Ions, membrane potentials, and myelin

Abstract

The neuron is uniquely suited for the transmission of electrical impulses. The neuronal membrane itself allows for charge separation; depending on the permeability of the membrane to a given type of ion, that ion will distribute across the membrane, producing a resting membrane potential, described by the Nernst equation. However, via the sodium-potassium (Na-K) pump, an active electrochemical gradient is maintained across the cell membrane, the magnitude of which can be calculated by knowing the relative concentrations of all the relevant ions, both in the intracellular fluid (ICF) and extracellular fluid (ECF), via the Goldman-Hodgkin-Katz equation. The development of action potentials are dependent on the presence of voltage-gated sodium channels, which open when the membrane itself is partially depolarized through mechanical, electrical, or chemical means. The initiation of an action potential creates a spreading area of voltage change, causing additional nearby channels to open, ultimately leading to the propagation of the action potential down the entire length of the axon. Myelin dramatically speeds the process of neuronal depolarization by producing salutatory conduction. Together, with the complex set of processes at the neuromuscular junction, neural transmission is effectively achieved. © 2007 Humana Press Inc.