Cranial nerve nucleus

A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei excepting that of the IV nerve supply nerves of the same side of the body.

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Arrangement of the nuclei

Just as grey matter in the ventral (closer to front of a human) spinal cord tends to be efferent (motor) fibers, and the dorsal horn tends to contain sensory neurons, nuclei in the brainstem are arranged in an analogous way.

• Close to the midline are the motor efferent nuclei, such as the oculomotor nucleus, which control skeletal muscle. Just lateral to this are the autonomic (or visceral) afferent nuclei.

• There is a separation, called the sulcus limitans, and lateral to this are the sensory nuclei. Near the sulcus limitans are the visceral afferent nuclei, namely the solitary tract nucleus.

• More lateral, but also less posterior, are the general somatic afferent nuclei. This is the trigeminal nucleus. Back at the dorsal surface of the brainstem, and more lateral are the special somatic afferents, this handles sensation such as balance.

• Another area, not on the dorsum of the brainstem, is where the branchial efferent nuclei reside. These formed from the branchial arches, in the embryo. This area is a bit below the autonomic motor nuclei, and includes the nucleus ambiguus, facial nerve nucleus, as well as the motor part of the trigeminal nerve nucleus.

Examples of nuclei

There are several cranial nerve nuclei (roman numeral refers to the cranial nerve number):

hindbrain (rhombencephalon)

medulla oblongata

• Hypoglossal nucleus (XII) - motor
• Dorsal motor nucleus of vagus nerve (X) - visceromotor
• Nucleus ambiguus (IX, X, XI) - motor
• Solitary nucleus (VII, IX, X) - sensory
• Spinal trigeminal nucleus (V) - sensory
• Inferior olivary nucleus afferent fibres to cerebellum

pons

• Cochlear nuclei (VIII) - sensory
  • Dorsal cochlear nucleus
  • Ventral cochlear nucleus
• Vestibular nuclei (VIII) - sensory
• Salivary nuclei - visceromotor
  • Inferior salivary nucleus (IX)
  • Superior salivary nucleus (VII)
• Facial nucleus (VII) - motor
• Abducens nucleus (VI) - motor
• Trigeminal motor nucleus (V) - motor
• Spinal trigeminal nucleus (V) - sensory

midbrain (mesencephalon)

• Mesencephalic trigeminal nucleus (V) - sensory
• Red nucleus - motor, extrapyramidal
• Trochlear nucleus (IV) - motor
• Oculomotor nucleus (III) - motor
• Edinger-Westphal nucleus (III) - visceromotor

References

• Lennart Heimer, The Human Brain, ISBN 0-387-94227-0

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