5 - Excitable tissues

Abstract

Publisher Summary This chapter discusses the properties of excitable tissues. All cells show to some extent the property of irritability—the ability to respond to an external stimulus. The nerve cells, or neurons, are specialized transmitting cells. Each neuron has a body, or soma, with one or more processes. The potential across the membrane when several ions are present on each side in different concentrations is calculated from the Goldman equation. The charge across a cell membrane may be changed by applying a stimulus to the cell. An electrical stimulus is the most obvious way to do this but if the permeability of the cell membrane is changed by chemical or mechanical stimuli, a new local ionic equilibrium will be set up and the potential as a result of ionic concentration differences will change. Because an action potential represents a precise series of membrane permeability changes resulting in predictable membrane potential changes, every action potential in any one axon must be identical. Once the axon has received a supraliminal stimulus, the sequence of membrane permeability and potential changes is set in motion. The larger a nerve fiber the more readily it will conduct impulses.