2-3 cm long

terminates in the eardrum or tympanic membrane

has an "S" shape

Separates external and middle ear

Pearly gray in color

Concave with prominent cone of light 5:00 on R; 7:00 on L

Parts of malleus show through: umbo, manubrium and short process

Contains malleus, incus, and stapes

3 Functions:

• conducts sound vibration from outer ear to central hearing apparatus in inner ear
• protects inner ear
• eustachian tube allows equalization of air pressure on each side of the tympanic membrane

bony labyrinth, holds sensory organsfor equilibrium and hearing

vestibular apparatus includesthe vestibule and semicircular canais

Cochlea contains the central hearing apparatus

assess inner ear functions indirectly

sound divided into amplitude (loud) and frequency (pitch) or number of cycles/second

sound waves produce vibrations on tympanic membrane, vibrations carried by middle ear ossicles to oval window, then through cochlea to round window

Normal path of hearing is air conduction (most efficient), alternate route is bone conduction (bones vibrate to transmit sound)

Organ of Corti: sensory organ of hearing

Cranial Nerve VIII: auditory erve sends signals to the brainstem

blocks hearing to external or middle ear

ex. impacted cerumen, foreign bodies, pus in the middle ear, and otosclerosis (decreased mobility of the ossicles)

signifies pathology of inner ear, Cranial nerve VIII or auditory areas of cerebral cortex

irreversible

Fetus: ear develops in 4^th week of gestation. Maternal rubella can damage Organ of Corti and impair hearing

Eustachian tube in child is shorter and straighter - easier to get middle ear infections

Otoscerlosis - common hearing loss age 20-40. Gradual hardening of foot plate of the stapes

Aging Adult: Presbycusis - type of hearing loss with aging or living in noise-polluted area - gradual sensorineural loss. Impacted Cerumen is common; may need irrigation

Otitis Media: more common in N.A., Alaskan and Canadian Inuits, and Hispanics. Also increased in premies, Down Syndrom infants and in babies fed by bottle in supine positions

Cerumen is genetically determined:

Wet: blacks and whites

Dry: Asians and Native Americans