anatomy of the ear the organ of hearing and equilibrium divided into three parts: external ear...
TRANSCRIPT
ANATOMY OF THE EAR
•The organ of hearing and equilibrium•Divided into three parts:
• External ear• Middle ear• Internal ear
External earIncludes:
• The Auricle and;• The External acoustic meatus
auricle External acoustic meatus
Middle earInternal ear
External ear
External EarAuricle
•Collects sound waves and Directs them into the external acoustic meatus•Formed of a thin plate of cartilage covered by skin•Has a lateral and medial surfaces•The lateral surface presents some elevations and depressions
Parts of the auricle:• Helix: the curved outer margin of the auricle
• Begins anteriorly at a ridge called the crus of helix• Ends postero-inferiorly at the lobule of the ear
• Antihelix: a cruved ridge in front of the posterior part of helix• Superiorly it divides into sup. & inf. crura• The crura are separated by the triangular fossa
• Scaphoid fossa: depression between helix and antihelix• Tragus: a projection below the crus of helix• Antitragus: a small tubercle on the lower part of antihelix• Concha : the central depression of the auricle
Superior & inferiorcrura of antihelix
Triangular fossa
Helix
Antihelix Crus of helix
TragusConcha
Lobule
Antitragus
Muscles of the auricle:Extrinsic muscles:•Auricularis anterior
Supplied by temporal branches of facial n.•Auricularis superior
•Auricularis posterior, supplied by post. auricular n. (from facial)
Intrinsic muscles: slips of striated muscle fibers, supplied by temporal and posterior auricular branches of facial n.
Arterial supply of the auricle:•Auricular branches of superficial temporal a.•Auricular branch of posterior auricular a.
Sensory nerve supply of the auricle:• Great auricular: supplies lower 1/3 of lateral surface &
lower 2/3 of medial surface• Auriculotemporal: supplies upper 2/3 of lateral surface• Lesser occipital: supplies upper 1/3 of medial surface
• Auricular branch of vagus: supplies skin of concha• Facial nerve: communicates with auricular branch of vagus
Auricularis posterior
Auricularis superior
Auricularis anterior
External acoustic meatus
External acoustic meatus
•The passage between the concha and the outer surface of tympanic membrane•Conducts sound waves from the auricle to the tympanic membrane•Measures 4 cm from the tragus (2.5 cm from bottom of concha)•The lateral 1/3 forms the cartilagenous part of the meatus•The medial 2/3 form the bony part of the meatus•The anterior wall and floor of the meatus are longer than the roof and post wall (because of the obliquity of the tympanic membrane)
•The meatus is S-shaped, and has 2 constrictions:• At the junction between the cartilagenous and bony parts• In the bony part (5mm from the tympanic membrane) called the isthmus
•The skin of the meatus is thin and firmly attached to its walls•The outer 1/3 contains hairs and seruminous glands (secrete ear wax)
Tympanic membrane
External acousticmeatus
Tympanic Membrane• An oval semitransparent membrane• Obliquely situated at the bottom of the external acoustic meatus• The circumference of the membrane is thickened and fitted into the
tympanic sulcus of temporal bone• The upper part of the sulcus is deficient forming a notch• Two fibrous bands connect the ends of the notch to the lateral
process of malleus (anterior & posterior malleolar folds)• Three parts of the membrane can be recognized:
• Pars flaccida: the triangular area between the malleolar folds• Pars tensa: the greater part of the membrane• Cone of light: at the antero-inferior part of the membrane
• The handle of malleus is attached to the center of the inner surface of the membrane leading to projection of the membrane towards the middle ear
• The membrane is concave laterally and convex medially
Lateral processof malleus
Handle ofmalleus
Posterior malleolarfold
Pars flaccida
Anterior malleolarfold
Lateral processof malleus
Handle ofmalleus
Cone oflight
External
acoustic meatus
Lateral view
anterior view
Layers of the tympanic membrane:• Outer cuticular layer• Middle fibrous layer• Inner mucous layer
