Functional classification of cranial nerve nuclei
A nucleus is a collection of neurons, with similar function, that are clustered together and located in the CNS. Cranial nerve nuclei can have two different names depending on whether their function is somatic or autonomic (parasympathetic).
For example, the oculomotor nucleus of CN III supplies some of the extraocular muscles, while the parasympathetic nucleus of CN III innervates smooth muscle of the eye and orbit. Some nuclei contain neurons of multiple cranial nerves yet all those neurons have a similar function. For example, the nucleus ambiguus, comprising neurons associated with CN IX, X and XI, innervates the striated muscle of the larynx and pharynx.Cranial nerves may have one type of function only, or have several functions. It should be noted that even the ‘motor only’ nerves may contain proprioceptive afferent fibres. Motor fibres of cranial nerves form the lower motor neurons (LMNs) of the head region (Table 10.3). Note that CN VIII has traditionally been described as purely sensory, however efferent fibres have been described in both the vestibular and cochlear portions of CN VIII (Chapter 10, olivocochlear reflex).
Table 10.3 General functions of cranial nerves
| Sensory only | I, II, |
| Motor only | III, IV, VI, XI, XII |
| Mixed sensory and motor | V, VII, VIII*, IX, X, |
| Autonomic (parasympathetic) | III, VII, IX, X |
* efferent components have been described in CN VIII
Rather than considering the 12 cranial nerves in isolation, it is useful to group them by function.