Functional Systems

The preceding chapters presented the major structures seen at individual levels of the central nervous system (CNS) or in particular views of the brain. This chapter is complementary, using many of the same sections and views to indicate the structures and connections involved in particular neurological functions.

We have taken a “bare-bones” approach to this task and indicated only major pathways and connections. Much of the circuitry discussed in standard textbooks has been omitted in the interest of simplicity. The locations of neuronal cell bodies, the trajectories of their axons in tracts, and the locations of their synaptic endings are usually indicated by cartoon neurons like this one:

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In addition, some anatomical liberties were taken to keep the diagrams relatively simple. The number of lines was minimized by indicating axons as diverging or converging:

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(Axons frequently branch to innervate multiple targets, but this is not what we mean to indicate in any of these figures; moreover, axons from multiple neurons never converge to form a single axon.)

Finally, colors were used to make it easier to follow particular pathways in each figure. Their use is consistent within a given figure but not across figures: We were unable to devise a meaningful color scheme that would accommodate all the different functional systems. Hence a given color seldom has a functional implication.