The document discusses the anatomy and physiology of the peripheral and central auditory system. It describes the three main parts of the ear - the outer, middle, and inner ear. The outer ear includes the pinna and external auditory canal. The middle ear contains the tympanic membrane, ossicles, and auditory tube. It functions to couple sound energy to the cochlea in the inner ear and provide physical protection. The inner ear houses the cochlea for sound transduction and the vestibular system for balance.

1. Anatomy and physiology of the
peripheral and central auditory
system
Lecture 2(a)
Dr. Ghulam Saqulain
M.B.B.S., D.L.O, F.C.P.S
Head of Department of E.N.T
Capital Hospital

5. Sound:
 Sounds travels at 344 m/ s
 When sound passes from air to liquid 99.9% is
reflected.

7. Ear comprises of three main parts
playing their own vital role:
Outer Ear Middle Ear Inner Ear.

9. EXTERNAL
EAR
MIDDLE EAR
INTERNAL EAR

10. OUTER EAR
 Pinna and External Auditory Canal
 Pinna:
 elastic cartilage
 muscles
 thin skin.

11. External auditory Canal
 Curved tube
 Covered by skin
 S shaped in adult
 Inner2/3-bone
 outer1/3-cartilage..
 ceruminous gland
in outer 1/3

13. Function:

14.  EAC Channel the auditory stimuli along the
meatus to the tympanic membrane
 Gain in sound pressure at T.M Pinna-concha
system 15-20 db
 Sound Localization
 Monoaural
 Binaural

15.  Thin fibrous membrane
 Obliquely set
 facing d/w,f/w & lat.
 Divides Ext.ear
fr. Middle ear
 note;
 Medial surface
 handle of Malleus ..
Ear drum/ Tympanic
Membrane

16. Sensory nerve supply
 1.Great auricular
 -Cranial aricular surface
 2.Auriculo temporal
 -lateral surface of auricle
 -ext.audit.meatus
 -ext.surf. tympan.memb.
 3.Auricular br. of Vagus
- floor xt.aud.meatus&
 adjoin.tympanic memb.

17. Appearance of Tympanic membrane
under otoscopic examination
 Tymp.membrane.is concave
laterally
 Umbo -depression at the
deepest part produced by tip
of handle of Malleus
 Cone of light is produced at antero
inferior quadrant of membr,
 *Not visible in middle ear
infections .
Umbo
Cone of light

18. Tympanic membrane
(in Otoscopic examination)
 Depression at depth of
concavity
??
On illumination ?
?

19. MIDDLE EAR
 It is an AIR filled space. Part of the ear
between the tympanic membrane and
the oval window
 Contents:
 Air
 Ossicles: Malleus, Incus and
Stapes
 Muscles: Tensor tympani,
Stapedius
 The TYMPANIC MEMBRANE (ear
drum) vibrates in response to sound.
 Attached to it are 3 bones: The
MALLEUS (hammer), INCUS (anvil),
and the STAPES (stirrup) are the
smallest bones in the body.
 Their function is to amplify sound
vibrations. The malleus vibrates the
incus, which vibrates the stapes.

20.  The middle ear is open to the
nasopharynx by way of the
AUDITORY TUBE
 If this tube is closed, the ears
feel plugged up.
 The function of the auditory
tube is to equalize the
pressure of the middle ear
and the outside air so the ear
bones can vibrate.
 3 Ossicles
 2 Muscles
 Tensor tympani
 Stapedius
 3 Nerves
 Chorda tympani
 Tympanic plexus
 Lesser petrosal
Main Contents:

23. Walls & boundaries
of Middle ear:
 It hasIt has
 RoofRoof
 FloorFloor
 Anterior wallAnterior wall
 Post. wallPost. wall
 Lat. WallLat. Wall ..
 Medial wallMedial wall

24. Roof,Floor & their relations:
 RoofRoof
 Tegmen tympaniTegmen tympani
 Petrous temporalPetrous temporal
 --Temporal lobeTemporal lobe
 FloorFloor
 Thin plate of boneThin plate of bone
 Internal jugular veinInternal jugular vein....

25. Anterior Wall
 Ant.WallAnt.Wall
 Two openingsTwo openings
-- canal -Tensor tympanicanal -Tensor tympani
--Auditory tubeAuditory tube
Thin plate separatingThin plate separating
--Internal CarotidInternal Carotid
arteryartery
Tensor tympani Audit.tube

26. Post.Wall:
. .
 Large opening
-Aditus Mastoid antrum
 Small projection
Pyramid
-Stapedius
Note;
Facial nerve bends d/w.on the medial
side of aditus, descends b/h. Pyramid
& emerges thro’Stylomastoid foramen

27. Lateral wall:
 Lat.wall
-Tympanic membrane
-Epitympanic recess
Tympanic
membrane

28. Medial Wall:
 Rounded projection
*Promotory ?
1st
.turn of Cochlea
*tympanic plexus (ix)
 Two openings
*Fenestra vestibuli (oval)
Stapes - - -Separating
fr.perilymph of internal ear
*F.Cochleae (round)
-2nd
.tym.membr.
 -VII.N. . Bends sharply b/w. over
Promonory & reaches post wall promontory
F.Vestibuli
•lat.semicircular canallat.semicircular canal ..

29.  Functions:
 It couples sound energy to the cochlea
 Physical protection of cochlea
 Matches the impedance of air --cochlear fluids
 Apply sound preferentially to one window
 Impedance Transformer Mechanism
Low pressure High Displacement – High pressure Low Displacement

30.  This occurs as follows:
 Liver action of ossicles: 1.3:1
 Mechanical advantage 1.3
 Hydraulic Action of T.M 14:1
 Curved Membrane effect
 Natural Resonance of Ext. and Middle ear

32. Physical Protection of Cochlea: