Download REVISIT ANATOMY OF EAR THE EXTERNAL EAR PINNA cont.

REVISIT ANATOMY OF EAR
LEARNING OBJECTIVES
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At the end of this class the student should be able to,
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Discuss the division of ear in parts.
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Understand the parts of external ear.
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Understand the parts of middle ear.
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Understand the parts of internal ear.
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Consists of auricle or pinna and external acoustic meatus.
THE EXTERNAL EAR
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PINNA: Crumpled plate of elastic cartilage covered by skin.
LOBULE: Lower part and soft part of ear, consists of
connective tissue covered by skin.
CONCHA: Is large depression which leads in to external
acoustic meatus.
INTRINSIC MUSCLES:Which can alter the shape of ear.
EXTERNAL MUSCLES: Move ear (are rudumentary in human).
PINNA cont.
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Blood supply: Posterior auricular artery and superior temporal artery.
Lymphatic drainage:
Preauricular and posterior auricular and superficial temporal lymph
nodes.
Nerve supply:
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Upper two third of lateral surfaceauriculotemporal nerve and lower
one thirds by greater auricular nerve.
Medial surface upper two third by lesser occipital nerve and lower one
third by greater auricle nerve.
Root of auricle by is supplied by branches of facial nerve.
EXTERNAL ACOUSTIC MEATUS
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Conducts sound waves.
“S” shaped.
About 3cm in length.
It is straightened for examination by pulling
upwards backwards and slightly laterally.
Anterior wall and floor are longer than posterior
wall and roof.
Medial third is bony and lateral two thirds is cartilaginous.
EXTERNAL ACOUSTIC MEATUS
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BONY PART:
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“C” shaped in cross section.
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Cartilaginous part:
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Also “C” shaped in section gap is filled by fibrous tissue.
Lined by thin skin firmly adherent to periosteum.
Anteriorly formed by tympanic part of temporal bone.
Posterosuperior part is formed by squamous temporal
bone.
Skin is adherent to the perichondrium.
Contains sebaceous gland and ceruminous glands (modified sweat
glands).
EXTERNAL ACOUSTIC MEATUS
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Blood supply: Outer part by superficial temporal and posterior
auricular arteries. Inner part by deep auricular branch of maxillary
artery.
Lymphatic drainage:
Preauricular, postauricular and superficial cervical lymph nodes.
Nerve supply:
Anterior half by auriculotemporal nerve and posterior half by auricular
branch of vagus.
THE MIDDLE EAR
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Middle ear or Tympanic cavity is about 15 mm in
anteroposterior and vertical diameter.
Shape of a biconcave lens.
The lateral wall:Is largely occupied by the
tympanic membrane.
Tympanic membrane extends upwards for 10 mm
from the floor and also bulges inwards.
Above the membrane the temporal bone is hollowed out into the
epitympanic recess.
THE TYMPANIC MEMBRANE
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Thin fibrous structure.
Circular.
1cm in diameter.
Covered externally: By thin layer of stratified
squamous epithelium (consists of collagen fibers).
Lies obliquely at 55 degree with the external acoustic meatus.Facing
downward forward and laterally.
Concave towards the meatus.
At the depth of the concavity is a small depression, the umbo.
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Cone of light (is at anteroinferior quadrant).
THE TYMPANIC MEMBRANE
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The handle of the malleus is firmly attached to the inner
surface of membrane.
From the lateral process of the malleus two thickened
fibrous folds (mallear folds) diverge up to the margins of
the tympanic bone between them is pars
flaccidasharpnell’s membrane. (crossed internally by the chorda
tympani).
Pars tensa. (It is held tensa by the inward pull of the tensor tympanic
muscles).
The tympanic membrane is thickened at its circumference and
slotted into a groove in the tympanic plate.
THE TYMPANIC MEMBRANE
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BLOOD SUPPLY: Deep auricular artery from maxillary artery on the
meatal side and stylomastoid artery from posterior auricular artery on
the mucosal surface forms a circular anastomosis with the anterior
tympanic branch of the maxillary artery round the margin of the
membrane
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NERVE SUPPLY: on the meatal surface: auriculotemporal nerve
supplemented by the vagus and on the mucosal surface: Tympanic
branch of the glossopharyngeal nerve via the tympanic plexus.
