Outer and Middle Ear

Question 1

What are the two main functional purposes of the pinna?

Answer 1

Acts as an acoustical antenna to collect sound

Gain- low frequency filter/resonator tube

Question 2

What are the major audiological consequences of pinna damage?

Answer 2

Mostly aesthetic consequences – i.e. microtia, macrotia, anotia

Question 3

In children, the ear canal is roughly what direction? In adults?

Answer 3

Children - more horizontal

Adults - roughly perpendicular, slight downward

Question 4

What is the general shape of the ear canal? What is it shaped like this?

Answer 4

Ear canal has two turns and is shaped like a lazy s

Protective

Question 5

What portion of the ear canal is surrounded by cartilage? Bone?

Answer 5

Outer 1/3 of EAM cartilaginous

Inner has a bone

Question 6

Cerumen is produced in what part of the ear canal?

Answer 6

Epidermal lining of the outer portion of the ear canal contains hair follicles and glands that secrete cerumen

Question 7

What is the function of cerumen?

Answer 7

Protection - keeps from drying out, slight antibacterial functions, repel insects

Question 8

The ear canal primarily acts like what kind of resonator?

Answer 8

Acts as an open-closed pipe resonator

Peak of filter is broadly tuned at closed end (TM is not completely reflective)

Question 9

At what frequency is the primary resonance of the ear canal and meatus?

Answer 9

2 - 3 kHz

Question 10

What parts of the body contribute to the resonances by the time one reaches the tympanic membrane?

Answer 10

Head torso and pinna

Question 11

What portion of the Eustachian tube is surrounded by cartilage? Bone?

Answer 11

First 1/3 has a bony foundation, remaining 2/3 is cartilaginous
Isthmus is where they meet.

Question 12

Which nerve runs next to the middle ear cavity?

Answer 12

Facial nerve (Vll)– runs along the posterior side of the ear canal

Question 13

What is the promontory? What is its function?

Answer 13

The promontory is a rounded prominence formed by the lateral projection of the basal turn of the cochlea

Positioned to protect the oval and round windows in that it directly faces the middle ear cavity

Question 14

What vein runs next to the inferior wall of the middle ear cavity? What type of tumor is common to destroy this wall?

Answer 14

Jugular vein

Glomus jugular

Question 15

The children the Eustachian tube is roughly at what angle? In adults?

Answer 15

In adults- 30-45o angle from the anterior wall of the middle ear cavity to the posterior wall of the nasopharynx

Children - more horizontally positioned, lays almost parallel with the pharyngeal ostium

Question 16

What are the names of the ossicles?

Answer 16

Malleus incus and stapes

Question 17

The middle ear bones solve what major problem in the transduction of sound?

Answer 17

The impedance mismatch problem – transforming the signal from a medium of low impedance (air) to a medium with high impedance (cochlear fluid)

When sound wave meets a higher impedance medium, energy is normally reflected

Question 18

What are the three mechanisms that the ossicles improve sound transduction?

Answer 18

1. Area difference between the TM and the stapes footplate
2. Lever effect that is provided by the ossicular chain
3. Buckling effect of the ossicular chain

Question 19

The tympanic membrane moves in what direction?

Answer 19

More movement at the inferior margin

Question 20

Which of the ossicles is the weakest and most likely to break?

Answer 20

Incus – long process is the contact point for the stapes and is the weakest point in the ossicular chain