When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob. Describe how.

The arrival of a nerve impulse at a synapse causes Ca2+ channels to open (1 mark). Ca2+ ions enter the presynaptic knob by facilitated diffusion (1 mark). The presence of Ca2+ ions causes synaptic vesicles to fuse with the presynaptic membrane and the subsequent release of neurotransmitter into the synapse (1 mark).