Download anatomy and physiology of the ear

ANATOMY AND PHYSIOLOGY
OF THE EAR
Yard.Doc.Dr.Müzeyyen Doğan
Learning goal and objectives of
the lesson
Learning goal of the lesson: The learner should know the basic
anatomic structures and physiology of external, middle and inner
ear
Learning objectives of the lesson the learner will be able to:
 identify the anatomic structures of the external, middle and inner
ear
 identify the physiology of the external, middle and inner ear
 identify the physiology of the hearing
 identify the physiology of the balance
Skill objectives the learner will be able to ear examination
OUTER EAR
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Consists of the auricle
and EAM
Skin-lined apparatus
Approximately 2.5 cm
in length
Ends at tympanic
membrane
OUTER EAR
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Auricle is mostly skinlined cartilage
External auditory
meatus
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Cartilage: ~40%
Bony: ~60%
S-shaped
Narrowest portion at
bony-cartilage junction
Anatomy and Physiology
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EAC is related to
various contiguous
structures
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Tympanic membrane
Mastoid
Glenoid fossa
Cranial fossa
Infratemporal fossa
Anatomy and Physiology
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Squamous epithelium
Bony skin – 0.2mm
Cartilage skin
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0.5 to 1.0 mm
Apopilosebaceous unit
The Middle Ear:
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A cleft within the
temporal bone
Lining is mucous
membrane
Tympanic Membrane
separates it from EAC
Eustachian tube
connects it to
nasopharynx
Also Connected to
Mastoid Air Cells
Middle Ear Structures
1234-
Malleus
Incus
--Ossicles
Stapes
Tympanic Membrane
(Eardrum)
5- Round Window
6- Eustachian Tube
Middle Ear Muscles
1. The Stapedius Attaches to Stapes,Contracts in
Response to Loud sounds, chewing, speaking; Facial (VIIth
cranial) nerve
2. The Tensor Tympani Helps open Eustachian tube
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
Middle Ear Functions
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Impedance Matching
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Filtering
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Acoustic Reflex
Impedance Matching
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The middle ear allows the impedance
matching of sound traveling in air to
acoustic waves traveling in a system of
fluids and membranes in the inner ear
Acoustic Reflex
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The movement of the ossicles
may be stiffened by two
muscles, the stapedius and
tensor tympani, which are
under the control of the facial
nerve and trigeminal nerve,
respectively. These muscles
contract in response to loud
sounds, thereby reducing the
transmission of sound to the
inner ear. This is called the
acoustic reflex
Middle Ear Transmits Energy by
Two Pathways:
MECHANISMS OF MIDDLE-EAR
GAIN
Acoustic Coupling
Ossicular Coupling
•
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Area Difference (TM to footplate)
Lever Action (Malleus to Incus)
Acoustic Coupling
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The collected pressure of sound vibration
that strikes the tympanic membrane is
therefore concentrated down to this much
smaller area of the footplate, increasing
the force but reducing the velocity and
displacement, and thereby coupling the
acoustic energy.
Anatomy and Physiology
•Ossicular Amplifier System
MIDDLE-EAR GAIN
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The ossicles are classically supposed to
mechanically convert the vibrations of the
eardrum, into amplified pressure waves in
the fluid of the cochlea (or inner ear) with
a lever arm factor of 1.3. Since the area of
the eardrum is about 17 fold larger than
that of the oval window, the sound
pressure is concentrated, leading to a
pressure gain of at least 22.
Function of Middle Ear
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Conduction
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Protection
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Creates a barrier that protects the middle and inner areas
from foreign objects
Middle ear muscles may provide protection from loud sounds
Transducer
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Conduct sound from the outer ear to the inner ear
Converts acoustic energy to mechanical energy
Converts mechanical energy to hydraulic energy
Amplifier
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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)
Ear
INNER EAR
INNER EAR :
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Cochlea – hearing
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Vestibule – static equilibrium
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Semicircular canals – dynamic
equilibrium
OHC vs. IHC Function
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Vestibulocochlear nerve – cranial nerve VIII
Audible range: 20 -- 20,000 hertz
Ossicles amplify sound 22 X
Some nerve fibers cross over to opposite side of brain
Hair Cells
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Outer Hair
Cells
Inner Hair
Cells
OHC
movie
OCH Cilia Theory: Tip-links
<<<IHC
OHC >>>
Equilibrium – Balance
Static equilibrium – maintenance of body
posture relative to gravity while the body is
still.
Dynamic equilibrium – maintenance of
the body posture (mainly the head) in
response to sudden movements. Tracking
a moving object.
Static Equilibrium
Inside the vestibule are two chambers :
utricle and saccule.
Regions of hair cells and supporting cells
called maculae.
Otoliths – “ear rocks”
Dynamic Equilibrium
Semicircular canals
In ampulla is the crista ampullaris –
contains hair cells and supporting cells
covered by a gelatinous mass called the
cupula.
Neurological connections between eyes
and semicircular canals – for tracking
Nystagmus