Download THE EAR: Hearing and Balance

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Chapter 10
1. Outer (external)
2. Middle
3. Inner (internal)
balance & hearing
Auricle (pinnae)
External auditory meatus (auditory canal)
Tympanic membrane
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Oval Window
Cochlea (*Organ of Corti)
Cochlear nerve
Sound waves enter the external auditory
Waves of changing pressure cause the eardrum
to reproduce vibrations coming from sound a
wave source.
Auditory ossicles amplify and transmit
vibrations to end of stapes.
Movement of stapes at oval window transmits
vibrations to perilymph of cochlear duct.
Vibrations pass through the vestibular
membrane and enter endolymph of cochlear
6. Different frequencies of vibration in endolymp
stimulate different sets of receptor cells.
7. As a receptor cell depolarizes, its membrane
becomes more permeable to calcium ions.
8. Inward diffusion of calcium ions causes vesicles at the
base of the receptor cell to release
9. Neurotransmitter stimulates ends of nearby sensory
10. Sensory impulses are triggered on fibers of the
cochlear branch of vestibulocochlear nerve.
11. Auditory cortex of the temporal lobe interprets
sensory impulses.
 Decibels (dB): measure sound intensity
Whisper 40dB
Rock concert 120dB
Normal conversation 60-70dB Jet plane 140dB
 Frequent or prolonged exposure to sounds above 85dB
can damage hearing receptors and cause permanent
hearing loss.
 Frequency: number of vibrations or sound waves per
 Human: can detect sounds with a frequency of 20-
20,000 per minute
 Dog: 60-45,000
 Rat: 650-60,000
 Bat: 3,000-120,000
 Static equilibrium: sense of position of the head,
maintaining stability and posture when the head and
body are still. (vestibule)
 Dynamic equilibrium: detect head and body motion
and aid in maintain balance (semicircular canals)
 All of this information goes to the cerebellum
 Ear-popping: aids in equalizing pressure
 Your auditory tube is normally flattened and closed, but
swallowing or yawning can open it to equalize pressure
between the middle ear cavities with the atmospheric
pressure. The eardrum will not vibrate unless pressure
is equal. If there is unequal pressure, the eardrum
bulges causing hearing difficulties and earaches.
 Otitis media: inflammation of the middle ear. Can
be caused by sore throats in children.
 Myringotomy: implanting of a tiny tube to drain fluid
& pus accumulation
 *Children have a more horizontal auditory tube*
 2 types
 Conduction: temporary or permanent; results when
something interferes with the conduction of sound
vibrations to the fluid of the inner ear.
Wax build-up
Otosclerosis (fusion of the ossicles)
Ruptured eardrum
Otitis media
Hearing aids: use skull bones to conduct sound vibrations to
inner ear.
 Sensorineural: degeneration or damage to the receptor
cells in Organ of Corti, cochlear nerve, or to neurons of
the auditory cortex. Results from a problem of nervous
system structures or by extended listening to excessively
loud sounds.
 Hearing aids are less helpful
 Meniere’s disease: a pathological condition of the
inner ear characterized by vertigo (sensation of
spinning), tinnitus (ringing in the ears), and
progressive loss of hearing.
 Presbycusis: occurs because of changes in the inner
ear. Very common in older people.
 Otosclerosis: spongy bone formation that causes
deafness by fixing the stapes to the oval window.