1. M.Rogha M.D Isfahan university of medical sciences
Anatomy of the Ear
M.Rogha M.D
Isfahan university of medical sciences

2. Major Divisions of the Ear
Peripheral Mechanism
Central Mechanism
Outer Ear
Middle Ear
Inner Ear
VIII Cranial Nerve
Brain

3. External ear, Auris externa
Auricula
Meatus acusticus externus
Middle ear, Auris media
Cavitas tympani
Membrana tympanica
Ossicula auditus
Tuba auditiva
Inner ear, Auris interna
Labyrinthus membranaceus
- Labyrinthus vestibularis
- Labyrinthus cochlearis
Labyrinthus osseus
- Vestibulum
- Canales semicirculares ossei
- Cochlea
- Meatus acusticus internus

4. Pinna External Auditory Meatus Outer Ear Pinna Preauricular Tags
Preauricular Pits
EAM
Cerumen
Pinna
External
Auditory
Meatus
Function
EAM resonance

5. Function of Outer Ear
Collects sound
Localization
Resonator
Protection

6. Pinna The visible portion that is commonly referred to as "the ear"
Helps localize sound sources
Directs sound into the ear
Each individual's pinna creates a distinctive imprint on the acoustic wave traveling into the auditory canal

7. External Auditory Meatus
Extends from the pinna to the tympanic membrane
About 26 mm in length and 7 mm in diameter in adult ear.
Size and shape vary among individuals.
Protects the eardrum
Resonator
Provides about 10 decibels (dB) of gain to the eardrum at around 3,300 Hertz (Hz).
The net effect of the head, pinna, and ear canal is that sounds in the 2,000 to 4,000 Hz region are amplified by 10 to 15 dB.
Sensitivity to sounds greatest in this frequency region
Noises in this range are the most hazardous to hearing

8. Outer ear
Tissues: elastic cartilage covered with skin A. Meatus acusticus externus besides the hair follicles and fat glands contains: Glandulae ceruminosae – modified sweat glands on the lateral wall of the canal. Сerumеn (ear wax) combination of wax and fat glands secret and desquamated epithelial cells.

9. Middle Ear
Tympanic Cavity
Tympanic Membrane
Ossicles
Middle Ear Muscles
Eustachian Tube
Mastoid

10. Function of Middle Ear Conduction Protection Transducer Amplifier
Conduct sound from the outer ear to the inner ear
Protection
Creates a barrier that protects the middle and inner areas from foreign objects
Middle ear muscles may provide protection from loud sounds
Transducer
Converts acoustic energy to mechanical energy
Converts mechanical energy to hydraulic energy
Amplifier
Transformer action of the middle ear
only about 1/1000 of the acoustic energy in air would be transmitted to the inner-ear fluids (about 30 dB hearing loss)

11. Tympanic cavity Volume – 1.5 ml Form – flatten drum
Structure – six walls:
- Lateral
- Medial
- Anterior
- Posterior
- Superior
- Inferior

12. Lateral wall

13. Tympanic Membrane Separates outer ear from middle ear
Barrier from foreign objects
Cone-shaped in appearance
about 17.5 mm in diameter
Vibrates in response to sound waves.
The membrane movement is incredibly small
as little as one-billionth of a centimeter

14. Tympanic membrane Two parts: Pars flaccida – upper, thin, loose
Pars tensa – lower, tense
Three layers:
1. Outer, cutaneous – continuation of the canal skin. No hairs and glands.
2. Middle, fibrous – elastic fibers.
3. Inner, mucous – tympanic cavity lining

15. Medial wall, paries labyrinthicus
Most complex.
On this wall are distinguished:
-fenestra vestibuli
-fenestra cochleae
-promontorium
-prominentia canalis semicircularis lateralis
- prominentia canalis facialis
Superior wall, paries tegmentalis
Separates tympanic from cranial cavity.
Children less than 2 years – infections of the middle ear can pass to the cranial cavity.

