Synapse

Neurons do not touch. A tiny gap, the synaptic cleft, separates them. An electrical message cannot jump this gap on its own. So a chemical carries it across:

• The message reaches the axon ending of the first neuron.
• The ending releases a chemical messenger, a neurotransmitter such as acetylcholine.
• The chemical crosses the cleft and starts a new message in the dendrites of the next neuron.

Only axon endings hold the chemical. So a message crosses a synapse in one direction only.

A small example

Think of a relay race where runners cannot touch. The first runner throws the baton across a small gap. The second catches it and runs on. The baton is acetylcholine, and the gap is the synaptic cleft.

Where marks go

The 2025 ICSE Biology paper asked for four terms in the order a message travels. The answer is dendrites, cyton, axon ending, synaptic cleft. In CISCE's report on the 2025 Biology paper, examiners note confusion over where the axon ending and the synaptic cleft go. The ending comes first; the gap comes after it.

The 2027 specimen paper asks for the chemical stored in axon endings. Its answer is acetylcholine, so learn to spell it. Spelling is one of the ways marks slip away on answers you know.

About the author

Deepti Sardana

Founder Member & Academic Lead

An IIT alumna (M.Sc., M.Phil.) with over 25 years in teaching, child psychology and learning assessment. As Academic Lead at EduBrahma, she leads the method TRUtesting uses to find where and why a child loses marks.

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