Psychology

Sensory (afferent) neurons carry information from receptors to the CNS; motor (efferent) neurons carry commands from the CNS to muscles/glands; interneurons connect neurons within the CNS and process information.

Once the membrane reaches threshold (about -55 mV), an action potential fires at full amplitude; a stronger stimulus does not produce a larger spike. Stimulus intensity is coded by firing frequency, not spike size.

Depolarization: voltage-gated Na+ channels open and Na+ rushes in. Repolarization: Na+ channels inactivate and voltage-gated K+ channels open, letting K+ flow out. K+ efflux briefly overshoots, causing hyperpolarization.

The action potential 'jumps' between Nodes of Ranvier rather than propagating continuously, greatly speeding conduction. It is enabled by the myelin sheath, which insulates the axon between nodes.

Oligodendrocytes myelinate axons in the central nervous system; Schwann cells myelinate axons in the peripheral nervous system.

It prevents a new action potential or limits firing rate. The absolute refractory period (Na+ channels inactivated) prevents any new spike; the relative refractory period (membrane hyperpolarized) requires a stronger-than-normal stimulus.