Overview
The vestibulocochlear nerve is the 8th cranial nerve, and
gives us afferent information i.e. our balance and hearing. It leaves the skull
through the same opening as the facial nerve (internal acoustic meatus) and arises
from the pontomedullary junction lateral to the facial nerve. The nerve does
not leave the skull, and its to divisions terminate in the inner ear.
Gross Anatomy
The
Vestibulocochlear nerve is also known as cranial nerve 8. It arises from the
pontomedullary junction, lateral to the abducens (which lies just either side
of the midline) and just lateral to the facial nerve. It leaves the cranial
vault through the internal acoustic meatus (an opening in the petrous portion of
the temporal bone), but the nerve never leaves the skull itself. The nerve
divides into the vestibular and cochlear nerve.
The
vestibular division arises from the vestibular system that lies in the inner
ear. The vestibular ganglion is where the bipolar neurons are housed (in the
outer part of the internal acoustic meatus), and it extends processes to five
separate sensory organs. Three if these sensory inputs arise from the ampullae
of the semi-circular canals. The hair cells in the cristae of these ampullae
are displaced in response to rotational acceleration. The maculae of the
saccule and utricle are the other two organs supplies by the vestibulocochlear
nerve. They respond to linear acceleration, which causes the otoliths to be
displaced. The cochlear division begins as the spiral ganglia, which collects
information sent by the inner hair cell displacement in the Organ of Corti.
Clinical Anatomy
Vestibular
schwannoma- This is a tumour of the schwann
(myelin) cells of the vestibular division of the Vestibulocochlear nerve
(cranial nerve 8). Symptoms include dizziness, vertigo, affected hearing (if
the cochlear branch is also impinged), and if the tumour extrudes from the
internal auditory meatus, also impinges the facial nerve, causing a Bell’s
palsy.
Sensorineural
deafness- This is deafness caused by an issue
with the nervous system of the ear itself i.e. he inner ear (cochlear, hair
cells etc). Causes include genetic conditions (Stickler syndrome, Waardenburg
syndrome, Charcot-Marie-Tooth disease), congenital infections (rubella,
cytomegalovirus, toxoplasmosis), Presbyacusis (normal age related hearing
loss), or noise induced hearing loss (from listening to excessively loud music
for a long time.
Labyrinthitis-
Inflammation of the membranous labyrinth damages
the vestibular and cochlear divisions of the vestibulocochlear nerve, resulting
in tinnitus, nausea and vomiting, vertigo and nystagmus. Sensorineuronal
hearing loss also occurs.
Ototoxic
drugs- Ototoxic drugs include Gentamicin (an aminoglycoside
antibiotic), heavy metals such as tin or mercury, as well as carbon monoxide.
Quick Anatomy
Key Facts
Developmental precursor- Metencephalon (secondary brain
vesicle)
Branches- Vestibular nerve, cochlear nerve
Aide-Memoire
Summary
The vestibulocochlear nerve is the 8th cranial nerve, and
gives us afferent information i.e. our balance and hearing. It arises from the
pontomedullary junction lateral to the facial nerve.
References
1.
Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders, Chapter 1 Head
and Neck
2.
Chummy S.Sinnatamby: Last’s Anatomy Regional and
Applied, 12th Edition, Churchill
Livingstone Elsevier
3.
Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier
4.
Elliiot L.Manchell: Gray's
Clinical Neuroanatomy:
The Anatomic Basis for Clinical Neuroscience
5.
The Definitive Neurological Surgery Board
Review
By
Shawn
P. Moore, 2005
6.
Human Neuroanatomy
By
James R. Augustine, 2008