Arterial supply of the external acoustic meatus:• Auricular branches of superficial temporal• Auricular branch of posterior auricular
•Arterial supply of the tympanic membrane:Outer surface:• Deep auricular (branch of maxillary)
Inner surface:• Anterior tympanic (maxillary)• Posterior tympanic (stylomastoid artery)• Carotico-tympanic (internal carotid artery)
Nerve supply of the external acoustic meatus:• Auriculotemporal n: supplies anterior wall and roof• Auricular branch of vagus: supplies floor and posterior wall
Nerve supply of the tympanic membrane:• Outer surface: same nerves which supply the external meatus• Inner surface: tympanic branch of glossopharyngeal
Nerve supply of the external ear:• Great auricular n:
-lower 1/3 of lateral surface of auricle-lower 2/3 of medial surface of auricle
• Lesser occipital n:-outer surface of tympanic membrane-upper 1/3 of medial surface of auricle
• Auriculotemporal n:-upper 2/3 of lateral wall of auricle-anterior wall and roof of meatus-outer surface of tympanic membrane
• Auricular branch of vagus:-concha of auricle-floor and posterior wall of ext. ac. meatus
Inner surface of tympanic membrane is supplied by
• tympanic branch of glossopharyngeal
Arterial supply of the external ear:• Auricular branches of superficial temporal a.
-lateral surface of auricle-external acoustic meatus
• Auricular branch of posterior auricular a.-medial surface of auricle-external acoustic meatus
• Deep auricular (of maxillary)-outer surface of tympanic membrane
Inner surface of tympanic membrane is supplied by:-Anterior tympanic (maxillary)-Posterior tympanic (stylomastoid)-Carotico-tympanic (internal carotid)
Summary of arterial & nerve supply of external ear
Middle Ear (Tympanic Cavity)
• A small irregular cavity inside the temporal bone, on the inner aspect of the tympanic membrane• Contains air conveyed to it from the nasopharynx through the auditory tube• Also contains 3 very small bones (ear ossicles), malleus, incus and stapes• The ear ossicles transmit sound vibrations from the tympanic membrane to the internal ear
Incus
Stapes
Epitympanic recess
Externalauditory meatus
Tympanic membrane
Auditory tube
malleus
Auditory tubeIJV
Tympanicmembrane
Externalauditory meatus
Anterior view
• The tympanic cavity is formed of 2 parts:-Tympanic cavity proper: the part medial to the tympanic membrane-Epitympanic recess: the part above the level of the tympanic membrane
• The tympanic cavity communicates posteriorly with the mastoid antrum, AND communicates anteriorly with the nasopharynx
Anterior viewMedial view
Auditory tube
External acousticmeatus Tympanic membrane
Epitympanic recess Malleus
IncusStapes
Walls of the Middle Ear
Roof: (tegmental wall)•Formed by the tegmen tympani: a thin plate of the petrous bone• It separates the middle ear from the middle cranial fossa
Floor: (jugular wall)•Formed by the jugular fossa, a thin plate of bone which separates the tympanic cavity from the superior bulb of IJV
Tegmen tympani
IJVAnterior view
Anterior wall: (carotid wall)• Its lower part is formed by the posterior wall of the carotid canal (the posterior wall of carotid canal is
perforated by the carotico-tympanic nerves and the carotico-tympanic branch of ICA)
• The upper part of the anterior wall presents two openings of two canals:- Canal for tensor tympani: transmits the tensor tympani to be inserted into the handle of malleus- Auditory tube: runs below the canal for tensor tympani
Chorda tympani
Facial nerve
Handle of malleusJugular fossaICA
Auditory tube
Tensor tympaniEpitympanic recess
Mastoid air cellsAditus to mastoid antrum
IJV
Medial view
ICA
Mastoid antrum
Posterior wall: (mastoid wall)The posterior wall shows the following features:• Aditus to the mastoid antrum: an aperture from the epitympanic recess to the mastoid antrum• Pyramid: a small hollowed pyramidal eminence, it contains the stapedius muscle. The base of the pyramid
is connected to the facial canal by an aperture which transmits the nerve to stapedius• Posterior canaliculus for the chorda tympani: Lies close to the lateral side of the pyramid and transmits
the chorda tympani from the facial canal to the middle ear.
