Synapse

In the syllabus and the exam

Synapse questions test whether candidates understand that a nerve impulse cannot jump directly from one neuron to the next as an electrical signal, and must instead be converted into a chemical signal to cross the gap. A complete answer explains that an impulse arriving at the end of one neuron causes vesicles to release neurotransmitter into the synaptic gap, the neurotransmitter diffuses across and binds to receptors on the next neuron's membrane, and this triggers a new electrical impulse to begin in that neuron, after which the neurotransmitter is broken down or reabsorbed. Exam questions often ask candidates to explain why impulses can only travel in one direction across a synapse, and the expected reasoning is that neurotransmitter and its receptors are located on only one side of the gap in each direction, acting like a one-way valve. Candidates frequently omit the reabsorption or breakdown step, which markers look for as evidence the response is not continuous and unlimited.

Example

At a synapse, an arriving nerve impulse triggers the release of neurotransmitter that diffuses across the gap to the next neuron.

Related terms

NeuronReflex actionStimulus

Source:SRC-DSKP-EN