Middle Ear

Question 1

How does the middle ear act as an electrical transformer?

Answer 1

Matches the low impedance of air to high impedance of the cochlear fluids

Question 2

How does the middle ear match the low impedance of the air to the high impedance cochlear fluids?

Answer 2

1) Area at eardrum 14x than at footplate stapes
- so pressure at oval window x14 than at drum
2) Ossicular chain acts as a pivotal crank which introduces a lever ratio to motion
- force at stapes is 1.3x that at drum

Question 3

What is the transformer ratio of the middle ear?

Answer 3

18.2

Question 4

Which middle ear muscles reduce the efficiency of sound transmission through the middle ear?

Answer 4

Tensor tympani

Stapedius

Question 5

What is the result of tensor tympani contracting?

Answer 5

Eardrum stiffened, so moves less at a given pressire

Question 6

How can we distinguish between conductive deafness and unilateral sensorineural losses?

Answer 6

Weber’s test

Question 7

What is the Weber test?

Answer 7

Simple expedient of placing a vibrating tuning fork on the vertex if the skull

Question 8

What is the action of the eustachian tube when scuba diving?

Answer 8

Equalising pressure between the atm and the middle ear

Question 9

Result of Weber’s test for unilateral sensorineural losses?

Answer 9

Hearing lounder unaffected ear

Question 10

What is the result of stapedius contracting?

Answer 10

Pulls on side of stapes to alter the angle at which the footplate plunges into the oval window

Question 11

What is the action of tensor tympani and stapedius at sound Ps above 80 dB SPL?

Answer 11

Reflex contraction