The all-or-none principle states that

Answer 1

In the simplest sense, the all-or-none principle of neuronal firing means that a neuron will either fire or it won't, there is no "half" firing. When a neuron receives excitatory input, its sodium (Na) channels open and allow Na to flow into the cell, depolarizing it (a resting neuron has a membrane potential of -65mV relative to extracellular fluid outside the cell). Once the neuron has been sufficiently excited above some threshold (typically -55mV), the cell fires, or sends an action potential down its axon to its terminal button. This electrical signal causes a series of chemical actions within the cell which results in neurotransmitters being released from the cell, to be picked up by other neurons. As long as a neuron reaches the threshold, it will always result in a large influx of Na ions, bringing the membrane potential to about +40mV, which will propagate down the cell as an action potential. If the neuron does not reach this threshold, it will not depolarize or create an action potential.

Answer 2

The all-or-none principle states that if a stimulus surpasses threshold amount, the action potential is the same. It was created by the American physiologist Henry P. Bowditch in 1871.