As the name implies, the vestibulocochlear nerve (or cranial nerve VIII), consists of two distinct parts: the vestibular nerve and the acoustic nerve. Although they both carry afferent information from the inner ear to the brain, the type of information they carry is different. The vestibular nerve carries information from your ear to your brain about balance and equilibrium and the acoustic nerve carries information to your brain about hearing. Cranial nerve VIII is responsible for sound sensitivity and controlling sensitivity to dynamic changes in equilibrium.
A lesion on the vestibular nerve would result in nystagmus (rhythmic oscillations of the pupil), unsteady gait, nausea and vertigo. A lesion on the auditory nerve would result in hearing loss and/or tinnitus. One of the most common brain tumors, a vestibular schwannoma or acoustic neuroma, occurs on the vestibular portion of cranial nerve VIII and is marked by the many of the above mentioned signs and symptoms. Many patients complain on tinnitus in one ear with fullness in that ear. Although acoustic neuromas are typically slow growing and benign, in rare cases they may grow large enough to compress the brainstem and threaten the patient’s life.
How it relates to speech-language pathology: Knowledge about cranial nerve VIII is important for speech-language pathologists because an intact auditory nerve is essential to receive auditory information including speech and language. Not only is access to speech and language important for daily function, but it is also critical that the patient has access to sound for speech therapy to have the maximum benefit. It would be negligent for a speech pathologist to start speech and/or language therapy without first verifying that the patient’s auditory system is intact. Speech pathologists typically do this through a hearing screening. If a speech-language client reports dizziness, vertigo, or tinnitus they should be referred to a neurologist or otolaryngologist for fuller testing.