Vestibulocochlear nerve

Nerve: Vestibulocochlear nerve
The course and connections of the facial nerve in the temporal bone
Inferior view of the human brain, with the cranial nerves labelled.
Gray's	subject #203
To	cochlear nerve, vestibular nerve
MeSH	Vestibulocochlear+Nerve

Cranial Nerves
CN I – Olfactory
CN II – Optic
CN III – Oculomotor
CN IV – Trochlear
CN V – Trigeminal
CN VI – Abducens
CN VII – Facial
CN VIII – Vestibulocochlear
CN IX – Glossopharyngeal
CN X – Vagus
CN XI – Spinal Accessory
CN XII – Hypoglossal
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The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain. The acoustic nerve is derived from the embryonic otic placode.

Structure and function

This is the nerve along which the sensory cells (the hair cells) of the inner ear transmit information to the brain. It consists of the cochlear nerve, carrying information about hearing, and the vestibular nerve, carrying information about balance. It emerges from the pons and exits the inner skull via the internal acoustic meatus (or internal auditory meatus) in the temporal bone.

Innervations

The vestibulocochlear nerve consists mostly of bipolar neurons and splits into two large divisions: the cochlear nerve and the vestibular nerve.

The cochlear nerve travels away from the cochlea of the inner ear where it starts as the spiral ganglia. Processes from the organ of Corti conduct afferent transmission to the spiral ganglia. It is the inner hair cells of the organ of Corti that are responsible for activation of afferent receptors in response to pressure waves reaching the basilar membrane through the transduction of sound. The exact mechanism by which sound is transmitted by the neurons of the cochlear nerve is uncertain; the two competing theories are place theory and temporal theory.

The vestibular nerve travels from the vestibular system of the inner ear. The vestibular ganglion houses the cell bodies of the bipolar neurons and extends processes to five sensory organs. Three of these are the cristae located in the ampullae of the semicircular canals. Hair cells of the cristae activate afferent receptors in response to rotational acceleration. The other two sensory organs supplied by the vestibular neurons are the maculae of the saccule and utricle. Hair cells of the maculae activate afferent receptors in response to linear acceleration.

Symptoms of damage

Damage to the vestibulocochlear nerve may cause the following symptoms:

• hearing loss
• vertigo
• false sense of motion
• loss of equilibrium (in dark places)
• nystagmus
• motion sickness
• gaze-evoked tinnitus.^[1]

Name

Some older texts call the nerve the acoustic or auditory nerve [1], but these terms have fallen out of widespread use because they fail to recognize the nerve's role in the vestibular system. Vestibulocochlear nerve is therefore preferred by most.

See also

• Auditory system

References

1. ^ Coad, ML; Lockwood, A; Salvi, R; Burkard, R (2001). "Characteristics of patients with gaze-evoked tinnitus". Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology 22 (5): 650–4. PMID 11568674. 

Additional images

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  Superficial dissection of brain-stem. Ventral view.

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  Dissection showing the projection fibers of the cerebellum.

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  Hind- and mid-brains; postero-lateral view.

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  Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ.

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  Position of the right bony labyrinth of the ear in the skull, viewed from above.

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  Vestibulo-ocular reflex

External links

• MedEd at Loyola GrossAnatomy/h_n/cn/cn1/cn8.htm
• cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University) (VIII)