15.6 - Transmission Across A Synapse

Question 1

What is a cholinergic synapse, and what neurotransmitter does it use?

Answer 1

A cholinergic synapse is a type of synapse where the neurotransmitter is acetylcholine, which is composed of acetyl (ethanoic acid) and choline.

Question 2

Where are cholinergic synapses commonly found?

Answer 2

Cholinergic synapses are common in vertebrates, occurring in the central nervous system and at neuromuscular junctions (junctions between neurones and muscles).

Question 3

What triggers the process of neurotransmitter release in a cholinergic synapse?

Answer 3

The arrival of an action potential at the presynaptic neurone causes calcium ion protein channels to open, allowing calcium ions (Ca²⁺) to enter the synaptic knob via facilitated diffusion.

Question 4

What happens after calcium ions enter the presynaptic neurone?

Answer 4

The influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft.

Question 5

How does acetylcholine travel across the synaptic cleft, and what does it do next?

Answer 5

Acetylcholine diffuses quickly across the narrow synaptic cleft due to the short diffusion pathway and binds to receptor sites on sodium ion protein channels in the postsynaptic neurone membrane.

Question 6

What is the result of acetylcholine binding to receptor sites on the postsynaptic membrane?

Answer 6

Binding opens sodium ion protein channels, allowing sodium ions (Na⁺) to diffuse rapidly into the postsynaptic neurone along a concentration gradient.

Question 7

What is generated in the postsynaptic neurone after sodium ions diffuse in?

Answer 7

The influx of sodium ions generates a new action potential in the postsynaptic neurone.

Question 8

How is acetylcholine removed from the synaptic cleft, and why is this important?

Answer 8

Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid, which diffuse back to the presynaptic neurone for recycling. This prevents continuous action potential generation, ensuring discrete signal transmission.

Question 9

What happens to the choline and ethanoic acid after being recycled?

Answer 9

ATP from mitochondria is used to recombine choline and ethanoic acid into acetylcholine, which is then stored in synaptic vesicles for future use.

Question 10

What happens to sodium ion protein channels in the postsynaptic membrane in the absence of acetylcholine?

Answer 10

Sodium ion protein channels close when acetylcholine is not present in the receptor sites.