Organisms Respond To Changes In The Environment

Question 1

Synaptic transmission

Answer 1

1: An action potential arrives at the presynaptic neurone, which opens voltage-gated sodium channels inside the synaptic knob.
2: Sodium ions diffuse into the synaptic knob, which leads to an action potential inside the synaptic knob.
3: Voltage-gated calcium channels open. Calcium ions diffuse into the synaptic knob, which causes synaptic vesicles to move down the synaptic knob.
4: Synaptic vesicles fuse with the presynaptic membrane, which leads to acetylcholine being released into the synaptic cleft.
5: Acetylcholine diffuses across the synaptic cleft, where it binds to receptor sites on sodium channels, causing them to open.
6: Sodium ions diffuse into the postsynaptic neurone, which leads to an action potential inside the postsynaptic neurone.
7: Acetylcholinesterase breaks down acetylcholine into choline and ethanoic acid.
8: Choline and ethanoic acid are taken back into the presynaptic neurone, where they’re recombined to form acetylcholine.
9: Acetylcholine is transported into synaptic vesicles using ATP.