How does a nerve impulse cross a synapse?

A nerve impulse crosses a synapse when a chemical neurotransmitter diffuses across the gap and triggers a new impulse in the next neurone.

GCSE Biology

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

In more detail

When an electrical impulse reaches the end of a neurone, it causes a chemical (neurotransmitter) to be released into the synapse (the tiny gap between neurones). The neurotransmitter diffuses across the gap and binds to receptors on the next neurone. This triggers a new electrical impulse in that neurone, so the signal continues.

Key points for the exam

  • Impulse arrives → neurotransmitter released into the synapse.
  • Neurotransmitter diffuses across the gap.
  • It binds to receptors on the next neurone → a new impulse starts.
Exam tip: Name the three steps — release, diffuse, bind to receptors — and note that the signal becomes chemical then electrical again.

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