Download Parts Of the Ear

INTRODUCTION TO
AUDIOLOGY (SPHS 1100)
WEEK 3 POWER POINT
TOPICS
 ANATOMY OF EAR
 PHYSIOLOGY OF EAR
GOALS and OBJECTIVES
GOAL
Learner will understand the different topics related to
Audiology.
OBJECTIVES
 TLW understand the anatomy and physiology of the
ear. (cognitive)
Ear Diagram
ANATOMY OF EAR
Parts Of the Ear
The Human ear is divided in to three main parts
 Outer Ear
 Middle Ear
 Inner Ear
Outer Ear
 The outer ear is the visible part of the ear.
 The outer ear comprises a shell like-protrusion from
each side of the head, a canal through which sounds
travel, and the eardrum membrane.
 Eardrum membrane is called as Tympanic membrane.
 It consists of three parts
1. The Auricle (pinna ).
2. The External Auditory Canal.
3. The Tympanic Membrane
The Human Pinna and its
landmarks (auricle)
Outer Ear
The Auricle
 The auricle is the most visible part in the outer-ear
mechanism.
 It varies in size and shape from person to person.
 The funnel-like shape plays an important role on
gathering sound waves from the environment.
 The auricle is made of cartilage, with a number of
twists, turns and indentations.
 The cartilage is covered with skin.
 The bottom-portion of the auricle is lobule or ear lobe.
Outer Ear
 The outer rim of the auricle folds outwardly forming
helix.
 Antitragus is above the lobule.
 Antihelix is the elevation which is close to the center of
auricle.
 A small triangular protrusion which points backwards
and forms the anterior portion of the auricle is called
the tragus.
 Depression of the tragus in to the opening of the
external ear canal is an efficient means of blocking
sounds.
Outer Ear
 The occlusion is more efficient than plugging the ear
with a finger, clasping the hands over the auricle, and
even using some earplugs specifically designed for
sound attenuation.
 The middle portion of the outer-ear, before opening
the head is called the concha.
 Concha is bowl shaped and it is divided in to the
lower cavum concha and the upper cyber concha.
 The auricle is more efficient at delivering highfrequency sounds than low-frequency sounds.
 It helps on localization of sounds delivered to head.
Outer Ear
The External Auditory Canal (EAC)
 The external auditory canal is a tube formed in the
side of the head, which begins at the concha and
extending inward at a slight upward angle for
approximately 1 inch in adults.
 EAC is elliptical in shape and averages about 9mm in
height and 6.5 mm in width.
 The outer portion of the external auditory canal passes
through cartilage.
 The skin of EAC supports several set of glands such as
sebaceous glands.
Cross section of the external
ear
Outer Ear
 Sebaceous glands secrete an oily and fatty substance
which is called sebum.
 The major product of these secretions is earwax, or
cerumen.
 Cerumen exists the ear naturally when the walls of the
EAC are distorted by movement of the jawbone
during chewing and speaking.
 The outer third of the EAC contains a number of hair
follicles.
 Cerumen and hairs helps to keep foreign objects from
passing into the inner two-thirds of the canal.
Outer Ear
 The inner area of the EAC passes through tympanic
portion of the temporal bone.
 There are no glands and hair in this area.
 The two portions of the EAC meet at the
osseocartilaginous junction.
 The condyle which a protrusion of mandible comes to
rest just below the osseocartilaginous junction when
the jaw is closed.
 If the mandible override its normal position ,the
condyle will press into the junction causing pain and
this pain is called TemporoMandibularJoint (TMJ).
Outer Ear
 The angle of EAC is different in small children
compared to adults.
 The canal angles downward, rather than upward and
it is a more acute angle.
 Children’s ear can be examined from above the head
because of the above reason.
Tympanic Membrane
Outer Ear
 Tympanic Membrane
 The external auditory canal ends in a concave disklike structure called the tympanic membrane.
 It is also called as Ear Drum.
 The tympanic membrane acts as border between
outer ear and middle ear.
