The cranial nerves

Abstract

The cranial nerves are the most important neural structures relevant to dental students and practitioners. The cranial nerves are the nerve supply to all the structures in the head and neck and underpin of the anatomy and function of these regions—the head and neck will not work without them. In a wider context, correct functioning of the cranial nerves is a very good indicator of the health or otherwise of the CNS; it may be necessary to test the function of some, or even all, of the cranial nerves at times to assess neural function. In addition, many of the cranial nerves may be involved in various diseases of the head and neck. As outlined in Chapter 3, 12 pairs of cranial nerves arising from the brain form one major component of the peripheral nervous system, the 31 pairs of spinal nerves forming the other. Each pair of cranial nerves has a name and number. Conventionally, they are numbered using the Roman numerals I to XII. The nerves are numbered from one to 12, according to their origin from the brain; nerves with the lowest numbers arise from the most anterior aspect of the brain (the forebrain) whereas those with highest numbers arise from the lowest part (the medulla). Several aspects of any nerve anywhere in the body are required to d escribe its anatomy and function in complete detail: • Its origins and terminations in the CNS; • Its neuronal components—are they motor, sensory, or autonomic? • Its course to and from its target tissues; • Its distribution to specific areas and structures through specific branches; • Its overall functions and specific functions of its component parts. In addition, if the clinical significance is going to be appreciated, we w ill also need to consider: • The effects of damage or disease on the nerve; • Its important relationships to other structures; • How to test whether the nerve is functioning correctly. Given that there are 12 pairs of nerves, does a competent dentist need to know everything in the two lists about every cranial nerve? The answer, you will be relieved to hear, is ‘no’.