Explain how a nerve impulse passes from one neurone to the next across a synapse.

When a nerve impulse reaches the axon terminal of the presynaptic neuron, voltage‑gated Ca²⁺ channels open and Ca²⁺ enters the cell, triggering vesicles to fuse with the membrane and release neurotransmitter into the synaptic cleft.
The neurotransmitter molecules diffuse across the narrow synaptic cleft.
They bind to specific receptors on the postsynaptic membrane, opening ion channels.
The resulting ion flux depolarises the postsynaptic membrane, generating a new action potential.
The myelin sheath on the axon, by insulating the membrane, increases the speed of impulse conduction via saltatory conduction.