 The total area is about 63.3 mm2 (Harris, 1986).
 It is constructed of three layers.
 The outer layer is osseous.
 The middle layer is tough, fibrous, connective tissue,
Outer Ear
which contributes most of the membrane’s ability to
vibrate with impinging sound.
 The middle ear space behind the tympanic
membrane is lined with mucous membrane, including
the third layer of the tympanic membrane.
 The tympanic membrane is thin averaging about
0.07mm.
 According to Harris (1986) movement of one-billionth
of a centimeter is sufficient to produce a threshold
response in normal hearing individuals in the 800 to
6000HZ range.
Middle Ear
Middle Ear
 The middle ear is a space behind the eardrum and it
is roughly 2 cm3.
 The roof of the middle ear is a thin layer of bone,
separating the middle-ear cavity from the brain.
 Jugular bulb is below the floor of the middle ear and
behind the anterior wall is the carotid artery.
 The labyrinth of the inner ear lies behind the medial
wall .
 Mastoid process is beyond the posterior wall.
 The space in the middle ear above the tympanic
membrane is called epitympanic recess.
Middle Ear
 Middle ear is separated from the external auditory
canal by the tympanic membrane.
 It is connected to nasopharynx via the eustachian
tube.
 Middle-Ear Cleft comprises of the eustachian tube
and middle ear.
 The middle-ear cleft is lined with mucous membrane.
 The mucous membrane is ciliated and topmost cells
contain cilia.
 The motion of cilia creates a wiping action which
helps to cleanse the middle ear by moving particles
down and out of Eustachian tube.
Middle Ear
 The Eustachian Tube
 The Eustachian tube enters middle ear anteriorly at a
30 degree angle and passes down in to nasopharynx
for a distance of about 36 millimeters.
 The Eustachian tube opens during yawning, sneezing,
or swallowing and when excessive air pressure is
applied from the nose.
 Eustachian tube opens about once per minute when
we are awake and an average of once every five
minutes during sleep.
 The Eustachian tube is shorter and wider in length in
children compared to adults.
Middle Ear
 The orifice of the Eustachian tube in the nasopharynx
remain to open in infants till 6 months of age.
 The air pressure of middle ear must match that of the
external auditory canal to keep the pressure equal on
both sides of the tympanic membrane in order to
increase its mobility.
 The major reason for the need of pressure equalization
system is the absorption of air by middle-ear tissues.
Middle Ear
The Mastoid
 Some of the bones of the skull which surround the ear
are not solid and they are honeycombed with
hundreds of air cells.
 Each of these cells is lined with mucous membrane
and they are similar to that of the middle-ear cleft.
 These cells form the pneumatic mastoid of the
temporal bone.
 The middle ear opens up, back and upward in an
area called audits ad antrum.
 The mastoid process is the bony process behind the
auricle .
Middle Ear
Windows of the Middle Ear
 There are two windows in middle ear .
1. Oval window
2. Round Window
 The section of the bony portion of the inner ear
extends to the middle ear space and this protrusion is
called the promontory.
 The promontory separates two connections between
the middle and inner ear.
 Oval window is above promontory and below is the
round window.
Middle Ear
 The round window is covered by a very thin, tough
and elastic membrane.
 The oval window is filled by a membrane which
supports the base of stapes.
Middle Ear
Bones in the Middle Ear
 Middle ear contains three small bones which are
called as ossicles.
1. Malleus
2. Incus
3. Stapes
 The manubrium of the malleus is embedded in the
fibrous layer of the tympanic membrane.
 Manubrium extends from the upper portion of the
tympanic membrane to its approximate center.
Middle Ear
 The head of malleus is connected to the body of the
incus.
 The incus has a long process or crus which turns
abruptly to a very short crus, the lenticular process.
 The end of lenticular process sits on stapes.
 The stapes consists a head, neck, and two crura.
 The posteriors crus is longer and thinner than the
anterior crus.
