Question 1
Multiple choiceEasy1 markWhen an impulse reaches a neuron terminal, the presynaptic membrane depolarizes and neurotransmitter is released. Which ion movement acts as the intracellular signal for this release?
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Answer: C. Depolarization of the presynaptic membrane causes Ca²⁺ uptake into the neuron. Ca²⁺ acts as a signalling chemical inside the neuron and promotes neurotransmitter release. A: confuses K⁺ efflux, associated with repolarization, with the signal for neurotransmitter release. B: confuses Na⁺ influx, associated with depolarization, with the ion that signals release. D: reverses the direction: Ca²⁺ enters rather than leaves the presynaptic neuron. Remember: Ca²⁺ entry at the presynaptic membrane signals neurotransmitter release.