Introduction to the central nervous system
Dental students and practitioners need a working knowledge of the central nervous system (CNS) for several reasons.
• A general knowledge of the structure and function of the nervous system is required to understand the major roles it plays in controlling body functions.
• The cranial nerves innervating the head and neck, including the oral cavity, underpin all functions in these areas; knowledge of these nerves, including their connections to the CNS is vital to understanding the anatomy and physiology of this region.
• Clinically, dental students and practitioners will frequently encounter patients suffering from one or other of the many diseases affecting the central and peripheral nervous system. Satisfactory dental management of such patients requires some understanding of their illness which in turn requires knowledge of the general structure of the nervous system.
The anatomy of the nervous system was described long before we understood much of its function. Like all other parts of the body, everything is named; some of the names seem to defy the logic of anatomical nomenclature used to describe structures elsewhere in the body introduced in Chapter 1. Some of the structures visible to the naked eye were named by their fanciful resemblance to everyday objects such as olives; their names, therefore, bear no resemblance to their function. However, the nerve tracts that connect different areas to form functional pathways are described using a consistent system of naming (see Section 3.4.3). Only the most important structures that can be observed in dissected brains or form important landmarks in functional pathways are included in these chapters on the nervous system.
14.2 The study of brain structure and function
It is important to appreciate that much of the detailed structure of the brain can only be observed microscopically. Special microscopical methods are required to show its structure and even then, a practised eye is required to interpret them. Nevertheless, it does help to know the outline of how the connections and functions of the nervous system have been investigated to understand how we have arrived at our present level of knowledge.
14.2.1 Historical methods of investigation
Initially, careful clinical observations of signs and symptoms prior to death were correlated with post-mortem changes in the brain. Diseased parts of the brain revealed at post-mortem implicated that these areas carried out the functions that were observed to be deficient when the subject was still living. Unfortunately, neurological diseases respect neither anatomical nor functional boundaries so many studies, although helpful, were inconclusive. The first designation of function to areas of the cerebral cortex, those involved with language processing, were derived from such methods in the 19th century. In essence, they have stood the test of time but have been significantly modified as new information has become available. Major advances were made from extensive studies of the large numbers of wounded soldiers in the major conflicts of the first half of the twentieth century which were then confirmed and extended by experimental studies.
The next step was to try and repeat clinical findings on experimental animals by artificially injuring key areas and observing the effects. Some advances were made from such experiments. However, they are severely limited in many respects, not the least that it is difficult to investigate higher cognitive functions in animals. In the 1960s and 70s, methods were developed for tracing pathways in the brain. Special dyes that are/>