Anatomy of inner and middle ear

1. Ear
Dr Zaid Azhar

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

3. Major Divisions of the Ear

4. External Ear
• Auricle/Pinna -
elastic cartilage
• External Auditory
Meatus - One
third
cartilaginous, two
thirds bony

5. Tympanic Membrane

6. Tympanic Membrane
• Cone-shaped in appearance
• The eardrum separates the outer
ear from the middle ear
• Creates a barrier that protects the
middle and inner areas from
foreign objects
• The eardrum vibrates in response
to sound pressure waves.
• The membrane movement is
incredibly small as little as one-
billionth of a centimeter

7. Function of Outer Ear
• Collect sound
• Localization
• Resonator
• Protection
• Sensitive (earlobe)

8. Cerumen/ Earwax
The purpose of wax:
• Repel water
• Trap dust, sand particles, micro-
organisms, and other debris
• Moisturize epithelium in ear
canal
• Odor discourages insects
• Antibiotic, antiviral, antifungal
properties
• Cleanse ear canal

9. Outer Ear Care
Hazardous to health:
• Ear candling
• Swabs
• Foreign objects

10. Middle Ear

11. Contents Middle Ear
• Air
• Ossicles
• Tensor tympani
muscle
• Stapedius muscle
• Chorda tympani
nerve
• Facial nerve

12. Function of Middle Ear
• Conduction
– 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)

13. Eustachian Tube

14. Eustachian Tube
• The eustachian tube connects the front wall of the middle
ear with the nasopharynx
• The eustachian tube also operates like a valve, which
opens during swallowing and yawning
• This equalizes the pressure on either side of the eardrum,
which is necessary for optimal hearing.
• Without this function, a difference between the static
pressure in the middle ear and the outside pressure may
develop, causing the eardrum to displace inward or
outward
• This reduces the efficiency of the middle ear and less
acoustic energy will be transmitted to the inner ear.

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

16. Middle Ear Muscles
• Tensor tympani
– Attached to malleus
– Innervated by V, trigeminal nerve
• Stapedius
– Attached to stapes
– Innervated by VII, facial nerve
• Middle Ear Muscle Function:
– Help maintain ossicles in proper position
– Protect inner ear from excessive sound
levels
• When ear exposed to sound levels above
70 dB, the muscles contract, decreasing
amount of energy transferred to inner ear
– This protective reflex termed "acoustic
reflex"

17. Ligaments of Middle Ear
• Function
– restrict and confine
the effect of ossicles
to act as a lever
– restrict movements to
reduce the chance of
damage to the inner
ear
– prevents distortion to
sound

18. Inner Ear

19. Function of Internal Ear
• Convert mechanical sound
waves to neural impulses that
can be recognized by the brain
for:
– Hearing
– Balance

20. Balance
• Linear motion
• Rotary motion

21. 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

22. Cochlea
• 2 ¾ turns
• Axis of internal
acoustic meatus
• Spiral lamina
• Basilar membrane
• Vestibular membrane

23. • Oval window
• Scala vestibuli
• Scala tympani
• Secondary tympanic
membrane
• Contain perilymph
• Scala media or duct of
cochlea contains
endolymph
Cochlea

24. Scala Media
• Basilar membrane
• Spiral organ
• Hair cells of organ of
corti
• Tectorial membrane
• Single row of inner hair
cells
• Each one has 20 large
afferent
• Outer hair cells

25. Sound Waves
• Auricle
• External ear
• Tympanic membrane
• Malleous, incus, stapes
• Oval window
• Pressure waves in scala
vestibuli, scala media, scala
tympani
• Round window

26. Sound Waves

27. Organ of Corti

28. Organ of Corti

29. Afferent Neural Innervations

30. Hair Cells
• Outer Hair
Cells
• Inner Hair
Cells

31. Central Auditory Mechanism
Auditory Path
Virtual Tour of the Ear
Auditory Path

32. Auditory Nerve
• Receptors are hair cells of
organs of corti
• Bipolar cells
• Cell bodies are in the spiral
ganglion on the
• Spiral lamina
• Auditory nerve attached to
lower border of pons
• Cerebellar-pontine angle

33. Auditory Pathway
• First order neurones end
on ventral and dorsal
cochlear nuclei
• On inferior cerebellar
peduncle
• 2nd order neurones
• Trapezoid body
• Lateral leminiscus
• Inferior colliculus
• Superior olivary nucleus

34. • Inferior colliculus
• Via inferior brachium
• Medial geniculate body
• 3rd order neurones
• Auditory radiations to
auditory cortex in temporal
lobe
Auditory Pathway

35. Central Auditory Path

36. Vestibular Apparatus
• Bony labyrinth
• Bony cochlea
• Vestibule
• Bony semi circular canals
• Contain perilymph
• Communicates with CSF
• Subarachnoid space

37. • Membranous labyrinth
• 3 semi-circular canals
• Dilations called utricle
and saccule
Vestibular Apparatus

38. Vestibular Receptors

39. Receptors
• Sensory static receptors in
macula of the utricle and
saccule
• Cristae of the ampullae are the
end organs of the dynamic
movement semi circular canals
• Maculae respond to linear
acceleration of head in
horizontal or vertical plane
during walking

40. • Hair cells are found in the
macula discharge all the time
• Cilia on the hair cells
embedded in gelatinous
substance containing calcium
carbonate crystals
Receptors