Anatomy of the Ear

1. ANATOMY OF THE
EAR
BY
DR. A.A. ABIODUN

2. IT IS MADE UP OF THREE REGIONS
 EXTERNAL EAR
 PINNA OR AURICLE
 EXTERNAL AUDITORY CANAL
 MIDDLE EAR
 TYMPANIC MEMBRANE
 MALLEUS, INCUS AND STAPES
 EAUSTATIAN TUBE OR PHARYNGOTYMPANIC TUBE

3. INNER EAR
 BONY AND MEMBRANEOUS LABRYNTH
 VESTIBULE
 SEMI-CIRCULAR CANALS
 COCHLEA
 VESTIBULAR NERVE
 AUDITORY NERVE

4.  MASTOID BONE
 HONEYCOMB OF AIR CELLS
 LOCATED BEHIND, ABOVE AND BELOW THE EAR
 CELLS LINED BY THIN MUCOUS MEMBRANE

5. OUTER EAR
 THE PINNA OR AURICLE
 CONSISTS OF CARTILAGE AND SKIN
 ACTS AS A CHANNEL FOR SOUND WAVES AND DIRECTS THEM TOWARDS THE
EXTERNAL AUDITORY MEATUS AND ON TO THE TYMPANIC MEMBRANE
 MADE UP OF 8 DISTINCT STRUCTURES

6. OUTER EAR CONT’D
 PINNA OR AURICLE
 CARTILAGE COVERED WITH PERICHONDRIUM BOUND TO THE SKIN
 AUDITORY MEATUS
 2/3 CARTILAGE
 1/3 BONE
 STOPS AT THE TYMPANIC MEMBRANE

7.  AUDITORY MEATUS
 CERUMEN (WAX) IS PRODUCED IN THE OUTER 2/3 AND ITS
BACTERICIDAL WHICH AIDS IN THE CLEANING MECHANISM ALONG
WITH EPITHELIAL MIGRATION

8. THE MIDDLE EAR
 THE TYMPANIC MEMBRANE
 ROUGHLY CIRCULAR
 ALMOST TRANSPARANT WITH A CAPILLIARY BLOOD SUPPLY
 JOINS MEATUS AROUND ITS CIRCUMFERENCE (ANNULAR)

9. THE MIDDLE EAR CONT’D
 THE TYMPANIC MEMBRANE
 CONSISTS OF THREE LAYERS
 OUTER EPITHELIAL
 MIDDLE ELASTIC FIBRE
 INNER MUCOUS MEMBRANE

10. THE MIDDLE EAR CONT’D
 THE OSSICLES
 STAPES
 INCUS
 MALLEUS
 TRANFERS SOUND VIBRATIONS FROM THE TYPANIC MEMBRANE TO
THE INNER EAR

11. The malleus
Manubrium
Neck
Head
Lateral process

12. The malleus

13. The incus
Short process
Long process
Lenticular process
Incudostapedial
joint

14. The incus

15. The stapes
Head
Neck
Anterior crus
Posterior crus
Footplate

16. The stapes

17. Articulated ossicular chain

18. EUSTACHIAN TUBE OR PHARYNGOTYMPANIC TUBE
 LINKS THE MIDDLE EAR TO THE PHARYNX
 ALLOWS PRESSURE TO EQUALISE BETWEEN THE ATMOSPHERE AND THE MIDDLE
EAR
 ALLOWS MUCOUS DRAINAGE

19. INNER EAR
 BONY LABRYNTH
 ANTERIORLY THE COCHLEA
 MIDDLE THE VESTIBULE
 POSTERIORLY THE 3 SEMI-CIRCULAR CANALS

20. INNER EAR CONT’D
 VESTIBULE
 THE FLUID FILLED (PERI-LYMPH AND ENDO-LYMPH) CENTRAL CAVITY OF THE BONY
LABYRNTH

21. INNER EAR CONT’D
 SEMI-CIRCULAR CANALS
 RESPONSIBLE FOR SENSING MOTION AND BALANCE
 HOLLOW BONEY TUBES FILLED WITH PERILYMPH
 CONTAINS THE MEMBRANEOUS LABYRNTH AND ENDOLYMPH

22. INNER EAR CONT’D
 THE COCHLEA
A SPIRAL SHAPED FLUID FILLED STRUCTURE LINED
WITH TINY HAIRS (CILLIA) WHICH MOVE WHEN
VIBRATED AND CAUSE A NERVE IMPULSE TO FORM

23. INNER EAR CONT’D
 THE COCHLEA
CONTAINS THE ORGAN OF CORTI THROUGH WHICH
ELECTRICAL (SOUND) IMPULSES ARE SENT ALONG THE
AUDITORY NERVE TO THE BRAIN

24.  THE AUDITORY NERVE
 CARRIES SOUND IMPULSES FROM THE COCHLEA TO THE BRAIN
 THE VESTIBULAR NERVE
 CARRIES BALANCE SIGNALS FROM THE SEMI-CIRCULAR CANALS TO
THE BRAIN

25. Events involved in the creation of an
Auditory action impulse
1. Pinna directs sound waves
 into the external auditory
 meatus.
2. Sound waves cause the
 tympanic membrane to
 vibrate.
 a. Slowly for low-
 frequency sounds
 b. Rapidly for high-
 frequency sounds
 c. Distance the membrane
 travels during these
 vibrations relates to
 loudness or decibels.

26. Events involved in the creation of an
Auditory action impulse
3. Vibrations are communicated
 from the tympanic membrane
 to the auditory ossicles.
 Malleus Incus Stapes
4. Stapes vibrates back and forth
 in the oval window, thus
 vibrating the oval window
 membrane.
5. Vibration of oval window
 membrane causes fluid pressure
 waves in the perilymph of the
 scala vestibuli.

27. Events involved in the creation of an
Auditory action impulse
6. Perilymph pressure waves
 are transmitted to the scala
 tympani and eventually to the round window causing the secondary tympanic membrane to bulge
outward.
7. Vibrations of the vestibular
 membrane cause vibrations
 of the endolymph within the cochlear duct.
8. Endolymph pressure waves
 cause the basilar membrane
 to vibrate.

28. Events involved in the creation of an
Auditory action impulse
 8a. Vibrations of the basilar membrane cause the the hair cells of the Organ of Corti to
vibrate.
 8b. Hair cells vibrate upward, bending the stereocilia against the tectorial membrane.
 8c. Bending the stereocilia produces a receptor potential that ultimately leads to a action
potential on Cochlear nerve.

29. Auditory Pathway
1. First-order neurons in the Cochlear branch of the
Vestibulocochlear nerve
2. Cochlear nuclei in the medulla
3. Superior Olivary nuclei in the medulla
4. Inferior colliculus
5. Medial geniculate nuclei of the thalamus
6. Primary auditory area of the superior temporal gyrus

30. Thanks