Q.Distinguish between a chemical synapse and an electrical synapse with respect to the mode of impulse transmission across them.

[!TLDR] Electrical synapses pass current directly through gap junctions (fast, near-instant); chemical synapses release a neurotransmitter across a cleft that binds postsynaptic receptors (slightly slower, one-way). [!ANSWER] Electrical synapse = direct ionic current flow through gap junctions; chemical synapse = neurotransmitter release across a synaptic cleft acting on receptors.

At an electrical synapse, the presynaptic and postsynaptic membranes are connected by gap-junction channel proteins that allow ionic current to pass directly from one cell's cytoplasm to the next, without any chemical intermediary; transmission is therefore almost instantaneous. At a chemical synapse, the two membranes are separated by a synaptic cleft with no direct cytoplasmic connection, and the signal must cross by the release of a chemical neurotransmitter from the presynaptic terminal, its diffusion across the cleft, and its binding to receptors on the postsynaptic membrane — a process that, while still very fast, takes measurably longer (a 'synaptic delay') than transmission at an electrical synapse. Chemical synapses are far more common than electrical synapses in the human nervous system. [!ANSWER] Electrical synapse: direct current flow via gap junctions, near-instantaneous. Chemical synapse: neurotransmitter release + diffusion + receptor binding across a cleft, with a small synaptic delay.

Ask whether the two membranes are directly connected (electrical) or separated by a gap that needs a chemical messenger to cross (chemical).

Do not assume chemical synapses are slow in absolute terms — the delay is only a fraction of a millisecond, just measurably longer than an electrical synapse.