(a)[2]
Name the structures at A and B.
(b)[3]
Explain what is meant by saltatory conduction and describe its effect on the transmission of a nerve impulse.
(c)[5]
The sea snail Conus purpurascens produces a toxin that blocks calcium ion channels in the presynaptic knob of a cholinergic synapse. As a result, no action potentials occur in the postsynaptic neurone. Explain why the presence of this toxin results in no action potentials in the postsynaptic neurone.