Transcript The Ears and Hearing

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) – coneshaped 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