Ear

The structures of the ear support the functions of hearing and balance. The ear has three divisions:

• The outer ear consists of the auricle (pinna) and auditory canal, structures that collect, focus, and channel sound waves.
• The middle ear consists of the auditory ossicles, three tiny bones that vibrate in sequence to focus and amplify sound.
• The inner ear contains the COCHLEA, which converts sound waves to NERVE impulses, and the structures of the vestibular system that regulate balance, the bony labyrinth, and the semicircular canals.

The TYMPANIC MEMBRANE, or eardrum, separates the outer ear and the middle ear; the EUSTACHIAN TUBE connects the middle ear with the THROAT to equalize pressure on both sides of the eardrum. Many causes of HEARING LOSS arise as a result of damage to or dysfunction of the structures of the outer and middle ear. The inner ear is entirely sealed from the external environment. Fluid bathes the delicate structures of the inner ear, helping protect them as well as isolate them from external stimuli that could affect their functions. Most disturbances of balance, often called vestibular dysfunction, stem from problems with the inner ear.

COMMON CONDITIONS AFFECTING THE EAR, HEARING, AND BALANCE

• ACOUSTIC NEUROMA BAROTRAUMA
• CHOLESTEATOMA HEARING LOSS
• LABYRINTHITIS MÉNIÈRE’S DISEASE
• MYRINGITIS OTITIS (INFECTION)
• OTOSCLEROSIS OTOTOXICITY
• TINNITIS VERTIGO