Q.Describe the sequence of events by which a nerve impulse is transmitted across a chemical synapse, from the arrival of the impulse at the presynaptic terminal to the generation of a new impulse in the postsynaptic neuron.

[!TLDR] Impulse reaches the presynaptic terminal → Ca2+ channels open → Ca2+ influx → synaptic vesicles release neurotransmitter → it diffuses across the cleft and binds postsynaptic receptors → opens ion channels → generates a new potential in the postsynaptic cell. [!ANSWER] Depolarization → Ca2+ entry → vesicle …

When the nerve impulse arrives at the presynaptic axon terminal, it depolarizes the terminal membrane, which opens voltage-gated Ca2+ channels; Ca2+ flows in from the extracellular fluid. The rise in intracellular Ca2+ causes synaptic vesicles loaded with neurotransmitter to fuse with the presynaptic membrane and release their contents into the synaptic cleft by exocytosis. The neurotransmitter molecules diffuse across the narrow cleft and bind to specific receptor proteins on the postsynaptic membrane; this binding opens ion channels there, producing either an excitatory or an inhibitory change in the postsynaptic membrane's potential. Finally the neurotransmitter is cleared from the cleft (enzyma …

Walk through the sequence strictly in order: electrical signal (presynaptic) → chemical signal (clef …

Do not omit the Ca2+ step — vesicle release is triggered specifically by Ca2+ influx, not dir …