CN VIII. Vestibulocochlear Nerve
The vestibulocochlear nerve is a sensory nerve that conducts two special senses: hearing (audition) and balance (vestibular). The receptor cells for these special senses are located in the membranous labyrinth which is embedded in the petrous part of the temporal bone. There are two specialized organs in the bony labyrinth, the cochlea and the vestibular apparatus. The cochlear duct is the organ that is connected to the three bony ossicles which transduce sound waves into fluid movement in the cochlea. This ultimately causes movement of hair cells which activate the auditory part of the vestibulocochlear nerve. The vestibular apparatus is the organ that senses head position changes relative to gravity. Movement causes fluid vibration resulting in hair cell displacement that activates the vestibular part of the eighth nerve. The peripheral parts of the eighth nerve travel a short distance to nerve cell bodies at the base of the corresponding sense organs. From these peripheral sensory nerve cells the central part of the nerve then travels through the internal auditory meatus with the facial nerve. The eighth nerve enters the brain stem at the junction of the pons and medulla lateral to the facial nerve. The auditory component of the eighth nerve terminates in a sensory nucleus called the cochlear nucleus which is located at the junction of the pons and medulla. The vestibular part of the eight nerve ends in the vestibular nuclear complex located in the floor of the fourth ventricle.