Mastoid antrum
Pyramid
Chorda tympani
Facial nerve
Facial nerve
Tendon of stapedius muscle
Tensor tympani
Auditory tube
Tegmen tympani
Jugular fossa
Lateral View (tympanic membrane removed)
Lateral wall: (membranous wall)• Formed mainly by the tympanic membrane and partly by the lateral wall of epitympanic recess.• Presents the following features:
-Posterior canaliculus for chorda tympani-Anterior canaliculus for chorda tympani-Petrotympanic fissure (through which passes the anterior tympanic branch of maxillary a)
Medial view
Epitympanic recess
Anterior canaliculusfor chorda tympani
Tensortympani
Chorda tympani
Medial wall: (labyrinthic wall)• Formed by the lateral aspect of the internal ear. It presents the following features:
- Promontory: a rounded bulge formed by the basal turn of the cochlea. The surface of the promontory presents grooves lodging the tympanic plexus of nerves.- Oval (vestibular) window: a small opening above the promontory, it lodges the base of stapes- Round (cochlear) window: a small opening below the promontory closed by a delicate membrane called the secondary tympanic membrane- Prominence of facial canal: traverses the medial wall above the oval window.
Facial nerveICA
Promontory showingtympanic plexus of nerves
Auditory tube
Tensor tympani
Prominence of facial canal
Oval window closed by base of stapesTendon of stapedius
pyramid
Chorda tympani
Round window
Lateral view
Oval window(closed by base of stapes)
Promontory formed bythe basal turn of cochlea
Auditory tube
Round window closed bythe secondary tympanic membrane
Base of stapes
Prominence offacial canal
PosteriorMedial
Lateral
Anterior
Auditory Ossicles• Three very small bones which form a bony chain that transmits sound waves
from the tympanic membrane across the tympanic cavity to the oval window• They include: Malleus, Incus and Stapes
Malleus:• The largest of the three ossicles• Hammer-shaped, formed of a head, neck and three processes (the handle, anterior and lateral processes)• The head carries an articular facet for articulation with the body of incus• The anterior process gives attachment to the anterior ligament of malleus which connects it to the
petrotympanic fissure• The lateral process is attached to the tympanic membrane, and to the anterior and posterior malleolar
folds which connect it to the upper notch of the tympanic sulcus.• The handle is adherent to the tympanic membrane and receives the insertion of the tensor tympani
Medial view
Head of malleus Body of incus
Lateral process
Anterior process
Handle of malleus stapes
Incus:• Formed of a body and 2 processes (a long and a short process)• The body carries a facet for articulation with the head of malleus• The long process is directed downwards, its lower end bends
medially to articulate with the head of stapes• The short process is directed backwards
Head of malleusBody of incus
Short limb of incus
Long limb of incus
Head of stapes
Medial view
External acoustic meatus
malleus
incus
stapes
Tympanic membrane
Anterior view
Stapes:• Formed of a head, neck, two limbs and a base (footplate)• The head is directed laterally and articulates with the lower end of the long limb of incus.• The neck gives insertion to the tendon of stapedius• The base is lodged in the oval window on the medial wall of the middle ear.
