6. Tympanic Membrane
• Cone-shaped in appearance
• The eardrum separates the outer
ear from the middle ear
• Creates a barrier that protects the
middle and inner areas from
foreign objects
• The eardrum vibrates in response
to sound pressure waves.
• The membrane movement is
incredibly small as little as one-
billionth of a centimeter
7. Function of Outer Ear
• Collect sound
• Localization
• Resonator
• Protection
• Sensitive (earlobe)
8. Cerumen/ Earwax
The purpose of wax:
• Repel water
• Trap dust, sand particles, micro-
organisms, and other debris
• Moisturize epithelium in ear
canal
• Odor discourages insects
• Antibiotic, antiviral, antifungal
properties
• Cleanse ear canal
12. Function of Middle Ear
• Conduction
– Conduct sound from the outer ear to the inner ear
• Protection
– Creates a barrier that protects the middle and inner areas from
foreign objects
– Middle ear muscles may provide protection from loud sounds
• Transducer
– Converts acoustic energy to mechanical energy
– Converts mechanical energy to hydraulic energy
• Amplifier
– Transformer action of the middle ear
– only about 1/1000 of the acoustic energy in air would be
transmitted to the inner-ear fluids (about 30 dB hearing loss)
14. Eustachian Tube
• The eustachian tube connects the front wall of the middle
ear with the nasopharynx
• The eustachian tube also operates like a valve, which
opens during swallowing and yawning
• This equalizes the pressure on either side of the eardrum,
which is necessary for optimal hearing.
• Without this function, a difference between the static
pressure in the middle ear and the outside pressure may
develop, causing the eardrum to displace inward or
outward
• This reduces the efficiency of the middle ear and less
acoustic energy will be transmitted to the inner ear.
16. Middle Ear Muscles
• Tensor tympani
– Attached to malleus
– Innervated by V, trigeminal nerve
• Stapedius
– Attached to stapes
– Innervated by VII, facial nerve
• Middle Ear Muscle Function:
– Help maintain ossicles in proper position
– Protect inner ear from excessive sound
levels
• When ear exposed to sound levels above
70 dB, the muscles contract, decreasing
amount of energy transferred to inner ear
– This protective reflex termed "acoustic
reflex"
17. Ligaments of Middle Ear
• Function
– restrict and confine
the effect of ossicles
to act as a lever
– restrict movements to
reduce the chance of
damage to the inner
ear
– prevents distortion to
sound
21. Cochlea
• The cochlea resembles a
snail shell and spirals for
about 2 3/4 turns around
a bony column
• Within the cochlea are
three canals:
– Scala Vestibuli
– Scala Tympani
– Scala Media
23. • Oval window
• Scala vestibuli
• Scala tympani
• Secondary tympanic
membrane
• Contain perilymph
• Scala media or duct of
cochlea contains
endolymph
Cochlea
24. Scala Media
• Basilar membrane
• Spiral organ
• Hair cells of organ of
corti
• Tectorial membrane
• Single row of inner hair
cells
• Each one has 20 large
afferent
• Outer hair cells
32. Auditory Nerve
• Receptors are hair cells of
organs of corti
• Bipolar cells
• Cell bodies are in the spiral
ganglion on the
• Spiral lamina
• Auditory nerve attached to
lower border of pons
• Cerebellar-pontine angle
33. Auditory Pathway
• First order neurones end
on ventral and dorsal
cochlear nuclei
• On inferior cerebellar
peduncle
• 2nd order neurones
• Trapezoid body
• Lateral leminiscus
• Inferior colliculus
• Superior olivary nucleus
34. • Inferior colliculus
• Via inferior brachium
• Medial geniculate body
• 3rd order neurones
• Auditory radiations to
auditory cortex in temporal
lobe
Auditory Pathway
39. Receptors
• Sensory static receptors in
macula of the utricle and
saccule
• Cristae of the ampullae are the
end organs of the dynamic
movement semi circular canals
• Maculae respond to linear
acceleration of head in
horizontal or vertical plane
during walking
40. • Hair cells are found in the
macula discharge all the time
• Cilia on the hair cells
embedded in gelatinous
substance containing calcium
carbonate crystals
Receptors
