14 - Origin of Resting Membrane Potentials

Abstract

The structural and chemical composition of the cell membrane is examined in this chapter and correlated with the properties of resistance and capacity of the membrane. The chapter also discusses most of the factors that determine or influence the resting membrane potential (Em) of cells. It is mentioned that to understand the mode of action of therapeutic drugs, toxic agents, neurotransmitters, hormones, and plasma electrolytes on the electrical activity of nerve and muscle, it is necessary to understand the electrical properties and behavior of the cell membrane at rest and during excitation. Some drugs and toxins exert primary or secondary effects on the electrical properties of the cell membrane and thereby exert effects, for example, on automaticity, arrhythmias, and force of contraction of the heart. The cell membrane exerts tight control over the electrical activity and the contractile machinery during the process of excitation-contraction (electromechanical) coupling. Passive electrical properties of the cell membrane discuss membrane structure and composition, membrane capacitance and resistivity, membrane fluidity, potential profile across membrane. Maintenance of ion distributions includes resting potentials and ion distributions, Na+ and K+ distribution and the Na+-K+ pump, CI- distribution, Ca2+ distribution. Equivalent electrical circuit, Nernst equation, concentration cell, activity coefficient, Nernst-Planck equation, energy wells, half-cell potentials are discussed under equilibrium potentials. Electrochemical driving forces and membrane ionic currents include electrochemical driving forces, and membrane ionic currents. The factors that determine the intracellular ion concentrations in cells are examined here. The mechanism whereby the ionic distributions give rise to diffusion potentials and the factors that determine the magnitude and polarity of each ionic equilibrium potential has been discussed. Also the factors that determine the magnitude and polarity of each ionic equilibrium potential has been described. The electrogenic pump potential has physiological importance in cells. The electrogenic pump potential may also affect automaticity of the nodal cells of the heart as well as other types of cells that exhibit automaticity.