THE MEDIAL WALL OF THE TYMPANIC CAVITY
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Is also lateral wall of the internal ear. The promontory (first turn of the
cochlea and indented with fine grooves by the tympanic plexus.
Above it is a horizontal ridge for the canal for the facial nerve, and
immediately above that is the (horizontal) bulge due
to the lateral semicircular canal.
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Above and behind the promontory is the oval window
the fenestra vestibuli (closed in life by the foot piece
of the stapes).
Below and behind the promontory is the round
window the fenestra cochleae closed in life by the
fibrous secondary tympanic membrane.
THE ROOF OF THE TYMPANIC CAVITY
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Tegmen tympani (petrous bone that roofs also the
canal for the tensor tympanic and the tympanic
antrum.
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THE FLOOROF THE TYMPANIC CAVITY
Is a thin plate of bone above the jugular fossa.
At the anterior end is the internal opening of the tympanic canaliculus.
(for tympanic branch of the glossopharyngeal nerve).
THE ANTERIOR WALL OF THE TYMPANIC CAVITY
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Shortend by approximation of roof and floor.
It is perforated by the opening of two canals.
Lower is the bony part of the auditory tube.
Upper is the canal for the tensor tympani muscle.
Lower part of this wall forms the posterior wall of the
carotid canal (perforated by tympanic branches of the
internal carotid artery and sympathetic fibers from the internal carotid
plexus)
THE POSTERIOR WALL OF THE TYMPANIC CAVITY
Is deficient above, where there is an aperture, the aditus, which lead
back in to the tympanic antrum.
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Below the aditus a hollow cone, the pyramid, projects
in to the tympanic cavity.
Apex is perforated by the tendon of stapedius.
TYMPANIC ANTRUM
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Small, circular, air filled space, situated in the posterior part of the
petrous part of the temporal bone.1 cm in size, is of adult size at birth.
Superiorly.
Tegmen tympani. Beyond it is temporal lobe of
cerebrum.
Inferiorly.
Mastoid process with mastoid air cells.
Anteriorly.
Communicates with epitympanic recess through aditus.
Posteriorly.
Separated from sigmoid sinus by thin plate of bone.
Medially.
Petrous temporal bone.
Laterally.
Squamous temporal bone. Relation with suprameatal triangle).
CONTENTS OF MIDDLE EAR CAVITY
1. Ossicles– malleus, incus, stapes
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2. Muscles – tensor tympani, stapedius
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3. Vessels and nerves – chorda tympani and
tympanic plexus of ear.
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FUNCTIONS OF MIDDLE EAR CAVITY
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Narrow, oblique, slit like, air containing cavity in the petrous part of
temporal bone.
Transmit the vibrations of tympanic membrane to the perilymph of
internal ear.
OSSICLES
1. MALLEUS
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The malleus or hammer is a hammer-shaped bone
Connected with the incus and is attached to the inner surface of the
tympanic membrane
It transmits the sound vibrations from the eardrum to the incus.
2. INCUS
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The incus or anvil is the anvil-shaped small bone.
It connects the malleus to the stapes
The incus transmits sound vibrations from the malleus to the stapes.
MUSCLES
STAPEDIUS
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The stapedius is the smallest skeletal muscle in the
human body. At just over one millimeter in length, its
purpose is to stabilize the smallest bone in the body,
the stapes.
The stapedius emerges from a pinpoint foramen in
the apex of the pyramidal eminence (a hollow, coneshaped prominence in the posterior wall of the
tympanic cavity), and inserts into the neck of the stapes.
Innervated by the nerve to stapedius, a branch of cranial nerve VII, the
facial nerve.
MUSCLES
TENSOR TYMPANI
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The larger of the two muscles of the tympanic cavity, is
contained in the bony canal above the osseous portion
of the auditory tube.
Its role is to dampen sounds, such as those produced
from chewing.
It arises from the cartilaginous portion of the auditory
tube and the adjoining part of the great wing of the sphenoid
Inserted into the handle (manubrium) of the malleus, near its root.
AUDITORY TUBE
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Is the channel through which the tympanic cavity communicates with
the nasal part of the pharynx.
