Introduction

Abstract

Living organisms are able to respond to changes in their environment. Large multicellular animals, such as man, achieve this through the activity of a sophisticated arrangement of specialised tissues which allow for rapid and integrated responses to external stimuli. These are the excitable tissues. They include (1) sense organs, (2) peripheral nerves, (3) central nerves and (4) muscles. The sense organs acquire information about the environment; the peripheral nerves communicate it to the central nervous system where it is integrated with data from other sources, and the muscles initiate action based on the processed data.