabsorbed into presynaptic knob
• To prevent overstimulation

Question 4

Spatial summation

Answer 4

Neurotransmitter from many presynaptic neurones combine to reach threshold, triggering an action potentail

Question 5

Temporal summation

Answer 5

Neurotransmitter from one presynaptic neurone is released many times over a short period combine to reach threshold, triggering an action potential

Question 6

How does inhibition occur?

Answer 6

• Inhibitory neurotransmitters hyperpolarise postsynaptic membrane
• As Cl- channels open and Cl- diffuses in
• So inside of neurone has a more negative charge than outside
• So more Na+ required for depolarisation
• Reducing likelihood of threshold being reached

Question 7

Cholinergic synapse

Answer 7

Neurone to neurone
Receptors on postsynaptic membrane
No clefts
Neurotransmitters can be excitatory or inhibitory
Action potential many be initiated in postsynaptic neurone

Question 8

Neuromuscular junction

Answer 8

Motor neurone to muscle
(More) receptors on muscle fibre sarcolemma
Clefts to store enzymes to break down neurotransmitter
Neurotransmitters always excitatory
Action potential propagates along sarcolemma