Neuron & Action Potential

The electrical language of the nervous system

Neurons maintain a resting membrane potential of −70 mV due to the Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in) and selective ion permeability. An action potential is triggered when a stimulus depolarizes the membrane to threshold (≈−55 mV). Voltage-gated Na⁺ channels open rapidly → Na⁺ rushes in → membrane depolarizes to +40 mV. Na⁺ channels then inactivate while K⁺ channels open → K⁺ rushes out → repolarization and brief hyperpolarization (refractory period). The action potential propagates down the axon; myelination creates saltatory conduction (jumping between nodes of Ranvier), dramatically increasing speed (up to 120 m/s in myelinated vs 0.5 m/s in unmyelinated). Multiple sclerosis involves myelin sheath degradation.