MODULE 8
THE CONCEPT of FUNCTIONAL COMPONENTS
- - - Most of you will be familiar with the concept of functional components from Gross Anatomy. Our version of the concept is shown in Figure 8-3. Unlike most authors we think the notion of a special somatic afferent column is pointless, so we omit it. Figure 8-4 shows the cell columns on a section through the medulla and introduces the color code we will use in subsequent brainstem sections.
- - - All textbooks include a dorsal view of the brainstem in which the position of the cell columns representing each functional component is shown. We give you a number of views of this sort:
- - - While we generally avoid dealing with the peripheral nervous system, leaving this for the gross anatomists, it is difficult to do so in the case of the cranial nerves. For example, you can't really understand how to test the accessory nerve unless you are familiar with the actions of the muscles it innervates. So, in doing this module we suggest you refer frequently to Chapter 9 in Clinically Oriented Anatomy, Fourth Edition by Keith L. Moore and Arthur F. Dalley. The figure on their page 1084 (part of Table 9.1) is a painless summary of the cranial nerves and we will use the table on page 1085 as the final authority in ruling on cranial nerve disputes. We say this to alert you to the fact that such disputes do exist and that it is probably a mistake to spend too much time figuring out who is right. To give just one example Blumenfeld stresses that the accessory nerve innervates only the upper part of the trapezius muscle, while Moore says it innervates the entire muscle. In this case, Kandel agrees with Moore. We really don't know what the evidence is, but we're going to go with Moore when differences of this sort arise.
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