Question

When an action potential arrives at the end of the axon terminal, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. Select the answer that correctly describes the primary stimulus for vesicles to move toward the cell membrane and eventually release their contents.

A. Axonal Ca+2 is increased because endoplasmic reticulum voltage-gated calcium channels open and Ca+2 enters the cytoplasm.
B. Voltage-gated channels open, and K+ exits to the extracellular fluid, decreasing intracellular K+.
C. Voltage-gated membrane channels open, and multiple types of ions enter the cytoplasm, increasing the intracellular positive charge.
D. Voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium.

Answer 1

The correct answer is D. An influx of Ca2+ ions due to the opening of voltage-gated calcium channels is the primary stimulus for the movement of vesicles towards the membrane and the release of neurotransmitters at the axon terminal.

Step-by-step explanation:

The primary stimulus for vesicles to move toward the cell membrane and release their contents in an axon terminal is D. Voltage-gated membrane channels open, and Ca2+ enters the cytoplasm, increasing intracellular calcium. When an action potential arrives at the axon terminal, it triggers the depolarization of the membrane, which in turn causes voltage-gated Na+ channels to open. Na+ ions enter the neuron, further depolarizing the membrane and subsequently leading to the opening of voltage-gated Ca2+ channels. The influx of Ca2+ ions is crucial because they bind to proteins on the surfaces of synaptic vesicles, leading the vesicles to merge with the presynaptic membrane and undergo exocytosis. This process releases the neurotransmitter into the synaptic cleft.