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What is Surface area of tympanic membrane (ear drum)? and explain in detail?
Ans. D. 90 mm2. (Ref: PL Dhingra 5th/pg. 18). The tympanic membrane has a cross-sectional area of approximately 90 sq. mm. and the energy falling on that area is concentrated upon an area of 3.2 sq. mm. represented by the stapes. TYMPANIC MEMBRANE # The normal tympanic membrane is pearly/shiny gray color. 6 # It has an oval shape with an average surface area of approximately 90mm2. # The concavity on its lateral surface is more marked. # The normal tympanic membrane is mobile. # It consists of a lax portion, the pars flaccida (sharpell's membrane), and a larger taut portion, the pars tensa, which is drawn inwards at its center to form the umbo. # At the tip of the malleus is the umbo.6 # Some middle ear structures can be seen through a transparent membrane. # Most prominent part of tympanic membrane seen on Otoscopy is the lateral process of the malleus. # Attic area is pinkish and lies above lateral process of the malleus # TM can be divided into 4 quadrants: - anterosuperior - anteroinferior - posterosuperior - posteroinferior # The quadrants of TM are clinically important as they are used in describing the location of lesions. # Cone of light (helpful in evaluating tension of TM ) is seen in the anteroinferior quadrant. # The most common site of Cholesteatoma is Posterosuperior part. # note: AQUINO'S SIGN is the blanching of the tympanic mass with gentle pressure on the carotid artery. The surface area of tympanic membrane = 90 mm2 Effective vibratory area of tympanic area = 45 mm2. Foot plate area = 3.2 mm2 Area ratio = 14:1 Ossicular ratio6 = 1.3: 1 Total transformer ratio = 14 x 1.3: 1-18.2: 1