 The base or footplate of the stapes occupies the
space in oval window.
Middle Ear
 The inward and outward movement of the umbo of
the tympanic membrane causes malleus and incus to
rotate, which transfers this force to the stapes.
 This movement in turn results in the inward and
outward motion of the oval window.
 Vibrations of the tympanic membrane are conducted
along the ossicular chain to the oval window.
 The chain acts like a single unit when transmitting
sounds above 800HZ.
The Middle-Ear Impedance
Matcher
 The average adult tympanic membrane is 85 to 90
mm2,but the effective vibrating area is only 55mm2.
 The vibrating area is 17 times that of the oval window.
 The sound pressure collected over the larger area of
the tympanic membrane is focused on the oval
window.
 The mass of the ossicular chain is poised to take
advantage of the physical laws of leverage.
 The ossicular chain rocks back and forth on an axis
and the action of the stapes in the oval window is like
a pivot.
The Middle-Ear Impedance
Matcher
 The combined effects of increased pressure and the
action of the malleus result in a pressure increase at
the oval window 23 times what it would be if airborne
sound impinged on it directly.
Inner Ear
Inner Ear
 The inner ear contains the sensory organs for hearing
and balance.
 It is made up of two parts, the cochlea and the
vestibular system.
 The cochlea deals with hearing where as the
vestibular system affects balance.
 The bony shaped structure like a snail in the inner ear is
cochlea.
 It is filled with endolymph and perilymph fluids.
 The organ of corti is the sensory receptor inside the
cochlea which holds the hair cells.
Inner Ear
The vestibular Mechanism
 The membranous sacs with in the vestibule are called
the utricle and the saccule.
 These two sacs are surrounded by perilymph and
contain fluid called endolymph.
 The saccule is smaller than the utricle.
 The end organ for balance is located at the bottom of
the utricle.
 The end organ within saccule is located on side on the
side.
Inner Ear
 Semicircular canals arise from utricle.
 They are membranous, containing endolymph and
surrounded in a larger bony cavern by perilymph.
 Three semicircular canals returns to the utricle through
enlarged areas called ampullae.
 Each ampulla contains an end organ for the sense of
equilibrium.
 The semicircular canals are arranged per-pendicular
to one another to cover all dimensions in space.
 The semicircular canals are the receptors for angular
acceleration.
Inner Ear
The Auditory Mechanism
 Vestibule communicates with a snail-like shelled
called the cochlea.
 Cochlea is made up of a twisting bony shell about
1cm wide and 5 mm from base to apex in humans.
 Scala vestibule is a part behind the oval window.
 At the bottom of the cochlea, the scala tympani is
visible which begins at round window.
 Both of these canals contains perilymph which is
continuous through a small passageway at the apex
of the cochlea called the helicotrema.
Inner Ear
 The canal between scala vestibule and scala tmypani
is scala media.
 Scala media is filled with endolymph and it is
continuous through the ductus reuniens with the
endolymph contained in the saccule, utricle, and
semicircular canals.
 The scala media is separated from the scala vestibule
by Reissners’ membrane and from the scala tmypani
by the basilar membrane.
 The organ of corti which is the end organ of hearing
extends along the full length of the scala media.
Inner Ear
 Basilar Membrane
 It is about 35 mm long and varies in width from less
than 0.1 mm at the basal to turn about 0.5 mm at the
apical turn .
 Three to five parallel rows of 12,000 to 15,000 outer hair
cells and one row of 3,000 inner hair cells are located
on the basilar membrane.
 Cortis’ arch separates outer and inner hair cells.
 The auditory nerve endings are located on the basilar
membrane.
References
 Images
https://www.studyblue.com/notes/note/n/final/deck/492
5488
https://ostranderbellepoint.wordpress.com/2013/03/30/e
ars-are-strange/
http://biologyforums.com/index.php?action=gallery;sa=view;id=6155
http://news.stanford.edu/news/2013/august/ear-boneconduction-080513.html
http://patient.info/health/dizziness