1. External acoustic meatus
ANATOMY OF THE EAR
The organ of hearing and equilibrium
Divided into three parts:
External ear
Middle ear
Internal ear
External ear
Includes:
The Auricle and;
The External acoustic meatus
Middle ear
Internal ear
auricle
External acoustic meatus
External ear

2. External Ear
Auricle
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
Superior & inferior
crura of antihelix
Triangular fossa
Helix
Antihelix
Crus of helix
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
Concha
Tragus
Antitragus
Lobule

3. Auricularis posterior External acoustic meatus
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.
Auricularis superior
Auricularis posterior
Auricularis anterior
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
External acoustic meatus

4. 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
External acoustic
meatus
Tympanic membrane
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)

5. Tympanic Membrane anterior view Lateral view
Lateral process
of malleus
Handle of
malleus
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
acoustic meatus
External
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
Posterior malleolar
fold
anterior view
Pars flaccida
Handle of
malleus
Anterior malleolar
fold
Layers of the tympanic membrane:
Outer cuticular layer
Middle fibrous layer
Inner mucous layer
Lateral process
of malleus
Cone of
light
Lateral view

6. 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

7. Summary of arterial & nerve supply of external ear
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
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
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)

8. Posterior
Medial
Lateral
Anterior
A n t e r i o r v i e w

9. Anterior view 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
Tympanic
membrane
Stapes
Epitympanic recess
malleus
External
auditory meatus
External
auditory meatus
Tympanic membrane
Auditory tube
IJV
Auditory tube
Anterior view

10. Medial view 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
Epitympanic recess
Malleus
Incus
Stapes
External acoustic
meatus
Tympanic membrane
Auditory tube
Medial view
Anterior view

11. Walls of the Middle Ear Anterior view 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
Anterior view
IJV

12. Aditus to mastoid antrum
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
Mastoid antrum
Chorda tympani
Aditus to mastoid antrum
Mastoid air cells
Epitympanic recess
Tensor tympani
Auditory tube
ICA
IJV
Facial nerve
ICA
Jugular fossa
Handle of malleus
Medial view

13. Tendon of stapedius muscle
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.
Tegmen tympani
Facial nerve
Mastoid antrum
Tensor tympani
Pyramid
Chorda tympani
Tendon of stapedius muscle
Facial nerve
Auditory tube
Jugular fossa
Lateral View (tympanic membrane removed)

14. Medial view 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)
Epitympanic recess
Anterior canaliculus
for chorda tympani
Tensor
tympani
Chorda tympani
Medial view

15. Lateral view 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.
Tendon of stapedius
pyramid
Oval window closed by base of stapes
Prominence of facial canal
Chorda tympani
Tensor tympani
Lateral view
Auditory tube
Round window
Promontory showing
tympanic plexus of nerves
ICA
Facial nerve

16. Posterior Medial Lateral Anterior Oval window
(closed by base of stapes)
Promontory formed by
the basal turn of cochlea
Auditory tube
Round window closed by
the secondary tympanic membrane
Base of stapes
Prominence of
facial canal

17. Auditory Ossicles Malleus: Medial view
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
Body of incus
Head of malleus
Lateral process
Anterior process
stapes
Handle of malleus
Medial view

18. External acoustic meatus
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 malleus
Body of incus
incus
malleus
External acoustic meatus
stapes
Short limb of incus
Long limb of incus
Tympanic membrane
Head of stapes
Anterior view
Medial view

19. External acoustic meatus
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 & post
limbs of stapes
incus
Neck of stapes
malleus
Base of stapes
External acoustic meatus
stapes
Medial view
Tympanic membrane
Anterior view

20. Auditory Muscles Lateral view Tensor tympani Stapedius
Handle of malleus
Tendon of
tensor tympani
Tensor tympani
O: cartilaginous part of the auditory tube and walls of the canal for tensor tympani
I: handle of malleus
N: mandibular nerve (through a branch from the nerve to medial pterygoid)
External auditory
meatus
Stapedius
O: inner wall of the pyramid
I: neck of stapes
N: facial nerve (the nerve to stapedius arises in the facial canal)
Anterior view
Tendon of stapedius
Pyramid
Neck of stapes
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
Lateral view

21. Mastoid antrum Medial view Relations of the mastoid antrum:
An 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

22. Superior view

23. 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)

24. Facial Nerve Superior view Course Lateral view
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
Prominence
of facial canal
pyramid
Tendon
of stapedius
Vestibular window
Chorda tympani
geniculum
Greater petrosal n
Promontory &
tympanic plexus
Facial nerve
Superior view
Lateral view

25. Medial view Epitympanic recess Chorda tympani Tensor tympani
Facial nerve
Medial view

26. Branches of the Facial Nerve
Communicating 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

27. 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
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

28. Branches of the Facial Nerve

29. 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
Geniculate ganglion
Greater petrosal
Tympanic plexus
Tympanic nerve
Jugular fossa

30. Venous drainage of the middle ear:
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

31. 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 face
Signs 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:
Deafness (due to involvement of the vestibulo-cochlear nerve)

32. Perforations for cochlear n Opening for vestibular aqueduct
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 canals
vestibule
Perforations
for vestibular n
Perforations for cochlear n
cochlea
Vestibular window
Round window
Opening for vestibular aqueduct

33. 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
ampullae
vestibule
lateral semicircular canal
Oval window
cochlea
posterior semicircular canal
Round window

34. Basal turn of cochlea (promontory)
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)
modiolus
Spiral lamina
Bony wall of cochlea
Spiral ganglion
Cochlear nerve

35. Endolympatic duct & sac Utriculo-saccular duct
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
Semicircular ducts
Endolympatic duct & sac
ampullae
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
Cochlear duct
Saccule:
A small sac in the bony vestibule
Carries a sensory organ for equilibrium called the macula sacculi
utricle
Utriculo-saccular duct
saccule

36. Endolymphatic duct and 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

37. 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)
Vestibular membrane
Spiral lamina
Cochlear duct
Stria vascularis
Scala vestibuli
Bony cochlea
Scala tympani
Organ of Corti
Spiral ganglion
Basilar membrane
Cochlear nerve
Scala vestibuli
Scala tympani
Round window

38. Arterial supply of the labyrinth:
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