Explain the all-or-nothing principle for an action potential.

In the resting state, the membrane potential of a neuron is around -70 millivolts (mV). When acted upon by a stimulus, the membrane depolarises as Nagated ion channels open and allow sodium ions to rush into the axon, making the membrane potential more positive. An action potential occurs when the membrane depolarises to a certain threshold, if this threshold is not reached the action potential will not be triggered. This is referred to as the all-or-nothing principle in biology: it means that the power of a stimulus is not proportional to the power of the action potential. In simpler terms, the action potential will either occur or it won't, it will not be a graded response. 

Example: The resting potential of a neuronal membrane is -70 mV, and the threshold for the action potential is -55 mV. If a stimulus depolarises the membrane to -65 mV, the action potential won't occur, as it hasn't passed the threshold. However, if another stimulus can depolarise the membrane -40 mV, which is above the threshold, this will trigger the action potential.

Answered by Oyku C. Biology tutor

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