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An action potential is the electrical signal that travels down an axon when a neuron receives a sufficiently strong stimulus. This impulse operates on an all-or-none principle, meaning it either fires completely or not at all. The propagation of the signal involves the movement of sodium (Na+) and potassium (K+) ions across the neuronal membrane.

Action Potential

The all-or-none phenomenon is related to an action potential in the way that once a neuron's membrane potential gets to the threshold of excitation, the neuron will either fire an action potential all the way or not at all (i.e., there can't be any "partial" firing of a neuron). 

All-or-None Phenomenon in Action Potential of Neuronal Communication

A graph of an action potential demonstrates the specific millivolt (mV) changes across a neuron's membrane during different signaling phases. The process begins at a resting potential of roughly -70mV. Upon reaching the threshold of excitation at approximately -55mV, the neuron fires, causing a spike to a peak action potential of 30mV. As the cell recovers, it undergoes repolarization (dropping to around 5mV) and then hyperpolarization, where the charge dips to roughly -80mV before eventually returning to its baseline resting state.

Action Potential Diagram

A neuron's membrane has just received a stimulus strong enough to trigger an electrical impulse. Which of the following statements best breaks down the sequence of ion movements that allows this impulse to travel along the axon?

During the action potential, the electrical charge across the membrane changes dramatically. The millivolts through the phases are approximately -70mV at resting potential, -55mV at threshold of excitation, 30mV at peak action potential, 5mV at repolarization, and -80mV at hyperpolarization.

Action Potential Voltage Phases

The action potential is an electrical signal that typically moves from the cell body down the axon to the axon terminals.

Action Potential Propagation

When the action potential arrives at the terminal button, the synaptic vesicles release their neurotransmitters into the synaptic cleft.

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