Chapter 6: Electrophysiology of the Cell Membrane

The action potential is then dissected into its components: the rapid depolarization phase driven by voltage-gated sodium channel opening, the peak of membrane potential reversal, and the repolarization phase mediated by sodium channel inactivation and potassium channel activation. Critical principles including the all-or-none law, threshold potential, and absolute and relative refractory periods establish how neurons generate stereotyped electrical responses that propagate reliably over long distances. The chapter explores conduction velocity in both unmyelinated and myelinated axons, emphasizing how saltatory conduction along myelinated fibers dramatically increases transmission speed by allowing action potentials to jump between nodes of Ranvier. The cable properties of axons—including membrane resistance, membrane capacitance, and longitudinal axial resistance—are presented as fundamental determinants of how electrical signals decay and propagate through neural tissue. Throughout the discussion, clinical applications connect ionic mechanisms to pathological conditions such as multiple sclerosis, which disrupts myelin and impairs conduction, and channelopathies, which result from genetic or acquired dysfunction of ion channels and compromise cellular excitability. By integrating ionic physiology with macroscopic neural signaling, this chapter establishes the mechanistic foundation for understanding how excitable tissues generate, transmit, and regulate electrical signals underlying sensation, motor control, and neural computation.