Cranial nerve nuclei

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The cranial nerve nuclei are collections of neuronal cell bodies dispersed throughout the brainstem. They function to either receive afferent inputs from cranial nerve fibers or give off efferent outputs which travel along the cranial nerves to target structures. 

The cranial nerve nuclei can be divided into seven different modalities based on the information they carry to and from their target tissues, impulse type and specificity or exclusivity to cranial nerves: 

Efferent modalities 

• General somatic efferent (GSE): skeletal muscles of the head and neck (e.g. extraocular muscles and muscles of the tongue).

• General visceral efferent (GVE): smooth muscles of gut and autonomic motor (e.g. smooth muscles of the salivary glands and iris sphincter muscle and the ciliary muscle.

• Special visceral efferent (SVE): muscles derived from pharyngeal arches, specific to cranial nerves.

Afferent modalities

• General somatic afferent (GSA): general sensation from the skin.

• General visceral afferent (GVA): general sensation from viscera.

• Special somatic afferent (SSA): senses derived from ectoderm, specific to cranial nerves (e.g. sight, sound, balance).

• Special visceral afferent (SVA): senses derived from endoderm, specific to cranial nerves (e.g. taste, smell).

It is important to note that while cranial nerves can carry a mixture of both motor and sensory fibers, cranial nerve nuclei can only be motor or sensory. Therefore, cranial nerves may be associated with more than one nucleus and some cranial nerves may even share the same nucleus. 

The olfactory nerve (CN I) and the optic nerve (CN II) arise outside the brainstem and therefore, are the only cranial nerves which are not associated with cranial nerve nuclei. 

Find out more about the afferent and efferent cranial nerve nuclei by watching the video below.

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Summary