Mechanism Of HearingAnirudha K

Sound• Waves of Compression and Rarefaction

• Mechanical conduction– Conductive apparatus

• Transduction of mechanical energy to electrical energy– Sensory system of Cochlea

• Conduction of Electrical Impulses to the brain– Neural pathway

Conduction…

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

Middle Ear

• Impedence Matching

1. Lever action of Ossicles2. Hydraulic action of Tympanic

membrane3. Curve of Tympanic membrane4. Phase difference Maintainance5. Natural resonance of External and

Middle ear

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

2.Hydraulic action of TMArea of Tympanic MembraneArea of Footplate of Stapes

55 sq.mm3.2 sq.mm

17.1

Total Transformer Ratio = 17.1 × 1.3 = 22.1

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.

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…

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…

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 Microphonic

s

Nerve Impulse

Neural Pathway

ThanQ…