Introduction to Nerve Cells and Nervous Systems

Abstract

The essence of nervous system function is control by means of communication. Unicellular (acellular) organisms, such as amoeba or paramecium, can perform every function necessary to sustain their lives. They can take in nutrients from their external environment, organize their metabolic reactions, excrete waste products into their external environment and move towards or away from entities in their environment, that is, they can perform simple behavioural adjustments to that environment. In multicellullar organisms the constitutent cells have become specialized into organs and tissues for carrying out specific functions, such as digestion and assimilation of foodstuffs, respiration, circulation of the blood to carry oxygen, metabolites and hormones etc. to the tissues, reproduction and so on. The nervous system and the endocrine system together carry out the functions of control and communication, between the various organs and tissues of the body and between the organism and its external environment. In this book we shall consider the structure and function of the nervous system, with special emphasis on vertebrate animals. But invertebrates will be discussed, especially where they illustrate a particularly important principle of neuroscience or where the experimental evidence is compelling. The endocrine system will also be mentioned where appropriate, since there is the closest relationship between nervous and endocrine mechanisms. Some nerve cells function as endocrine cells, and some endocrine cells are modified nerve cells. The main difference in action between nervous and endocrine systems relates to the directness of control.