Explain how a nerve impulse is passed across a synapse.

1. 1 · Define the synapse. A synapse is the junction between the axon terminal of one neuron and the dendrite of the next. The two do not touch.
2. 2 · Draw the synapse. [Diagram: synaptic knob with vesicles, synaptic cleft, dendrite of the next neuron, arrow for direction]
3. 3 · Explain the steps.
   • The impulse reaches the synaptic knob.
   • A neurotransmitter (acetylcholine) is released into the synaptic cleft.
   • It acts on the next dendrite and starts a new impulse.
   • The flow is one way: axon to dendrite.
4. 4 · Link to daily life. A dentist's local anaesthetic stops pain impulses, so you feel no pain.
5. 5 · Close. So the message is electrical inside a neuron and chemical across the synapse.

Scoring tip: Use the words 'electrical' and 'chemical' clearly. Examiners look for both.