Transcript 24.The ear2009-01

Dr. Ahmed Fathalla Ibrahim
THE EAR
•
•
1.
2.
3.
Is an organ of hearing & balance
Consists of three parts:
External Ear
Middle Ear
Internal Ear
THE EXTERNAL EAR
• AURICLE
• EXTERNAL
AUDITORY
MEATUS
AURICLE:
• Shape: consists of a
thin plate of elastic
cartilage
• Function: collects
air vibrations
• Motor supply: facial
nerve
EXTERNAL AUDITORY MEATUS
• Shape: a curved
tube formed of
elastic cartilage
(outer 1/3) &
tympanic plate of
temporal bone
(inner 2/3)
• Function: conducts
sound waves from
auricle to tympanic
membrane
THE MIDDLE EAR
(TYMPANIC CAVITY)
•
Definition: air-containing cavity in
petrous part of tympanic bone, lined
with mucus membrane
• Function: transmits vibration of
tympanic membrane to perilymph of
internal ear
• Communications:
1. Anteriorly: with nasopharynx (through
auditory tube)
2. Posteriorly: with mastoid antrum
3. Nerve supply: tympanic branch of
glossopharyngeal nerve
THE MIDDLE EAR
• Roof: tegmen typani
(thin plate from
petrous temporal
bone), separates
middle ear from
temporal lobe of
brain
• Floor: thin plate of
bone, separates
middle ear from
superior bulb of
internal jugular vein
THE MIDDLE EAR
• Anterior wall:
1. Superiorly: has 2
openings (for
auditory tube & for
canal of tensor
tympani)
2. Inferiorly: thin plate
of bone separating
middle ear from
internal carotid
artery
THE MIDDLE EAR
• Posterior wall:
1.Superiorly: has
an opening
(aditus to mastoid
antrum)
2.Inferiorly: a
conical projection
(pyramid) for
emergence of
stapedius
•
THE MIDDLE EAR
Lateral wall: tympanic
membrane
•
Medial wall:
1. Promontory: rounded
projection formed by cochlea
2. Fenestra vestibuli: oval
opening, above & behind
promontory, closed by base of
stapes
3. Fenestra cochleae: round
opening below promontory,
closed by secondary tympanic
membrane
4. Prominence for facial nerve
canal: runs backward above
promontory & fenestra vestibuli
then curves downward behind
pyramid
THE TYMPANIC MEMBRANE
• Shape: a thin fibrous
membrane between
external & middle ear,
has a small depression
(umbo) produced by
handle of malleus,
divided into pars
flaccida & pars tensa
• Nerve supply:
• Outer surface:
auricular branch of
vagus
• Inner surface:
tympanic branch of
glossopharyngeal
AUDITORY OSSICLES
MALLEUS:
• Head: articulates with
body of incus
• Neck
• Handle: firmly attached
to medial surface of
tympanic membrane,
receives insertion of
tensor tympani
• Anterior process
• Lateral process:
attached to anterior &
posterior malleolar folds
of tympanic membrane
AUDITORY OSSICLES
INCUS:
• Body: articulates
with head of malleus
• Long process:
articulates with
head of stapes
• Short process:
attached to
tympanic cavity
AUDITORY OSSICLES
STAPES:
• Head: articulates
with long process of
incus
• NecK: receives
insertion of
stapedius
• Base: attached to
fenestra vestibuli
MUSCLES OF OSSICLES
TENSOR TYMPANI:
• Origin: auditory tube
• Insertion: handle of malleus
• Nerve supply: mandibular of trigeminal
• Action: damps down vibration of tympanic
membrane
STAPEDIUS:
• Origin: pyramid
• Insertion: neck of stapes
• Nerve supply: facial
• Action: damps down vibration of stapes
FACIAL NERVE
•
Course: runs in facial canal
then emerges through
stylomastoid foramen
• Branches:
1. Nerve to stapedius
2. Chorda tympani: carries
taste fibers from anterior 2/3
of tongue & preganglionic
parasympathetic fibers to
submandibular & sublingual
salivary glands
3. Greater petrosal nerve:
carries taste fibers from soft
palate & preganglionic
parasympathetic fibers to
lacrimal, nasal & palatine
glands
THE INTERNAL EAR
• Lies in petrous part of temporal
bone
• Consists of:
1. Bony labyrinth
2. Membranous labyrinth
BONY LABYRINTH
•
1.
2.
3.
•
Consists of:
Vestibule
3 semicircular canals
Cochlea
They are cavities
inside bone, filled
with perilymph in
which membranous
labyrinth is
suspended
MEMBRANOUS LABYRINTH
•
Lodged within bony
labyrinth
• Filled with endolymph
& surrounded by
perilymph
• Consists of:
1. Utricle & saccule: in
vestibule
2. 3 semicircular ducts: in
semicircular canals
3. Cochlear duct: in
cochlea
VESTIBULOCOCHLEAR NERVE
• Divides into:
1. Vestibular nerve: supplies utricle,
saccule & semicircular ducts
2. Cochlear nerve: supplies cochlear
duct