35 mm long (in adults).
Extends from the anterior wall of the middle ear to the lateral wall of
the nasopharynx.
Has two parts
Osseous part
Cartilagenous part
ARTERIES OF MIDDLE EAR
Anterior tympanic branch (maxillary artery)
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Superior tympani (middle meningeal artery) and petrosal branch
Posterior tympani (posterior auricular artery)
Inferior tympanic (ascending Ph artery)
Tympanic branch from artery of pterygoid canal.Coticotympanic from
I.C artery
VEINS AND LYMPH NODES OF MIDDLE EAR CAVITY Pterygoid
plexus of veins which drain into superior petrosal sinus.
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LYMPH NODES:Periauricular and retro pharyngeal nodes
NERVE SUPPLYTympanic branch of glossopharyngeal nerve
(tympanic plexus). Superior and inferior corticotympanic nerves from
the sympathetic plexus around internal carotid artery.
INTERNAL EAR
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All these structures are in the petrous part of the
temporal bone between the middle ear laterally
and the internal acoustic meatus medially.
PARTS OF INTERNAL EAR
INTERNAL EAR CONSISTS OF:
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Bony labyrinth
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Vestibule,
Three semicircular canals
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Cochlea
Membranous labyrinth.
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Semicircular ducts
Cochlear duct
Two sacs (utricle and saccule).
• These bony cavities are lined with periosteum and contain a clear fluid
the perilymph.
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spaces are filled with endolymph.
FUNCTION OF INTERNAL EAR
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The internal ear converts the mechanical signals
received from the middle ear, which start as sound
captured by the external ear, into electrical signals to
transfer information to the brain.
The internal ear also contains receptors that detect motion and
position.
INTERNAL EAR
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The structures in the internal ear convey information
to the brain about balance and hearing:
Cochlear duct is the organ of hearing
Semicircular ducts, utricle, and saccule are the
organs of balance.
The nerve responsible for these functions is the vestibulocochlear
nerve [VIII], which divides into vestibular (balance) and cochlear
(hearing) parts after entering the internal acoustic meatus.
BONY LABYRINTH
Vestibule:
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It is the central part of the bony labyrinth.
contains the oval window in its lateral wall
It communicates anteriorly with the cochlea and
posterosuperiorly with the semicircular canals.
A narrow canal (the vestibular aqueduct) leaves the vestibule, and
passes through the temporal bone to open on the posterior surface of
the petrous part of the temporal bone.
BONY LABYRINTH
Semicircular Canals
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Projecting in a posterosuperior direction from the vestibule are three in
number
– Anterior (superior) vertical
– Posterior (vertical)
– Lateral (horizontal)
Each of these canals forms two-thirds of a circle
connected at both ends to the vestibule and with
one end dilated to form the ampulla.
The canals are oriented so that each canal is at right angles to the
other two.
BONY LABYRINTH
COCHLEA
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It is a bony structure that twists on itself two and onehalf to two and three-quarter times around a central
column of bone (the modiolus).
This arrangement produces a cone-shaped structure
with a base of cochlea that faces posteromedially and
an apex that faces anterolaterally.
This positions the wide base of the modiolus near the internal acoustic
meatus, where it is entered by branches of the cochlear part of the
vestibulocochlear nerve [VIII].
BONY LABYRINTH
LAMINA OF MODIOLUS, OR SPIRAL LAMINA).
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Circling around the modiolus, and held in a central position by its
attachment to the lamina of modiolus, is the cochlear duct, which is a
component of the membranous labyrinth.
Cochlear duct creates 2 canals
– Scalavestibuli
– Continuous with the vestibule
– Scala tympani
– Separated from the middle ear by the secondary
tympanic membrane covering the round window
They extend throughout the cochlea and are continuous with each
other at the apex through a narrow slit (the helicotrema) .
COCHLEAR AQUEDUCT
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Near the round window is a small channel (the cochlear
canaliculus), which passes through the temporal bone
and opens on its inferior surface into the posterior cranial
fossa.
This provides a connection between the perilymph-containing cochlea
and the subarachnoid space.
MEMBRANOUS LABYRINTH
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It is a continuous system of ducts and sacs within the
bony labyrinth.
