Final answer:
The first event in action potential generation is the opening of voltage-gated sodium channels at the axon hillock, initiating depolarization and nerve signal transmission.
Step-by-step explanation:
Of the events listed, the one that occurs first during action potential generation is A. Voltage-gated sodium channels open at the axon hillock. This initiates the action potential by allowing sodium (Na) ions to rush into the neuron, causing depolarization of the membrane. This depolarization will then propagate along the axon as more sodium channels open in response to the positive charge spreading inside the cell membrane, leading to a wave of depolarization which is essential for nerve signal transmission.
The opening of voltage-gated sodium channels is essential as it marks the beginning of the action potential. This is followed by a sequence of events, including the opening of potassium channels and eventual repolarization and hyperpolarization of the neuron. Only after these events, will calcium influence neurotransmitter release at the synaptic junction.