Describe the process of generation and conduction of nerve impulses in humans. Add a note on saltatory conduction.
Nerve impulses, also called action potentials, arise when the resting membrane potential of a neuron, about minus seventy millivolts, is depolarized enough by a stimulus to reach threshold, often around minus fifty five millivolts. This event opens voltage gated sodium channels, producing a sudden influx of sodium ions that reverses the membrane potential into the positive range. Soon after, sodium channels inactivate and voltage gated potassium channels open, permitting potassium ions to exit, which drives repolarization toward the resting state. A short hyperpolarization phase may follow before the sodium potassium pump restores ionic balance. Action potentials propagate along the axon without decrement. In unmyelinated axons, conduction is continuous, with the signal regenerated at successive sites. Myelinated axons conduct by saltatory conduction. The myelin sheath insulates the axon, forcing current to flow at Nodes of Ranvier, where sodium channels cluster. This arrangement accelerates transmission, conserves energy, and enables rapid neural communication.
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