The Ears and Hearing

Anatomy of the Ear

– external ear• pinna or auricle – outer, funnel-like

structure; collects sound waves traveling through air

• external auditory meatus – tube that leads inward through the temporal bone

• tympanic membrane (eardrum) – cone-shaped membrane attached to the malleus

– reproduces sound waves

Anatomy of the Ear (cont)– middle ear

•tympanic cavity – air-filled space in temporal bone that contains the auditory ossicles

•auditory ossicles: transmit vibrations between eardrum and inner ear

–malleus (hammer) – attaches to the eardrum & vibrates in unison

– Incus (Anvil) – passes the vibration on to the stapes

–stapes (stirrup) – passes vibration onto fluid within the inner ear

Anatomy of the Ear (cont)

– inner ear•semicircular canals – function in equilibrium

•cochlea – contains receptor cells called hair cells; vibrations in the fluid of the cochlea are picked up by the hair cells

– auditory tube (Eustachian tube)•connects middle ear to the throat•conducts air between the tympanic cavity and the outside of the body

•helps maintain equal air pressure on both sides of the eardrum

Popping of Ears •Explain how the auditory tube is related to your ears “popping” when you experience a change in altitude:

– air pressure changes with altitude; so when a person changes altitude, the pressure on the outside of the eardrum changes; this change in air pressure can push the eardrum inward or outward, impairing hearing; when the air pressure difference is great enough, air movement into or out of the auditory tube equalizes the pressure on both sides of the eardrum, and the eardrum moves back to its regular position; this produces a popping sound and restores normal hearing.

– That is why you swallow to equalize the pressure inside and outside the ear drum.

Physiology of Hearing• Steps:

1. Sound waves enter external auditory meatus.2. Eardrum reproduces vibrations from sound wave

source.3. Auditory ossicles (malleus & incus) amplify and

transmit vibrations to end of stapes.4. Movement of stapes transmits vibrations to fluid

of the inner ear.5. Hair cells of inner ear pick up the vibrations in

the fluid.6. The stimulated hair cells release a

neurotransmitter.7. The neurotransmitter stimulates the ends of

nearby neurons which transmit the sensory impulse along the vestibulocochlear nerve to the auditory cortex of the temporal lobe of the brain.

8. The auditory complex interprets the sensory impulse.

Hearing Loss

– conductive deafness – (anatomical deafness) interference with the transmission of vibrations to the inner ear; due to plugging of the external auditory meatus or changes in the eardrum or auditory ossicles

– sensorineural deafness (nerve deafness) – damage to the cochlea, auditory nerve, or auditory nerve pathways; can be caused by loud sounds, tumors in the central nervous system, brain damage, or use of certain drugs