Abstract

The nerve axons and muscle fibers exhibit the property of excitability by which they can transmit signals along their membranes. At rest, potential differences develop across the unit membranes owing to differences in the concentration of ions and their selective permeability towards specific ions.

Graphical Abstract

Description of the graphic: The exchange of ions and establishment of the resting membrane potential (a). Application of stimulus and generation of action potential (b). Graphical representation of action potential in nerve axonal membrane (c)

S. Jana (K)

Department of Veterinary Physiology, West Bengal University of Animal & Fishery Sciences, Kolkata, West Bengal, India

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023

37

P. K. Das et al. (eds.), Textbook of Veterinary Physiology, https://doi.org/10.1007/978-981-19-9410-4_3

Keywords

Resting membrane potential ∙ Action potential ∙ Polarized state ∙ Depolarization ∙ Repolarization

Learning Objectives

• Ionic basis of resting membrane potential (RMP) in a neuronal membrane.

• Generation of action potential and its phases.

• Characteristics of action potential.

• Basis of refractoriness in the neuronal membrane after the action potential.

• Factors that determine the propagation and conduction velocity of action potential.

Every cell of the body has electrical potentials across its cell membranes. Additionally, some cells such as the nerve axons and muscle fiber exhibit the property of excitability by which they are able to transmit signals along their membranes. The excitability or rapid changes in electrochemical impulses exhibited by certain cells of the body is governed by the principles of membrane theory or ionic hypothesis. The the­ory is based on the ability of the cellular membrane to respond to changes in the membrane permeability to ions. The membrane theory states that potentials develop across the unit membranes owing to differences in the concentration of ions and their selective permeability towards specific ions. The understanding of the fundamentals of nerve cell excitability are based on the finding by Hodgkin and Huxley (1952) whose experiments with the squid giant axons gave the first insights into the generation of action potential and the kinetics of ion channels. The membrane potential is an essen­tial feature of all body cells both excitable and non-excitable. Recent studies highlight the indispensable role of membrane potentials in regulating several important functions of the body such as the biological rhythms; specifically the circa­dian rhythm. It denotes the events that repeat cyclically over 24 h period and is coordinated by the superior chiasmatic nucleus of the hypothalamus. The depolarization and a con­sequent fall in action potential firing lead to changes in the membrane potential of neurons in the superior chiasmatic nucleus. Contrary to the popular belief, here depolarization leaves the cell membrane less excitable leading to a decrease in action potential generation. The pineal glands respond to these changes by secreting melatonin which mediates the cyclic events. The membrane potential is essential for various sensory perceptions such as vision, hearing, taste, and olfac­tion. The neuroendocrine cells of the body located in the hypothalamus, pituitary, thyroid gland, and pancreas are excitable and secrete hormones that regulate basic body functions. The excitability of neuroendocrine cells is driven by action potential which occurs as rapid oscillation bursts induced by Ca⁺ ions influx followed by a period of rest. This depolarization due to calcium ion influx leads to the secretion of hormones from the concerned cell types.

3.1