Long limb of incus
Head of stapes
Ant & postlimbs of stapes
Base of stapes
Neck of stapes
External acoustic meatus
malleus
incus
stapes
Tympanic membrane
Medial view
Anterior view
Auditory Muscles
Tensor tympaniO: cartilaginous part of the auditory tube and
walls of the canal for tensor tympaniI: handle of malleusN: mandibular nerve (through a branch from the
nerve to medial pterygoid)
StapediusO: inner wall of the pyramidI: neck of stapesN: facial nerve (the nerve to stapedius arises in the facial canal)
Action of auditory muscles:• The tensor tympani pulls the tympanic membrane inwards• The stapedius pulls the stapes outwards• The two muscles contract in response to sounds of high
intensity to lessen the transmission of sound waves to the oval window
Handle of malleus
Tendon oftensor tympani
PyramidTendon of stapedius
Neck of stapes
Lateral view
External auditorymeatus
Anterior view
Mastoid antrumAn air sinus which comuunicates with the post part of epitympanic recess through an aditus
Relations of the mastoid antrum:• Anterior wall: communicates with the epitympanic recess through the aditus• Posterior wall: sigmoid sinus and mastoid air cells• Roof: tegmen tympani• Floor: mastoid air cells• Lateral: suprameatal triangle of temporal bone• Medial: posterior semicircular canal
Medial view
Auditory (Pharyngotympanic) Tube
• A mucous lined canal (36mm long) connecting the tympanic cavity with the nasopharynx• From the anterior wall of the tympanic cavity, the canal is directed downwards, forwards and medially• Its lateral 1/3 is bony, while its medial 2/3 are cartilagenous• The widest part of the tube is at its opening in the nasopharynx• Its narrowest part is at the junction of the bony and cartilaginous parts• The tube equalizes pressure on both sides of the tympanic membrane
Auditory tube(cartilaginous part)
Facial NerveCourse• Leaves the cranial cavity by passing into the internal acoustic meatus• Pierces the bottom of the meatus and enters into the facial canal• Runs laterally above the vestibule of internal ear until it reaches the medial wall of the tympanic cavity• Bends sharply backwards above the promontory forming the geniculum of the facial nerve• Continues backwards forming a prominence in the medial wall of the middle ear.• Reaches the posterior wall of the middle ear and descends vertically behind the pyramid to emerge from
the stylomastoid foramen
pyramid Tendonof stapedius
Prominenceof facial canal
Vestibular window
geniculum
Greater petrosal n
Facial nerve
Promontory &tympanic plexus
Chorda tympani
Lateral viewSuperior view
Branches of the Facial NerveCommunicating branches:• In the internal acoustic meatus: With the stato-acoustic nerve• From the geniculate ganglion:
a. external petrosal (joins the sympathetic plexus around the middle meningeal artery)b. greater petrosal (joins the sphenopalatine ganglion)c. a twig which joins the lesser petrosal (to the otic ganglion)
• In the facial canal: communicates with the auricular branch of vagus
Branches of distribution:In the facial canal:• Nerve to stapedius: arises in the facial canal, passes into the pyramid to supply the stapedius m.• Chorda tympani:Below the stylomastoid foramen• Posterior auricular n: arises just below the stylomastoid foramen• Digastric branch: arises just below the stylomastoid foramen and supplies the post belly of digastric• Stylohyoid branch: arises just below the stylomastoid foramen and supplies the stylohyoid m.• Terminal branches in the face:
- Temporal - Zygomatic - Buccal - Marginal mandibular - Cervical
Chorda tympani:• Arises in the facial canal 6mm above the
stylomastoid foramen• Enters the tympanic cavity through a canaliculus
in its posterior wall• Runs forwards through the tympanic cavity
between the fibrous and mucous layers of the tympanic membrane
• Leaves the tympanic cavity through a canaliculus in its anterior wall (med to the spine of sphenoid)
• Reaches the infratemporal fossa and joins the lingual nerve
• Carries taste fibers from the ant 2/3 of the tongue and preganglionic parasympathetic fibers to the submandibular and sublingual salivary glands
Chorda tympani
Tympanic nerve:• A branch from the glossopharyngeal just below the jugular foramen• Enters the floor of the tympanic cavity through the tympanic canaliculus• Joins the tympanic plexus on the promontory• The tympanic plexus gives rise to the lesser petrosal nerve• The lesser petrosal leaves the cranial cavity through the foramen ovale and joins the otic ganglion• It carries preganglionic parasympathetic fibers to the otic ganglion
