3.6.2.2 Synaptic transmission

Question 1

How do synapses ensure that nerve impulses are unidirectional?

Answer 1

The neurotransmitters bind to the receptors which are only found on the postsynaptic membranes.

Question 2

Give one way that neurotransmitters are removed from the synaptic cleft.

Answer 2

Neurotransmitters are broken down by an enzyme, and the products are re-absorbed by the presynaptic neurone.

Question 3

Which neurotransmitter do you find at cholinergic synapses?

Answer 3

Acetylcholine (ACh)

Question 4

Why are calcium ions important in synaptic transmission?

Answer 4

The influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane.

Question 5

What do inhibitory neurotransmitters do at synapses?

Answer 5

Inhibitory neurotransmitters hyperpolarise the postsynaptic membrane, preventing it from firing an action potential.

Question 6

What kind of receptors are found at neuromuscular junctions?

Answer 6

Nicotinic cholinergic receptors

Question 7

Myasthenia gravis is a disease in which the body’s immune system gradually destroys receptors at neuromuscular junctions. This leads to weaker muscular responses than normal.
Explain why.
[3 marks]

Answer 7

• There will be fewer receptors for acetylcholine (ACh) to bind to,…
• …so fewer sodium ion channels will open at neuromuscular junctions,…
• …making it less likely that action potentials will be generated in the muscle cells.

Question 8

Galantamine is a drug that inhibits the enzyme acetylcholinesterase (AChE).
Predict the effect of galantamine at a neuromuscular junction and explain your answer.
[3 marks]

Answer 8

• Galantamine would stop acetylcholinesterase (AChE) breaking down acetylcholine (ACh), so there would be more ACh in the synaptic cleft…
• …and it would be there for a longer period of time.
• This means more nicotinic cholinergic receptors would be stimulated.