The diagram below shows a cholinergic synapse affected by a neurotoxin called neurexin-B. Neurexin-B selectively blocks the voltage-gated calcium ion channels on the presynaptic membrane, preventing them from opening when an action potential arrives.
Which of the following is the direct consequence of this block on synaptic transmission?
Synaptic vesicles are unable to fuse with the presynaptic membrane to release neurotransmitter.
The postsynaptic membrane remains permanently depolarised due to trapped calcium ions in the synaptic cleft.
Neurotransmitter cannot bind to receptors on the postsynaptic membrane because the active sites are blocked.
Acetylcholine is broken down prematurely by acetylcholinesterase before it can reach the postsynaptic receptors.