Q.Why is transmission across a chemical synapse unidirectional, while transmission across an electrical synapse is essentially instantaneous and can occur in either direction?

[!TLDR] Chemical synapses are one-way because vesicles/neurotransmitter exist only presynaptically and receptors only postsynaptically; electrical synapses are near-instant because current flows directly through gap junctions with no chemical step. [!ANSWER] Chemical synapse: unidirectional because vesicles are only presynaptic and rece …

A chemical synapse is unidirectional because the machinery needed to release neurotransmitter — the synaptic vesicles — is present only in the presynaptic terminal, and the receptor proteins that respond to that neurotransmitter are present only on the postsynaptic membrane; there is no equivalent mechanism running in reverse, so the signal can only pass from presynaptic to postsynaptic cell. An electrical synapse, by contrast, connects the two cells' cytoplasm directly through gap-junction channels, so ionic current can in principle flow through those same channels in either direction, and because no vesicle release, diffusion or receptor binding step is n …

Think about which structural components exist on only one side (chemical) versus both si …

Do not claim all electrical synapses are always bidirectional in practice — some are functionally biased by channel properties — but structurally the pathway itself permits cur …