Inner Ear and Hearing

The anatomy of the inner ear can be a little confusing because two systems come together in this part of the anatomy adding balance to the hearing function. The inner ear looks from the side like a snail, where the body or shell of the snail represents the organ of hearing, the cochlea and the “head and neck” of the snail is the organ of balance and equilibirium, the vestibular system. 

inner-ear-3dBoth of these systems compose the bony labyrinth containing tubes filled with fluid encased within the temporal bone of the skull. The bony tubes also contain a set of cell membrane lined tubes within which the cells that are responsible for hearing call inner hair cells because of the hairs that appear on their surface as seen under the electron microscope. 

hair-cellsThe bony labyrinth contains three sections. The first, is the cochlea, the hearing organ, then the semicircular canals that jutt out in all three directions in space (X, Y and Z). The semicircular canals provide out brain with tinformation about any circular or rotational movement or acceleration such as the one that happens when you turn around in a circle or roll down on a grassy hill or experience when performing a summersault.

vestibular-systemFinally, the area between the semicircular canals and the cochlea (the neck of the snail) is the vestibule which contains two smaller structures within it the saccule and the utricle. This area is responsible for our brain’s sensation of acceleration in a straight line either forward or backward and upward and downward.

We hear by funneling sound from the environment into the outer ear and causing the eardrum, or tympanic membrane to vibrate. Those sound waves vibrations are transferred into mechanical vibrations of the little bones in the ear called the ossicles. Those mechanical vibrations cause the oval window which is the separation between the middle and inner ear to move back and forth causing the fluid within the inner ear  to begin a wave-like motion. The  wave motion is felt more strongly along different lengths of the cochlea based on the pitch of the sound and is transformed into electrical impulses picked up by the inner ear hair cells. These electrical signals are then sent to the brain via the hearing or cochlear nerve for final processing.