Formation, Maintenance and Plasticity of Synapses

Abstract

So far, the structure and function of the nervous systems of adult animals has been considered. Furthermore, very little attention has been paid to any dynamic functions over long time scales: neuromodulation and long-term potentiation are the only examples of such functions that have been mentioned. Likewise, no consideration has been given to any structural changes. But the nervous system, like all other systems, develops out of a single cell — the fertilized egg — and the formation of such a complex system that contains so many individual cells whose interconnexions are of paramount importance for its functioning must surely be controlled by a strict set of instructions. Also, during the course of the lifetime of an animal the nervous system may be exposed to numerous threats that might lead to damage (e.g. poisoning, wounds that result in loss of a limb or damage to parts of the central nervous system, infections etc.), and the question arises as to how the nervous system copes with such damage and indeed whether it can cope at all? A related question, even in the absence of externally imposed changes in neuronal structure, is: How are synaptic connexions, once formed during development, maintained during the rest of the animal’s life? Is it necessary for a particular set of synaptic connexions to be used in order for their structural integrity to be maintained? These questions will be considered in this chapter. Finally, a prime function of nervous systems is to learn and to remember, and it would seem that in order to learn and remember there must be changes in the function and perhaps in the structure of synaptic connexions. Chapter 18 will address these problems.