Though everyday movements like blinking or scratching an itch can seem simply executed, each is dependent on the transmission of messages between the brain and the rest of the body. Hearing is one such experience. It is dependent on the eighth cranial nerve, called the vestibulocochlear or auditory nerve, which also has a branch that controls balance. Any disruptions to the nerve pathway can have major impacts on one's senses of hearing and balance.
The Ear, Inside and Out
The
ear has an outer, middle and inner part. The outer ear conducts sound waves through the ear canal to the eardrum. The eardrum vibrates and moves the three bones of the middle ear: malleus, incus and stapes. The stapes is connected to a network of liquid-filled tubes, or canals. Motion of the liquid inside these canals allows electric signals to be sent via the auditory nerve to the brain. Any problems with the auditory nerve result from problems in the inner ear, the auditory nerve itself, or the part of the brain it connects to.
Labyrinthitis is one of them. This viral or bacterial infection will inflame the inner
ear, also known as the labyrinth, and prevent sensory information from traveling along the auditory nerve. Bacterial labyrinthitis may be caused by chronic, untreated ear infections, and viral labyrinthitis may be connected to viruses such as herpes, influenza, measles, mumps and polio – so it’s important to stay on top of your doctor’s appointments and vaccinations.
The Ear and the Brain: Too Close for Conduction
This 46-year-old man would agree. He came to a neurosurgery clinic with complaints of worsening tinnitus and vertigo that eventually made it extremely difficult for him to work or carry out daily activities.
Exploratory surgery unearthed the cause: a large vein pressing on the auditory nerve by looping around it. Once the vein was removed from the nerve, his symptoms disappeared. This was a case of
microvascular compression syndrome (MCS), which is rare but can be debilitating.
The Ear and the Brain: A Play on Words
Ever hear the expression, “That went right over my head?” Someone with auditory cortex damage might mean it literally. The
auditory cortex is located in the temporal lobe of the brain, and therefore helps us hear spoken words in their proper order. If that area is damaged, you may still hear words, but you wont be able to understand them correctly. The same would apply to other forms of sound that require temporal processing, such as music.
Test it Out: Ear or Brain?
Several tests exist to assess your auditory nerve transmission, such as
auditory brain-stem response (ABR) testing and
electrocochleography (ECoG). Consult your local audiologist if you’ve noticed changes in balance and hearing – there might be something getting on your nerves.
by Estie Neff
