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1. MECHANISM OF HEARING
&
AUDITORY PATHWAY
PBL 2

2. OBJECTIVES
• Hearing mechanism
• Auditory pathway
• Deafness

3. EXTERNAL EAR
Pinna and Concha
• Gather sound energy
• provides cue about the elevation of sound source (due to selective
frequency)
Auditory meatus
• Boost the sound pressure (30 -100 times) for 3KHz frequency – resonance
effect
( makes sensitive to hearing loss in 2-5KHz – explosion , heavy machinery
sound)

4. MIDDLE EAR
• Amplification by ear ossicles
By two mechanical process
1. by focusing the force from
large area to small area
2. mechanical advantage gained
by lever action of ossicles
Tensor tympani (CN V) and
Stapedius (CN VII) – protect inner ear

5. INNER EAR
(MECHANO-ELECTRICAL TRANSDUCTION )

7. Basilar membrane
• Base - Thick and narrow – high
frequency
• Apex- Thin and wider – Low

8. Stria vascularis –
increases endolymph conc.
K+

10. Shearing force bend the stereocilia

12. Mechano-electrical
transduction
# Kinocilium disappear
after birth
# Movement toward
longest stereocilium -
Depolarization
Endolymph
Rich in K+
Perilymph
As Normal ECF

15. DEAFNESS
Unilateral hearing loss – Peripheral hearing apparatus damage
Bilateral hearing loss – Central lesion in auditory pathway
Conductive deafness : impaired sound transmission ( External
and middle ear)
Sensorineural deafness : loss of cochlear hair cell / cochlear
nerve damage

16. REFERENCES
1. Neuroscience, purves et. Al , 5e
2. medical physiology, Guyton and hall
3. Costanzo medical physiology

17. •Thank you