Ear: Anatomy of Hearing and Balance (cont.)

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The inner has two functions; the first is hearing and the second is balance. It is a warren of tubes filled with fluid encased within the temporal bone of the skull. The bony tubes also contain a set of cell membrane lined tubes. The bony tubes are called the bony labyrinth filled with perilymph fluid, which the membranous labyrinth tubes are filed with endolymph. This is where the cells responsible for hearing are located (the hairy cells of Corti).

The bony labyrinth itself has three sections. 1) The cochlea is responsible for hearing, 2) the semicircular canals have function associated with balance, and 3) the vestibule which connects the two and contains two more balance and equilibrium related structures, the saccule and utricle.

The final structures of the inner ear are the round window and the eighth cranial nerve (cranial nerve VIII) which is composed of the vestibular nerve (balance) and the cochlear (hearing) nerve.

Picture of the Anatomy and Structures of the Ear
Diagram of outer, middle, and inner ear. The outer ear is labeled in the figure and includes the ear canal. The middle ear includes the eardrum (tympanic membrane) and three tiny bones for hearing. The bones are called the hammer (malleus), anvil (incus), and stirrup (stapes) to reflect their shapes. The middle ear connects to the back of the throat by the Eustachian tube. The inner ear (labyrinth) contains the semicircular canals and vestibule for balance, and the cochlea for hearing.


We hear by funneling sound from the environment into the outer ear and causing the tympanic membrane to vibrate. Those sound waves vibrations are transferred into mechanical vibrations of the ossicles. Those mechanical vibrations cause the oval window to move back and forth causing the perilymph of the inner ear to begin wave-like motions. The perilymph fluid motion is transferred to the endolymph and the wave motion is transformed into electrical impulses picked up by the hairy cells of Corti and sent to the brain via the cochlear nerve. The round window is responsible for absorbing the fluid wave vibrations and releasing any increased pressure in the inner ear caused by the wave motion.


Balance is a choreographed arrangement that takes sensory information from a variety of organs and integrates it to tell the body where it is in related to gravity and the earth.

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