The Inner Ear
Parts of the Ear: Outer Ear | Middle Ear | Inner Ear
The inner ear contains the sensory organs for hearing and balance. The cochlea is the hearing part of the inner ear. The semicircular canals in the inner ear are part of our balance system.
The cochlea is a bony structure shaped like a snail and filled with two fluids (endolymph and perilymph). The Organ of Corti is the sensory receptor inside the cochlea which holds the hair cells, the nerve receptors for hearing.
The mechanical energy from movement of the middle ear bones pushes in a membrane (the oval window) in the cochlea. This force moves the cochlea's fluids that, in turn, stimulate tiny hair cells. Individual hair cells respond to specific sound frequencies (pitches) so that, depending on the pitch of the sound, only certain hair cells are stimulated.
Signals from these hair cells are changed into nerve impulses. The nerve impulses are sent out to the brain by the cochlear portion of the auditory nerve. The auditory nerve carries impulses from the cochlea to a relay station in the mid-brain, the cochlear nucleus. These nerve impulses are then carried on to other brain pathways that end in the auditory cortex (hearing part) of the brain.
Also housed within the inner ear are the semicircular canals, the utricle, and the saccule. These structures help control one’s sense of steadiness or balance. These balance organs share the temporal bone space with the cochlea. These organs also share the same fluid that is in the cochlea.