Action Potential

• An action potential, also known as a nerve impulse, is a rapid and temporary change in the electrical potential across the cell membrane of a neuron.
• It serves as the primary means of transmitting information within the nervous system.
• Action potentials are all-or-nothing events, meaning they either occur with full amplitude or not at all, and they propagate without decrement along the axon.

Here is a detailed explanation of the different phases of an action potential in the context of the nervous system:

Resting state:

• Neuron is not actively transmitting signals; resting membrane potential is around -70 mV.

Stimulus and depolarization:

• External stimulus cause local depolarization. If threshold (-55 mV) is reached, voltage-gated Na+ channels open, causing further depolarization and membrane potential to rise.

Repolarization:

• Voltage-gated Na+ channels close, and voltage-gated K+ channels open, allowing K+ ions to exit the cell, causing the membrane potential to decrease (repolarize) back towards resting state.

Hyperpolarization and after-hyperpolarization:

• K+ channels may remain open slightly longer, causing an overshoot of the membrane potential, leading to temporary hyperpolarization before returning to resting level.

Refractory period:

• Neuron enters a period where it is difficult or impossible to generate another action potential; divided into absolute and relative refractory periods to ensure unidirectional propagation of action potentials along the axon.

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