The ear does two jobs: hearing and balance. Both depend on tiny hair cells in the inner ear that turn movement into nerve signals.
Outer and middle ear
Sound waves travel down the ear canal and vibrate the eardrum. Three small bones, the malleus, incus and stapes, amplify the vibration and pass it to the inner ear.
The cochlea
In the fluid-filled cochlea, hair cells bend with the vibration and fire the cochlear nerve. High pitches are sensed near the base of the cochlea and low pitches near its tip.
Balance
The three semicircular canals sense head rotation, and the utricle and saccule sense gravity and straight-line movement. The vestibular nerve sends this to the brainstem and cerebellum, which also use input from the eyes and joints.
Two kinds of hearing loss
Conductive loss comes from a blocked canal, a damaged eardrum or stiff middle ear bones. Sensorineural loss comes from the hair cells or the nerve, as with aging and loud noise.
| Test | Conductive loss | Sensorineural loss |
|---|---|---|
| Rinne (affected ear) | Bone louder than air | Air louder than bone, both reduced |
| Weber | Sound goes to the affected ear | Sound goes to the better ear |
At the bedside
The Weber and Rinne tuning fork tests separate conductive from sensorineural hearing loss at the bedside. Vertigo with nystagmus points to the inner ear or its brainstem connections.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).