Which of the following is NOT a stage of action potential?

The process of an action potential involves a series of stages that are critical for the transmission of electrical signals along neurons. The stages typically include polarization, depolarization, and hyperpolarization.

During the polarized stage, the neuron is in a resting state, with a negative charge inside compared to the outside. When the neuron is stimulated, it undergoes depolarization, where sodium channels open, allowing sodium ions to rush into the cell, leading to a reversal of the membrane potential. Following depolarization, the neuron can enter a state of hyperpolarization, where the membrane potential becomes more negative than its resting state, making it less likely to fire another action potential immediately.

In contrast, neurotransmitter release refers to a different process that occurs at the synapse, where the electrical signal (action potential) is converted into a chemical signal to communicate with other neurons. This process does not occur during the action potential itself but rather follows it, marking the communication phase between neurons. Therefore, neurotransmitter release is not a stage of the action potential, distinguishing it from the other listed stages.