Twelve pairs of special nerves called cranial nerves (CNs) emerge from the cranial vault through skull foramina and canals to structures in the head and neck. They are numbered sequentially with Roman numerals in rostral to caudal order as they arise from the brain. CNs III through XII arise from the diencephalon and the brainstem, as illustrated in Figure 1. CNs I and II are actually fiber tracts emerging from the brain. Some CNs are limited to general motor and/or sensory functions, whereas others are specialized, serving smell, vision, or hearing (I, II, VIII).

Functions of the CNs most relevant to the physical examination are summarized on the next page.

FIGURE 1. Brain anatomy—inferior surface.

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