Download The Special Senses

Still Chapter 17
Hearing & Balance
HEARING
3 main parts of
the ear:
• Outer Ear
• Middle Ear
• Inner Ear
Outer Ear
• Pinna = outside portion
of the ear, focuses
sound waves on the
eardrum (tympanic
membrane)
• External auditory
canal = ear canal, leads
to the eardrum, contains
ceruminous glands that
secrete earwax
• The eardrum separates the outer and middle
ear
Middle Ear
• Sound vibrations from the
eardrum pass to auditory
ossicles (three tiny bones –
malleus/hammer,
incus/anvil, &
stapes/stirrup) which
transmit sound to the inner
ear
• Eustachian tube connects
to pharynx, allowing air
pressure to equalize on both
side of the eardrum; can be
blocked by infections
The Inner Ear
• Cochlea filled with
fluid picks up vibrations
from middle ear which
cause hair cells in
cochlea to bend
• Movement of hair
converts vibrational
energy into nerve
impulses
Auditory Pathway
Vestibulocochlear
nerve VIII takes
the information to
medulla oblongata
and then to
auditory cortex in
the temporal lobe
Sound Levels of Common Noises
Safe
range
Risk
range
Injury
range
Sound
Intensity
Noise Source
60 db
Normal conversation, bird song
80 db
Heavy traffic, ringing phone
85 – 90 db
Motorcycle, snowmobile
90 db
Hair dryer, lawn mower
95 – 105 db
Hand drill, bulldozer, spray painter
110 db
Chain saw
120 db
Ambulance siren, rock concert
140 db
Jet engine at takeoff
165 db
Shotgun blast
BALANCE & COORDINATION
• Maintain balance
and equilibrium
• Filled with fluid
and hair cells
• When you tilt your
head, fluid and hair
move and stimulate
nerve cells to carry
info to cerebellum
Semicircular Canal in
Inner Ear