Exam 3 Week 14 ppt 8 outer, middle, inner ear

Question 1

Function of auditory system

Answer 1

Detects and analyzes sounds from the environment

Question 2

What makes up the outer ear?

Answer 2

• Consists of pinna & external auditory meatus

- Tympanic membrane separates outer and middle ear

Question 3

What makes up the middle ear?

Answer 3

-Within the temporal bone
-Air-filled cavity Contains:
3 ear ossicles: malleus, incus, and stapes
2 muscles – tensor tympani & stepedius

Question 4

What happens inside middle ear?

Answer 4

Vibrations of tympanic membrane conducted by ear ossicles to vibrate oval window

Question 5

Why is there a 25 fold increase in pressure on oval window compared to tympanic membrane?

Answer 5

• Different size of membranes

- Mechanical advantage ear ossicles

Question 6

What can control conduction of the vibrations in middle ear?

Answer 6

Tensor tympani

Question 7

Tensor tympani innervated by ______

Answer 7

CN V

Question 8

What controls controls the movement of the stapes?

Answer 8

Stapedius

Question 9

Stapedius innervated by _________

Answer 9

CN VII

Question 10

How do Stapedius and tensor tympani work?

Answer 10

Reflexive contraction to lessen movement & sound conduction (lower the acuity of the sound)

Question 11

What makes up the inner ear?

Answer 11

Separated from middle ear by oval & round windows

1. Cochlea- Spiral bony container, wound around central core – Modulus, bipolar cells of spiral ganglion in modulus
2. Fluid filled- Perilymph between bony & membranous labyrinth, Several membranous structures form the cochlear duct, Endolymph in cochlear duct
3. 3 chambers- Scala vestibuli (1) & scala tympani (2) – filled with perilymph Scala media (3) (cochear duct), formed by vestibular & basilar membranes, filled with Endolymph

Question 12

The pathway of vibrations in the inner ear

Answer 12

• Vibrations in perilymph produced by vibration of oval window
• Vibrations carried down the scala vestibuli & around the heliotrema into the scala tympani
• This vibrates the basilar membrane

Question 13

Basilar Membrane- 3 points to know

Answer 13

1. Varies in width and stiffness from base to apex of cochlea
2. Thinner & more compliant near oval window – vibrated by higher frequency vibrations of perilymph
3. Thicker & stiffer toward cochlear apex – vibrated by lower frequency vibrations of perilymph

Question 14

Tonotopic map of cochlea

Answer 14

Highest frequencies base

Lowest frequencies apex

Question 15

Where does auditory transduction occur?

Answer 15

in the hair cells of the organ of Corti

Question 16

Structures of the organ of Corti

Answer 16

1. Outer & inner rows of hair cells rest on basilar membrane
2. Tectorial membrane is gelatinous shelf resting on stereocilia of the outer hair cells
3. Bipolar cell processes of the spiral ganglion surround base of hair cells

Question 17

What holds together structures of the organ of Corti?

Answer 17

supporting cells

Question 18

Where are the hair cells?

Answer 18

Positioned within the endolymph-filled scala media

Question 19

Numbers and hair cells

Answer 19

3500 flask-shaped inner hair cells

>15,000 cylindrical outer hair cells

Question 20

Differences between inner and outer hair cells (7)

Answer 20

1. Inner on least flexible portion of basilar membrane
2. Outer on most flexible portion
3. Inner hairs do not touch tectorial membrane – outer do
4. Outer hair cells depolarized by pivoting hair cells against tectorial membrane
5. Inner hair cells depolarized by movement of endolymph in inner spiral sulcus
6. 95% of afferent axons in cochlear nerve receive their input from inner hair cells
7. Only 5% receive it from outer hair cells

Question 21

Role of outer hair cells (3)

Answer 21

1. Outer hair cells have motor proteins activated by depolarization of hair cell
2. Shortens outer hair cell
3. Amplifies movement of basilar membrane up to 100 fold