Anatomy of the inner ear

The inner ear consists of the cochlea and vestibular labyrinth.

The cochlea is a spiral organ of two and a half turns which is divided into three chambers:

• the scala vestibuli
• scala media
• scala tympani

The scala vestibuli and tympani are filled with perilymph and joined at the tip of the cochlea - the helicotrema.

The middle cavity, the scala media, contains endolymph and the organ of Corti. Energy received at the oval window is transmitted to the organ of Corti by vibrations in the endolymph. The hair cells lining the basilar membrane of the organ of Corti then convert this energy into action potentials which pass up the cochlear nerve, eventually to the auditory cortex.

The vestibular labyrinth consists of the utricle, saccule and three semicircular canals arranged at right angles.

The vestibule is concerned with static balance and changes in linear velocity. The role of the semicircular canals is to detect changes in angular velocity. As with the organ of Corti, these structures contain hair cells. In the vestibule, impulses are carried centrally by the vestibular nerve with connections to the cerebellum, spinal cord, and external ocular muscles.