For which ion does an influx occur during the second stage of an action potential, facilitating neurotransmitter release?

During the second stage of an action potential, also known as the depolarization phase, the significant influx of ions that facilitates neurotransmitter release is primarily due to calcium ions (Ca2+). When an action potential reaches the axon terminal of a neuron, it causes voltage-gated calcium channels to open. The resulting influx of Ca2+ ions into the presynaptic terminal is critical for triggering the process of exocytosis, which is the release of neurotransmitters into the synaptic cleft.

Calcium plays a pivotal role in this process because it binds to specific proteins in the presynaptic membrane that facilitate the fusion of synaptic vesicles containing neurotransmitters with the membrane itself. This fusion is an essential step for the release of neurotransmitters into the synaptic cleft, allowing communication between neurons.

While sodium ions (Na+) are crucial during the initial depolarization phase of the action potential and potassium ions (K+) are involved in repolarization, they do not directly mediate neurotransmitter release at the synapse. Magnesium ions (Mg2+) are more commonly associated with stabilizing cellular structures or influencing neuronal excitability rather than being directly involved in neurotransmitter release.

Thus, the influx of Ca2+