It is filled with endolymph and separated from the
periosteum that covers the walls of the bony labyrinth
by perilymph.
Consisting of
Two sacs (the utricle and the saccule) and
Four ducts (the three semicircular ducts and the cochlear duct).
The general organization of the parts of the membranous labyrinth
places:
ORGANS OF BALANCE
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5 of the 6 components of the membranous labyrinth are concerned
with balance. These are the:
Two sacs (the utricle and the saccule)
Three ducts (anterior, posterior, and lateral semicircular ducts).
Utricle
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The utricle is the larger of the two sacs. It is oval, elongated and
irregular in shape and is in the posterosuperior part of the vestibule of
the bony labyrinth.
Three semicircular ducts empty into the utricle.
Saccule
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The saccule is a smaller, rounded sac lying in the
anteroinferior part of the vestibule of the bony
labyrinth. The cochlear duct empties into it.
The utriculosaccular duct establishes continuity
between all components of the membranous labyrinth
and connects the utricle and saccule
ORGANS OF BALANCE
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Branching from utricosaccular duct is the endolymphatic duct, which
enters the vestibular aqueduct (a channel through the
temporal bone) to emerge onto the posterior surface
of the petrous part of the temporal bone in the
posterior cranial fossa.
Here the endolymphatic duct expands into the
endolymphatic sac, which is an extradural pouch.
Each semicircular duct is similar in shape, including a dilated end
forming the ampulla, to its complementary bony semicircular canal,
only much smaller.
SENSORY RECEPTORS
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Functionally, sensory receptors for balance are organized into unique
structures and in each of the components of the vestibular apparatus.
In the utricle and saccule this sense organ is the macula of utricle
and macula of saccule,
Ampulla of each of the three semicircular ducts it is the crista.
Utricle responds to centrifugal and vertical acceleration,
Saccule responds to linear acceleration.
Receptors in the three semicircular ducts respond to movement in any
direction.
ORGAN OF HEARING
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Triangular-shaped cochlear duct has:
An outer wall against the bony cochlea consisting of
thickened, epithelial-lined periosteum (the spiral
ligament).
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Roof (vestibular surface membrane)
which separates the endolymph in the cochlear duct from the perilymph in
the scalavestibuli and consists of a membrane with a connective tissue
core lined on either side with epithelium;
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Floor, which separates the endolymph in the cochlear duct from the
perilymph in the scala tympani and consists of the free edge of the
lamina of modiolus, and a membrane (basilar membrane) extending
from this free edge of the lamina of modiolus to an extension of the
spiral ligament covering the outer wall of the cochlea.
VESSELS
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Arterial supply to the internal ear is divided between vessels supplying
the bony labyrinth and the membranous labyrinth.
Bony labyrinth is supplied by the same arteries that supply the
surrounding temporal bone-these include
Anterior tympanic branch from the maxillary artery
stylomastoid branch from the posterior auricular artery
Petrosal branch from the middle meningeal artery.
MEMBRANOUS LABYRINTH
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LABYRINTHINE ARTERY, which either arises from the anterior
inferior cerebellar artery or is a direct branch of the basilar arterywhatever its origin, it enters the internal acoustic meatus with the facial
[VII] and glossopharyngeal [IX] nerves and eventually divides into
INNERVATION
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The vestibulocochlear nerve [VIII] carries special afferent fibers for
hearing (the cochlear component) and balance (the vestibular
component).
It enters the lateral surface of the brainstem, between the pons and
medulla, after exiting the temporal bone through the internal acoustic
meatus and crossing the posterior cranial fossa.
Inside the temporal bone, at the distal end of the internal acoustic
meatus, the vestibulocochlear nerve divides to form: the cochlear
nerve, and the vestibular nerve.
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INNERVATION
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The vestibular nerve enlarges to form the vestibular ganglion, before
dividing into superior and inferior parts, which distribute to the three
semicircular ducts and the utricle and saccule.
The cochlear nerve enters the base of the cochlea and passes
upwards through the modiolus.
The ganglion cells of the cochlear nerve are in the spiral ganglion at
the base of the lamina of modiolus as it
winds around the modiolus.
Branches of the cochlear nerve pass through
the lamina of modiolus to innervate the
receptors in the spiral organ.
THE END