nerve impulses and synapses

Question 1

Describe the sequence of events involved in transmission across a cholinergic synapse (5)

Answer 1

1. Depolarisation/AP of presynaptic membrane;
2. Calcium channels open and calcium ions enter (synaptic knob);
3. (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine
4. Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
5. (Acetylcholine attaches) to receptors on the postsynaptic membrane;
6. Sodium ions enter (postsynaptic neurone) leading to depolarisation;

Question 2

following release of acetylcholine into a neuromuscular junction, a muscle contraction occurs.

describe the sequence of events following the release of acetylcholine that leads to stimulation of this contraction (4)

Answer 2

1. Acetylcholine diffuses across synaptic cleft
2. Acetylcholine attaches to receptors on post synaptic membrane/ sarcolemma
3. Sodium ions enter leading to depolarisation
4. Calcium ions released by sarcoplasmic reticulum

Question 3

give 3 similarities between cholinergic synpase and a neuromuscular junction

Answer 3

• both use acetylcholine
• both use the Na/K pump to repolarise the axon
• both use acetylcholinesterase
• both cause Na+ ion influx on binding of acetylcholine to receptor

Question 4

give 3 differences between a cholinergic synapse and a neuromuscular junction

Answer 4

• NJ only motor neruones, CS sensory, motor, relay
• NJ connects neurone to muscle fibre, CS connects neurone to neurone or neurone to effector
• NJ only excitatory, CS excitatory or inhibatory
• NJ acetylcholine binds to receptors on muscle fibre membrane, CS acetylcholine binds to receptors on post synaptic nuerone membrane
• NJ end of neural pathway no further AP, CS forms AP in post synaptic neurone