1.
Mechanism Of Hearing
Anirudha K

2.
Sound
• Waves of Compression and Rarefaction

3.
• Mechanical conduction
– Conductive apparatus
• Transduction of mechanical energy to electrical
energy
– Sensory system of Cochlea
• Conduction of Electrical Impulses to the brain
– Neural pathway

4.
Conduction…
♦External Ear (Pinna)
– Collects the sound
– Funnel shape
– Localisation of Sound
♦External Auditory Canal
– Directs the sound waves
♦Reaches the Tympanic Membrane

5.
Middle Ear
• Impedence Matching
1. Lever action of Ossicles
2. Hydraulic action of Tympanic membrane
3. Curve of Tympanic membrane
4. Phase difference Maintainance
5. Natural resonance of External and Middle
ear

6.
1.Lever Action of Ossicles
Length of Long process of malleus
Length of Long process of Incus
1.3=

7.
2.Hydraulic action of TM
Area of Tympanic Membrane
Area of Footplate of Stapes
55 sq.mm
3.2 sq.mm
17.1
Total Transformer Ratio
= 17.1 × 1.3
= 22.1

8.
3. Curve of the Tympanic membrane
• Movements of the tympanic membrane are
more at the periphery than at the centre
where the handle of malleus is attached.

9.
Phase difference between Round and
Oval Windows
• If no tympanic membrane was present, the
sound would have struck both the Round and
oval Window simultaneously, thus cancelling the
vibrations produced since they are two ends of a
continuous channel.
• Ossicular chain – Preferential Path to Oval
Window…
• So when Oval window is in compression, Round
window is in Rarefaction ,and Vice Versa…

10.
Natural Resonance of External and
Midlde Ear
• Natural Resonance of
– External Ear canal : 3000Hz
– Tympanic Membrane :800-1600Hz
– Middle ear : 800Hz
– Ossicular Chain : 500-2000Hz
Greatest Sensitivity of Sound transmission is
between : 500Hz – 3000Hz
Which is fortunately the frequencies most important to
humans in day-to-day life…

11.
Transduction of Mechanical energy to
Electrical Energy
Movement of
Stapes Footplate Oval Window
Movement of
Cochlear Fluid :
Perilymph
Movement of
Basillar
membrane
Movement of
Organ of Corti
Shearing force
between Tectorial
Membrane and Hair
Cells
Distorsion
of Hair cells
Cochlear
Microphonics
Nerve
Impulse

12.
Neural Pathway

13.
ThanQ…