Greater petrosal
Tympanic plexus
Jugular fossa
Tympanic nerve
Geniculate ganglion
Arterial supply of the middle ear:• Anterior tympanic artery: from the first part of maxillary a (ECA)• Stylomastoid artery: from the post auricular or occipital a (from ECA)• Carotico-tympanic artery: from the ICA in the carotid canal• Superior tympanic artery: from the ascending pharyngeal a (ECA)• Inferior tympanic artery: from the middle meningeal artery• Petrosal branch of middle meningeal artery• A twig from the artery of pterygoid canal: from the third part of maxillary a
Venous drainage of the middle ear:•Pterygoid plexus of veins•Superior petrosal sinus
Nerve supply of the middle ear:• Nerves which supply the middle ear form the tympanic plexus on the promontory• The tympanic plexus is formed of:
- Tympanic nerve: from the glossopharyngeal nerve- Superior caroticotympanic nerve: from the sympathetic plexus around ICA- Inferior caroticotympanic nerve: from the sympathetic plexus around ICA
• Both carotico-tympanic nerves pierce the posterior wall of the carotid canal to enter the middle ear
• The tympanic plexus gives the following branches:- Lesser petrosal nerve: the motor root to the otic ganglion- Twigs to the mucosa of tympanic cavity, auditory tube, mastoid antrum and mastoid air cells- Communicating branch to the greater petrosal nerve
Facial Nerve Paralysis:• Upper motor neuron lesion: Only the lower half of the face on the opposite side of the lesion is
affected (the upper half of facial nucleus receives cortico-nuclear fibers from both pyramidal tracts, while
the lower half of the nucleus receives cortico-nuclear fibers from the opposite pyramidal tract only)
•Lower motor neuron lesion: affects the corresponding half of the faceSigns and symptoms of facial nerve paralysis:A. Lesion below the stylomastoid foramen:• Skin creases disappear, with no expressions on the affected side of the face• Inability to close the eyelids (paralysis of orbicularis oculi) or wrinkle the forehead (paralysis of occipito-
frontalis)• Dropped angle of the mouth• Falling of food into the vestibule of the mouth (paralysis of buccinator)
B. Lesion in the facial canal:• All the above, in addition to:• Loss of taste on the anterior part of the tonge on the affected side (due to involvement of chorda tympani)• Decreased salivation, dryness of the mouth (involvement of chorda tympani)• Hyperacusis (involvement of nerve to stapedius)
C. Lesion in the internal acoustic meatus:• All the above, in addition to:• Deafness (due to involvement of the vestibulo-cochlear nerve)
Internal Ear (Labyrinth)The internal ear is formed of:•Bony labyrinth: intercommunicating bony cavities inside the petrous bone•Membranous labyrinth: intercommunicating membranous sacs and ducts inside the bony labyrinth.
Bony labyrinth: formed of three parts; vestibule, semicircular canals and cochlea
The vestibule:• A small ovoid cavity medial to the
tympanic cavity, in front of the semicircular canals and behind the cochlea
• Its lateral wall presents an oval opening; the vestibular (oval) window
• Its medial wall presents an opening for the vestibular aqueduct and perforations for the vestibular and cochlear nerve fibers
• Posteriorly, the vestibule receives the openings of the semicircular canals (5 openings)
• Anteriorly, it communicates with the scala vestibuli of the cochlea
Semicircular canalsvestibule
cochleaVestibular window
Round window
Perforationsfor vestibular n
Perforations for cochlear n
Opening for vestibular aqueduct
Semicircular canals• Three curved canals connected to the posterior part of the vestibule by five openings• According to their position, they are called: superior, posterior and lateral semicircular canals• The three canals are oriented at 90 degrees to one another.• Each canal presents a dilatation at one end forming the ampulla of the semicircular canal
Superior semicircular canal
lateral semicircular canal
posterior semicircular canal
ampullae
cochlea
Round window
Oval window
vestibule
Cochlea• A conical bony cavity resembling a snail shell,
in front of the vestibule• The cochlea is in the form of a bony spiral that
makes 2 ½ turns around a central bony axis (the modiolus)
• The first turn of the cochlea produces a bulge in the medial wall of the tympanic cavity (promontory)
• The modiolus projects into the spiral cochlea with a shelf of bone called the spiral lamina
• Blood veseels and the spiral ganglia pass through the spiral lamina
• The dendritic processes of the spiral ganglion cells perforate the spiral lamina to reach the hair cells
• The axons of the spiral ganglion cells run through the modiolus forming the cochlear nerve which leaves the cochlea through the internal acoustic meatus
Round window
Basal turn of cochlea (promontory)
Bony wall of cochlea
modiolus
Spiral ganglion
Spiral lamina
Cochlear nerve
Membranous labyrinth• The membranous labyrinth (in the form of sacs and ducts) is
enclosed within the bony labyrinth• It is filled with endolymph and bathed in the perilymph of the
bony labyrinth• The membranous labyrinth is composed of:
•Utricle and saccule (enclosed within the bony vestibule)•Semcircular ducts (within the semicircular canals)•Cochlear duct (within the cochlea)•Endolymphatic duct
Utricle:• A small sac in the bony vestibule• It receives the openings of the semicircular ducts• It contains a highly specialized organ for
equilibruim (macula utriculi)• The utricle is connected to the saccule by the
utriculo-saccular duct
Saccule:• A small sac in the bony vestibule• Carries a sensory organ for equilibrium
called the macula sacculiutricle
sacculeUtriculo-saccular duct
Cochlear duct
Semicircular ducts
ampullae Endolympatic duct & sac
Semicircular ducts:• Three ducts which occupy the semicircular canals• They have similar names to the enclosing bony canals• Each duct presents a dilatation (ampulla) enclosed within the corresponding bony ampulla• Each ampulla contains a sensory organ for equilibrium called the crista ampullaris
Endolymphatic duct and sac• Arises from the utriculo-saccular duct• Passes through the aqueduct of the vestibule
to end in a dilatation (endolymphatic sac)• The endolymphatic sac lies under the dura
on the posterior surface of petrous bone
Cochlear duct• Enclosed within the bony cochlea• Contains the sensory organ of hearing (organ
of Corti)• The duct is triangular in cross section• Its floor is formed by an elastic membrane
(basilar membrane)• Its roof is formed by a delicate membrane (the
vestibular membrane)• The organ of Corti lies on the upper surface of
the basilar membrane)• The outer wall of the cochlear duct is adherent
to the bony cochlea and called stria vascularis• The cochlear duct is connected to the saccule
by the ductus reuniens• The space between the vestibular membrane
and bony cochlea is called the scala vestibuli and is continuous with the vestibule
• The space between the basilar membrane and bony cochlea is called the scala tympani
• The scala tympani presents the round window at its lower end
• The two scalae are continuous at the apex of the cochlea through an opening (the helicotrema)
Scala vestibuli
Scala tympani
Spiral lamina
Vestibular membrane
Cochlear duct
Stria vascularis
Bony cochlea
Organ of CortiSpiral ganglion
Cochlear nerve
Basilar membrane
Scala vestibuli
Scala tympani
Round window
Mechanism of hearing:• Sound vibrations collected by the auricle lead to vibrations in the tympanic membrane• These vibrations are transmitted through the auditory ossicles to the base of stapes and augmented about
20 times (due to the small surface area of the base of stapes)• The waves are then transmitted into the vestibular perilymph through the oval window• The perilymph carries the waves into the scala vestibuli where they lead to vibrations of the vestibular
membrane• The vibrations are transmitted into the endolymph of the cochlear duct resulting in vibrations of the
basilar membrane leading to stimulation of the hair cells in the organ of Corti• In the organ of Corti, the vibrations are converted into nerve impulses which are carried by the peripheral
processes of the sprial ganglion cells into the spiral ganglia and cochlear nerve
• The sound vibrations in the perilymph of scala vestibuli are also carried (through the helicometra) to the scala tympani, and continue down to the lower end of the scala tympani where they are eliminated by outward bulging of the secondary tympanic membrane (which closes the round window)
Arterial supply of the labyrinth:•Labyrinthine artery: from the basilar artery•Stylomastoid artery: from the posterior auricular (or occipital a)
Venous drainage:•Into the superior petrosal and transverse sinuses