Question

why is the action potential necessary for the release of neurotransmitters?
a) voltage - gated ca²⁺ ion channels need to open, causing ca²⁺ ion influx and fusion of the synaptic vesicles with the membrane releasing the neurotransmitter
b) the influx of cl⁻ ions causes the synaptic vesicles to dissolve and release neurotransmitters
c) voltage - gated k⁺ ion channels open and the k⁺ ion outflow causes neurotransmitters to diffuse across the synaptic cleft
d) the k⁺/na⁺ ion pump maintains the resting membrane potential which causes neurotransmitters to move out of the cells through osmosis

Explanation:

When an action potential reaches the axon terminal, it depolarizes the membrane. This depolarization causes voltage - gated \(Ca^{2+}\) ion channels to open. The influx of \(Ca^{2+}\) ions triggers the fusion of synaptic vesicles (containing neurotransmitters) with the presynaptic membrane, leading to neurotransmitter release.

• Option b is incorrect because \(Cl^{-}\) ion influx is not involved in neurotransmitter release in this way.
• Option c is incorrect as \(K^{+}\) outflow is mainly related to repolarization of the neuron during an action potential, not neurotransmitter release.
• Option d is incorrect because the \(K^{+}/Na^{+}\) pump maintains the resting membrane potential, and neurotransmitter release is not through osmosis but exocytosis triggered by \(Ca^{2+}\).

Answer:

A. Voltage - gated \(Ca^{2+}\) ion channels need to open, causing \(Ca^{2+}\) ion influx and fusion of the synaptic vesicles with the membrane releasing the neurotransmitter.