The biological study of animal behaviour was put on a sound footing by the early ethologists in the middle of the twentieth century. These etholo-gists pioneered techniques for investigating the natural behaviour of animals, including the use of simple experiments in conjunction with field observations. In the course of this work, they developed a number of key concepts that have helped to guide efforts to understand the mechanisms of behaviour.
One such concept is that of the motor pattern, which is a relatively stereotyped sequence of movements and is easily recognised as part of an animal's ongoing behaviour. The recognition of these motor patterns in the animal's natural behaviour clearly implies that there is a corresponding pattern in the underlying organisation of the animal's nervous system, which generates these movements. Another concept is that of the releasing mechanism, which may be envisaged as a kind of neural filter tuned to recognise specific sign stimuli in the environment. The nervous system must be organised so as to sort out different stimuli and to make decisions about which motor pattern to put into action at any one time. The egg retrieval response in nesting birds provides a good example of the development of these two concepts.
The way that particular nerve cells can be identified as playing specific roles in the control of behaviour is well illustrated by the T5(2) neurons in the brains of toads. The close correspondence between the responses of these neurons and the sign stimuli for prey catching in the toad (Bufo) suggests that these cells are part of the natural releasing mechanism for prey-catching behaviour. This conclusion is backed up by lesion experiments, which alter the responses of these nerve cells and the behaviour of the intact animal in similar ways.
Much recent research in neuroethology is aimed at understanding how nerve cells are organised into circuits that perform specific functions in behaviour, such as filtering out sign stimuli or generating a particular motor pattern. This work involves tracing the flow of signals from one nerve cell to the next, and is most easily done where particular nerve cells can be uniquely identified. An essential first step along this path to understanding how nervous systems underlie behaviour is to examine the relevant properties of the fundamental units of the nervous system, the nerve cells.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.