Sensory System
Ear: Sound & Balance
3 Parts: Outer –
Middle - Inner
Outer Ear: Auricle
• Called the Pinna
– Fx: Collects sound
waves
–Visible part of the
ear, outside the
head
Outer Ear: External
Auditory Canal
• Extends
from Pinna
to eardrum
– Fx:
Transmits
sound waves
Outer Ear: External
Auditory Canal
• Produces
Cerumen
(earwax)
–Fx: Traps
foreign
bodies
Middle Ear:
• Air-filled
• Converts sound waves
to mechanical energy
• Amplifies it
• Conducts to next
chamber
Components:
• Tympanic membrane –
Eardrum
– Vibrates
– Sound to
Mechanical
Energy
Perforated Eardrum:
Otitis Media
• Inflammation of the
middle ear
Components:
• Ossicles – 3 bones
– Malleus (Hammer)
– Incus (Anvil)
– Stapes (Stirrup)
• Fx: Mechanical
vibration
Middle Ear: Ossicles
•
Ear Ossicles
Middle Ear:
• Oval window - Tranfers
mechanical vibration
from middle ear to
inner ear
View of
OVAL WINDOW
Oval
Window
Middle Ear opens to
Nasopharynx via
Eustachian tube
Eustachian Tube
Fx:
• Adjusts pressures between middle
ear & outside
• Drains middle ear
Eustachian Canal
• Normally closed
• Swallowing & yawning open it
• Tympanic membrane will not
vibrate well if pressures not
equal
Eustachian Canal
• If fail to open, increased
pressure (pain) and infections
Requires Ear Tubes – drain the
excess fluid & prevent infection
Inner
Ear
• Bony Chambers (fluid-filled)
• Vestibule
• Semicircular Canals
• Cochlea
Inner Ear Bony
Labyrinth
Inner Ear Bony
Labyrinth
• Fluid-filled = Perilymph
• Membranous sac is
suspended in the
periliymph =
Membranous labyrinth
Inner Ear Membranous
Labyrinth
• Sac contains thick fluid
= Endolymph
Hearing and
the Inner
Ear Cochlea
• Snail-like shape
• Membranous sac
contains organ of Corti
Cochlear Ducts
Perilymph
Membranous
labyrinth
Endolymph
Organ of Corti
Organ of Corti
• Contains specialized
hearing receptors or
hair cells
• Embedded in basilar
membrane
Organ of Corti
• Hair cells covered by
gel membrane (Tectorial
membrane)
• Corti converts
mechanical energy into
electrochemical energy
Hearing Process
• Ossicles vibrate oval
window
• Sets the fluids into
motion (pressure waves)
Hearing Process
• Vibrate basilar
membrane
• Hair cells rub tectorial
membrane (bent)
Hearing Process
• Hair cells transmit
impulse to cochlear
nerve
• Interpretation of sound
in temporal lobe
Sound Energy to Hearing
Interpretation
Mechanical Mechanical 
Sound Energy
Energy Electrochemical
Balance:
Static Equilibrium
• Position of head when
not moving (which way
is up)
• Membranous sacs in
vestibule contain
maculae
Maculae
Physiology
• As head moves,
otoliths roll in
response to
gravity
• Pulls on gel and
bends hairs in
receptors
Maculae Physiology
• Hair cells send impulse
via vestibular nerve
• Signal to cerebellum for
interpretation
Balance:
Dynamic Equilibrium
• Rotation of head or
movement is detected
• Membranous
semicircular canals
filled with endolymph
Crista Ampullaris
• Membranous
semicircular canals
contain crista
ampullaris
Crista Ampullaris
• Contains receptor cells
(w/ hairs) embedded in
cupula (gel-like cap)
Ampullaris Physiology
• When head
moves,
endolymph lags
behind
• Cupula drags
against
endolymph
current and
bends hairs
Ampullaris Physiology
• Stimulates hair cells to
send impulse
• Vestibular nerve sends
impulse to cerebellum