Tympanic membrane is the partition between external auditory canal & middle ear.
Measurement- * 9-10 mm tall
* 8-9 mm wide
* 0.1 mm thick
* Periphery thickened to form a fibrocartilaginous ring called “Annulas tympanicus”, fits in the tympanic sulcus.
* Central part tented inwards at the level of tip of malleus, called “umbo”.
* Cone of light seen in antero inferior quadrant.
Layers- Three layers-
*** ROLL OF TYMPANIC MEMBRANE IN SOUND TRANSMISSION:
Tympanic membrane helps in mechanical conduction of sound.
A sound signal in the environment
Collected by pinna
Pass through the EAC
Strikes the TM
Vibrations of TM are transmitted to Stapes foot plate through a chain of ossicles coupled to TM.
Conduction is accomplished by-
Effective vibratory area of TM- 40-45 mm2.
Foot plate area 3.2 mm2.
So, Effective area ratio is 14:1.
Lever ratio of ossicles is 1.3:1
So, total transformer ratio is (14*1.3) : 1 ≈ 18:1
This is the mechanical advantage provided by TM.
© 2017 Medshale - All rights reserved