What event triggers action potential in a neuron?

The triggering of an action potential in a neuron occurs when the membrane is depolarized to a specific threshold level. This is a crucial physiological process in which the neuron's membrane potential changes in response to stimuli. When the neuron receives sufficient excitatory signals, the voltage-gated sodium channels open, allowing sodium ions to flood into the cell. This influx of positively charged ions further depolarizes the membrane, which can lead to the generation of an action potential if the threshold is reached.

In contrast, while binding of neurotransmitters to receptors plays an essential role in initiating the process of depolarization, it is the subsequent depolarization that actually triggers the action potential. Maintaining the resting potential is vital for a neuron's ability to generate action potentials, but it does not directly trigger one. Reuptake of neurotransmitters is involved in neurotransmission regulation after the signal has occurred, but it does not contribute to the initiation of an action potential. Therefore, the event that directly leads to the initiation of an action potential is the depolarization of the membrane to threshold.