11. The Ear

Contains receptors for hearing and balance, in three regions:

• Outer ear: pinna, auditory meatus, and the eardrum (tympanic membrane).
• Middle ear: air-filled; contains the malleus, incus and stapes (ossicles) and the Eustachian tube (pressure balance).
• Inner ear: fluid-filled; contains the cochlea (hearing — organ of Corti) and the semicircular canals + utricle/saccule (balance).

Hearing Pathway

Sound waves → pinna → auditory canal → eardrum vibrates → ossicles amplify vibration → oval window → fluid in cochlea moves → hair cells of organ of Corti stimulated → impulse via auditory nerve → brain.

Balance

Head movement disturbs fluid in the semicircular canals, bending sensory hairs and generating impulses to the cerebellum; the utricle/saccule use otoliths to detect static position and linear movement.