1. ANATOMY AND PHYSIOLOGY OF THE EAR
Yard.Doc.Dr.Müzeyyen Doğan

2. Learning goal and objectives of the lesson
Learning goal of the lesson: The learner should know the basic anatomic structures and physiology of external, middle and inner ear
Learning objectives of the lesson the learner will be able to:
identify the anatomic structures of the external, middle and inner ear
identify the physiology of the external, middle and inner ear
identify the physiology of the hearing
identify the physiology of the balance
Skill objectives the learner will be able to ear examination

5. OUTER EAR Consists of the auricle and EAM Skin-lined apparatus
Approximately 2.5 cm in length
Ends at tympanic membrane

6. OUTER EAR Auricle is mostly skin-lined cartilage
External auditory meatus
Cartilage: ~40%
Bony: ~60%
S-shaped
Narrowest portion at bony-cartilage junction

7. Anatomy and Physiology
EAC is related to various contiguous structures
Tympanic membrane
Mastoid
Glenoid fossa
Cranial fossa
Infratemporal fossa

8. Anatomy and Physiology
Squamous epithelium
Bony skin – 0.2mm
Cartilage skin
0.5 to 1.0 mm
Apopilosebaceous unit

9. The Middle Ear: A cleft within the temporal bone
Lining is mucous membrane
Tympanic Membrane separates it from EAC
Eustachian tube connects it to nasopharynx
Also Connected to Mastoid Air Cells

10. Middle Ear Structures 1- Malleus 2- Incus --Ossicles 3- Stapes
4- Tympanic Membrane (Eardrum)
5- Round Window
6- Eustachian Tube

11. Middle Ear Muscles
1. The Stapedius Attaches to Stapes,Contracts in Response to Loud sounds, chewing, speaking; Facial (VIIth cranial) nerve
2. The Tensor Tympani Helps open Eustachian tube

14. 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

15. Middle Ear Functions
Impedance Matching
Filtering
Acoustic Reflex

16. Impedance Matching
The middle ear allows the impedance matching of sound traveling in air to acoustic waves traveling in a system of fluids and membranes in the inner ear

17. Acoustic Reflex
The movement of the ossicles may be stiffened by two muscles, the stapedius and tensor tympani, which are under the control of the facial nerve and trigeminal nerve, respectively. These muscles contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the acoustic reflex

18. Middle Ear Transmits Energy by Two Pathways:

19. MECHANISMS OF MIDDLE-EAR GAIN
Acoustic Coupling
Ossicular Coupling
Area Difference (TM to footplate)
Lever Action (Malleus to Incus)

20. Acoustic Coupling
The collected pressure of sound vibration that strikes the tympanic membrane is therefore concentrated down to this much smaller area of the footplate, increasing the force but reducing the velocity and displacement, and thereby coupling the acoustic energy.

21. Anatomy and Physiology
Ossicular Amplifier System

22. MIDDLE-EAR GAIN
The ossicles are classically supposed to mechanically convert the vibrations of the eardrum, into amplified pressure waves in the fluid of the cochlea (or inner ear) with a lever arm factor of 1.3. Since the area of the eardrum is about 17 fold larger than that of the oval window, the sound pressure is concentrated, leading to a pressure gain of at least 22.

23. 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)

24. Ear

25. INNER EAR INNER EAR : Cochlea – hearing Vestibule – static equilibrium
Semicircular canals – dynamic equilibrium

35. OHC vs. IHC Function Vestibulocochlear nerve – cranial nerve VIII
Audible range: ,000 hertz
Ossicles amplify sound 22 X
Some nerve fibers cross over to opposite side of brain

36. Hair Cells
Outer Hair Cells
Inner Hair Cells
OHC movie

37. OCH Cilia Theory: Tip-links
<<<IHC
OHC >>>

38. Equilibrium – Balance
Static equilibrium – maintenance of body posture relative to gravity while the body is still.
Dynamic equilibrium – maintenance of the body posture (mainly the head) in response to sudden movements. Tracking a moving object.

39. Static Equilibrium Inside the vestibule are two chambers :
utricle and saccule.
Regions of hair cells and supporting cells called maculae.
Otoliths – “ear rocks”

43. Dynamic Equilibrium Semicircular canals
In ampulla is the crista ampullaris – contains hair cells and supporting cells covered by a gelatinous mass called the cupula.
Neurological connections between eyes and semicircular canals – for tracking
Nystagmus