Vestibulocochlear nerve

Last revised by Assoc Prof Frank Gaillard on 25 May 2022

The vestibulocochlear nerve is the eighth (CN VIII) cranial nerve (TA: nervus vestibulocochlearis or nervus cranialis VIII). It exits the brainstem through the cerebellopontine angle, passing into the internal acoustic meatus as part of the acousticofacial bundle. Within the internal acoustic meatus, the nerve branches into cochlear and vestibular nerves to supply the cochlea and vestibule respectively. From these special sensory organs of the inner ear, the vestibulocochlear nerve transmits afferent impulses to the central nervous system encoding auditory stimuli, static (gravitational) equilibrium, and dynamic (rotational) equilibrium.

Vestibulocochlear nerve is the preferred term nowadays but older texts may employ the archaic synonym, acoustic nerve. The Federative Committee on Anatomical Terminology decided decades ago that the nerve's name should more accurately reflect its main functions 6.

The dorsal and ventral cochlear nuclei are located in the dorsolateral upper medulla, deep to the lateral angle of the rhomboid fossa. Situated medial to the cochlear nuclei are the four vestibular nuclei, which form two columns extending rostrally into the lower pons 1,2. Fibers from the vestibular and cochlear nuclei pass around the inferior cerebellar peduncle, exiting the brainstem through the cerebellopontine angle at the pontomedullary junction in the form of distinct vestibular and cochlear roots 2.

In the cerebellopontine angle, the two roots quickly converge to form a single vestibulocochlear nerve. The nerve makes up the most lateral component of the acousticofacial bundle, the other components of which include the facial nerve, nervus intermedius and labyrinthine artery. The vestibulocochlear nerve passes laterally and slightly anterosuperiorly through the cerebellopontine angle cistern, superior to the petro-occipital fissure, inferior petrosal sinus and posterior aspect of the petrous temporal bone 3. It exits the posterior cranial fossa as part of the acousticofacial bundle, passing through the internal acoustic meatus 1,3.

Traveling laterally within the internal acoustic meatus, the vestibulocochlear nerve divides again into vestibular and cochlear roots, which further divide to supply a number of different targets.

The cochlear nerve passes through the anteroinferior quadrant of the fundus (most lateral part) of the internal acoustic meatus. It spirals towards the spiral ganglion located in the modiolus of the cochlea. It is here that first-order neurons projecting from the hair cells of the organ of Corti synapse with second-order neurons of the cochlear nerve 4.

At the fundus of the internal acoustic meatus, the vestibular nerve expands to form the vestibular ganglion, from which the following bundles emerge 2,3:

  • superior division (utriculo-ampullary nerve): courses in the posterosuperior quadrant of the internal acoustic meatus, carrying sensory fibers from the utricle and hair cells of the superior and lateral semicircular canals
  • inferior division (saccular nerve): courses in the posteroinferior quadrant of the internal acoustic meatus to enter the vestibule, carrying sensory fibers from the saccule
  • singular nerve (posterior ampullary nerve): courses in the posteroinferior quadrant of the internal acoustic meatus and through the foramen singulare, carrying sensory fibers from the posterior semicircular canal 5

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Cases and figures

  • Figure 1: upper medulla anatomy - CN VIII (diagram)
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  • Figure 2
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  • Figure 4: brainstem nuclei: dorsal section - Gray's anatomy illustration
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  • Figure 3: Ascending auditory pathway (annotated MRI)
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  • Figure 5: relationship to internal ear
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  • Figure 6: nerves of the internal acoustic meatus (diagram)
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  • Figure 7: cranial nerve origins (illustration)
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  • Case 1 - normal CN VII and VII (T2 MRI)
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  • Figure 8: cranial nerves in the posterior fossa (Gray's illustration)
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  • Case 2: annotated CN VIII and others cranial nerves
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  • Case 3: normal cranial nerves
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