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Biology 14 Human ears Cheat Sheet by

Growth and development


3 regions

How we hear

Sound waves
collected by pinna are directed to eardrum
causes eardrum to vibrate
amplify and transmit vibration to oval window
Oval window
cause perilymph in cochlea to vibrate
vibrations in perilymph is transm­itted to endolymph of cochlea
Sensory hair cells (central canal)
generate nerve impulses
produce sensation of hearing
nerve impulses travel along auditory nerves to auditory centre in brain
vibration in perilymph transm­itted to round window
Round window
releases fluid pressure in the cochlea to the air in middle ear

Outer ear

Pinna (ear flap)
flap of cartilage covered by skin
collects sound waves in surrou­nding
directs them along auditory canal to eardrum
Auditory canal
produces wax
lubricates canal
traps dirt and bacteria to prevent them entering the middle ear
thin, elastic membrane at the end of auditory canal
convert sound waves to vibrations

Middle ear

Ear bones
3 tiny ear bones
smallest bones in body
amplify and transmits vibration from eardrum to oval window
Oval window
flexible membrane
transmits vibration from ear bones to inner ear
Round window
releases fluid pressure in cochlea into the air
Eustachian tube
tube connecting middle ear to pharynx
normally closed
swallowing to open it to allow air to enter or leave middle ear
equalised the pressure on either side of eardrum
Unequal pressure
eardrum will bulge
bulging eardrum cannot vibrate freely
cannot hear clearly

Inner ear

for hearing
coiled tube with three parallel canals separated by membranes
fluid in upper and lower canal
fluid in central canal
sensory hair cells
in central canal
detects vibrations of endolymph
endolymph vibrates
sensory hair cell hairs are bent
sensory hair cells generate nerve impulses
nerve impulses travels along auditory nerves to auditory centre in brain
Semici­rcular canals
not involved in hearing
sensory hair cells
detection of head movements
stimul­ated, send nerve impulse to brain
brain coordinate muscled to maintain body balance


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