Cochlear Anatomy

Question 1

Where is the cochlea housed?

Answer 1

Petrous portion of the temporal bone

Question 2

What boney element surrounds the cochlea?

Answer 2

Otic Capsule

Question 3

What are the types of temporal bone fractures? How often do they each occur? Which is worse?

Answer 3

Longitudinal: courses along the long axis of the temporal bone, often are a result of a severe blow to the temporal or parietal area of the head, over 70% of temporal bone fractures are longitudinal in nature

Transverse: orientated perpendicular to the long axis of the petrous temporal bone, generally through otic capsule and IAM (this one is worse; 50% chance of resulting in facial palsy)

Question 4

The cochlea has how many turns?

Answer 4

2.2-2.9 turns, smaller at apex than base

Question 5

How long is the average cochlea?

Answer 5

25 - 35 mm

Question 6

The central axis of the cochlea is called what?

Answer 6

Modiolus: central, perforated bony core that accommodates nerve fibers from the hair cells, as well as blood vessels

Question 7

What is the function of the spiral lamina?

Answer 7

Two thin plates between auditory nerve fibers pass from hair cells to cochlea. Also a support point and connector for the inner BM.

Attachment and support for the tectorial membrane

Question 8

What are the 3 scala and where are they located?

Answer 8

Scala vestibuli: superior

Scala media: in the middle

Scala tympani: inferior

Question 9

What divides the 3 scala and where are they located?

Answer 9

Basilar membrane: connected to the spiral ligament on the outer wall of the bony cochlear and to the osseous spiral lamina to form the floor of the scala media

Reissner’s membrane: forms the roof of the cochlear duct and the floor of scala vestibuli

Question 10

Describe the size and stiffness of the basilar membrane.

Answer 10

Wider, more flaccid, and under no tension at the apical end

Stiff at the basal end

Allows better tuning for high frequencies at the base and low frequencies at the apex

Question 11

What is the main organ of hearing?

Answer 11

Organ of Corti

Question 12

What gelatinous flap of collagen lies above the organ of Corti?

Answer 12

Tectorial Membrane

Question 13

What is the purpose of the stria vascularis?

Answer 13

Maintains the chemical relationship in the endolymph (high K+ ions and low Na+ ions)

Question 14

What are the two types of hair cells? What are their shapes? How many are there of each?

Answer 14

IHCs: a single row of IHCs course the length of the cochlea and number about 3500 cells, flask shaped

OHCs: three to five rows, about 12000 cells, cylinder shaped, long in regions of low frequencies and shorter in regions of high frequencies

Question 15

What shape are the two types of hair cells arranged?

Answer 15

IHCs: stereocilia are flat U-shaped

OHCs: 3 rows of stereocilia form a W shape

Question 16

Which of the hair cells have contractile proteins? Why do they have them?

Answer 16

The OHCs have contractile proteins (actin, myosin, prestin, tubulin)

Chemical elements are necessary for the rapid expansion and contraction of the OHCs

Question 17

Which hair cells are the main transducers of sound?

Answer 17

Inner hair cells

Question 18

What are the two windows of the cochlea? Where are they located (which is superior)? What is attached to them?

Answer 18

Oval window (superior) – interacts with the stapes of the middle ear and opens into the scala vestibuli

Round window (inferior) – interacts with the scala tympani