16. Inferior wall, paries jugularis
Separates tympanic cavity from fossa jugularis
Anterior wall, paries caroticus
Separates tympanic cavity from canalis caroticus
canalis musculotubularis
Posterior wall, paries mastoideus
Composed of:
Styloid complex of Procter
Antrum mastoideum
Fossa incudis

17. Auditory (Eustachian) tube
Connects tympanic cavity with pharynx
Two openings:
ostium pharyngeum tubae
ostium tympanicum tubae.
Two parts:
bony
cartilagenous
Function:
Equalizes pressure on both sides of tympanic membrane for optimal hearing.

18. Ossicles Malleus (hammer) Incus (anvil)
Stapes (stirrup) smallest bone of the body

19. Inner Ear Auditory Vestibular Vestibular Cochlear semicircular canals
utricle and saccule
Cochlear
traveling wave
pathologies
Auditory
Vestibular

20. Inner ear Two compartments: (а) Bony labyrinth and
(b) Membraneous labyrinth.
Bony labyrinth:
 complex cavity in dense bone (pars petrosa)
Parts of the bony labyrinth:
a.Vestibulum.
b. Semicircular canals.
c.Cochlea.

21. Vestibulum and semicircular canals
Bony labyrinth.
Labyrinthus osseus
Vestibulum and semicircular canals

22. Vestibulum Two walls: External and internal. External wall has
Fenestra vestibuli.
Internal wall has:
Recessus ellipticus
Recessus sphericus
Recessus cochlearis
Maculae cribrosae superior, medius, inferior

23. Openings into vestibulum
a. Fenestra vestibuli. b. Fenestra cochleae. c. Openings (5) of the semicircular canals d. Aqueductus vestibuli

24. Semicircular canals 3: anterior, posterior and lateral.
Have ampulla and crus.
Canalis semicircularis lateralis –horizontal.
- eminentia canalis semicircularis lateralis on the medial wall of
tympanic cavity.
Canalis semicircularis anterior –frontal.
- eminentia arcuata on pars petrosa of os temporale.
Canalis semicircularis posterior –sagittal

25. Labyrinthus osseus. Cochlea Meatus acusticus internus

26. Cochlea Cone-shaped: base and apex. Canalis spiralis cochleae
- promontorium, on the medial wall of tympanic cavity.
Modiolus
- canales longitudinales modioli.
Lamina spiralis ossea
hamulus
Divides canalis spiralis cochleae into:
Scala tympani
Scala vestibuli

27. Labyrinthus membranaceus

28. Function of Inner Ear
Converts mechanical sound waves to neural impulses that can be recognized by the brain for:
Hearing
Balance

29. Membraneous labyrinth. Labyrinthus membranaceus
Closed system of sacs and ducts underling the bony labyrinth.
Filled with endolymph.
Two parts:
vestibular & cochlear.

30. Vestibular labyrinth Composed of : Two bags - sacculus et utriculus
Three ductus semicirculares
One ductus endolymphaticus.

31. Cristra ampullaris

32. Balance
Linear motion
Rotary motion

33. Sensory cells (Epitheliocytus pilosus)

34. Macula utriculi (sacculi)
Otoliths. Statoconia

35. Static balance
Maculae react to gravitational forces and participate in maintaining the static balance.

36. Dynamic balance
Cristae ampullares react to rotatory movements and paticipate in dynamic balance.

37. Cochlea
The cochlea resembles a snail shell and spirals for about 2 3/4 turns around a bony column
Within the cochlea are three canals:
Scala Vestibuli
Scala Tympani
Scala Media

38. Cochlear labyrinth Spiral canal - ductus cochlearis.
Occupies scala media of the spiral canal.
Has two blind ends - cecum vestibulare and cecum cupulare.
Has three walls:
paries vestibularis
paries externus
paries tympanicus- organ of Corti, basal membrane

39. Organ of Corti
End organ of hearing

40. Organ of Corti

41. Sensory cells of the organ of Corti