Medicine

The Inner Ear Anatomy

inner ear

Next to the middle ear in the skull bone is a small compartment containing the hearing and balancing apparatus known as the inner ear. There are two main parts to the inner ear. The cochlea, which is the hearing portion, and the semicircular canals are the balancing portion.

The cochlea is shaped like a snail, and the membrane is divided into two chambers. The chambers are full of fluid that vibrates when the sound comes in and causes the small hairs that line the membrane to vibrate and send electrical impulses to the brain.

Semi-circular canals are also referred to as labyrinthine. These small canals are aligned at right angles (90 °) to each other. This allows the brain to know the direction in which the head is moving. These semi-circular canals are filled with fluid and have some small calcium crystals in the lining.

Coming from the inner ear and running to the brain is the eighth cranial nerve, the auditory nerve. This nerve carries the information of balance and hearing to the brain. The seventh cranial nerve is running along with the eighth cranial nerve. The seventh cranial nerve is also known as the facial nerve because it gives nerve impulses to the muscles of the face.

How does the system work?

The outer ear captures sound waves. The sound goes down the ear canal and struck the ear drum. The ear drum vibrates causing vibration of the ossicles (middle ear bones). An ossicles piston action creates a fluid wave in the inner ear. The fluid wave stimulates the hair cells in the cochlea, and the brain receives an electrical impulse through the eighth cranial nerve.

The system of balance operates by sending continuous electrical impulses to the brain. Moving the head causes the fluid to shift in semi-circular canals. This, in turn, modifies the brain’s electrical impulses. The brain uses this information to make any adjustments for balance which the body needs.

See Also
The Ear Anatomy

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