VIII-Vestibulocochlear
The eighth cranial nerve - the Vestibulocochlear nerve is made up of two parts, the vestibular nerve and the cochlear nerve.
Innervation
- Vestibular apparatus
- Cochlea
Function
Vestibular
- Position and movement of the head
- Posture and balance
Cochlear
- Hearing
Anatomy
The dendrites of both sets of nerves contact hair cells in either the Organ of Corti for the cochlear nerve or the vestibular apparatus for the vestibular nerve. They both pass through the internal auditory meatus and join the brain stem at the cerebellopontine angle which is between the medulla and pons.
Vestibular
The majority of vestibular fibres end in the vestibular nuclei located rostrally in the medulla; there are superior, inferior, medial and lateral vestibular nuclei. From here there is contact with numerous other regions involved in controlling posture, and coordinating head and eye movements. Some fibres enter the medial longitudinal fasciculus which descends as the medial vestibulospinal tract which can influence the spinal motor neurones, therefore controlling posture and balance. The ascending component of the medial longitudinal fasciculus goes on to connect with other nuclei in the brain stem involved in coordination of head and eye movements. There are also connections with the cerebral cortex involved in the conscious awareness of vestibular sensation.
Click here for a diagram showing the central connections of the vestibular nerve
Cochlear
The fibres from the cochlear nerve end in the cochlear nuclei where the ascending auditory pathway then starts, this is complicated and there are lots of regions where axons synapse and not all fibres behave in the same way. Some fibres decussate whereas others do not giving a bilateral representation of the cochlea in the primary auditory cortex. The infomation is interpreted in the auditory association cortex (Wernicke's area) and is important in the processing of language.
Click here for a diagram of the central connections of the cochlear nerve