Which principle states that a neuron either fires completely or does not fire at all?

The principle that indicates a neuron either fires completely or does not fire at all is known as the all-or-none response. This concept is fundamental to our understanding of neural signaling. When a neuron reaches a certain threshold level of depolarization, typically due to the influx of sodium ions, it will fire an action potential, transmitting a signal along the axon.

If the stimulus does not reach this threshold, the neuron will not fire; it does not fire partially. This binary response is crucial for ensuring clear and effective communication between neurons. The all-or-none response ensures that the signal transmitted is consistent in magnitude and intensity, regardless of how much above the threshold the stimulus is.

Other concepts related to neuron firing, like depolarization and action potential, describe aspects of the firing process but do not embody the principle that defines the complete versus non-firing state. Similarly, threshold potential is the specific point at which the all-or-none response is triggered, but it does not encompass the overarching principle that a neuron either fires fully or not at all.