Physiology of Auditory and Vestibular Systems

Question 1

What is the audible range of frequencies?

Answer 1

20-20,000 Hz

Question 2

Sound waves over ___ dB can cause pain and damage to the cochlea

Answer 2

120

Question 3

What kind of fluid is contained within the membraneous labyrnith?

Answer 3

endolymph

Question 4

What kind of fluid surrounds the membranous labyrinth between the bony labyrinth?

Answer 4

perilympth

Question 5

What is characteristic of endolymph?

Answer 5

it is low in [Na+] and high in [K+]

Question 6

what is characteristic of perilymph?

Answer 6

it is high in [Na+] and low in [K+]

Question 7

Why do sound waves need to be amplified?

Answer 7

Differences in density between air and liquid or else there would only be 1% transmission of sound energy

Question 8

describe the process of hearing in the middle ear

Answer 8

1. sound waves cause the tympanic membrane to vibrate
2. in turn, the ossicles (malleus, incus and stapes) vibrate, pushing the stapes into the oval window of the cochlea and displacing cochlear fluid

Question 9

What is impedance matching and what does it do?

Answer 9

amplifying the sound wave to improve transmission

Question 10

Where is the cochlea and what does it contain?

Answer 10

It is located in the inner ear within the bony labyrinth and contains 3 fluid filled canals called scala vestibuli, scala tympani, and scala media

Question 11

What is significant about scala vestibuli and scala tympani?

Answer 11

both contain perilymph (high in [Na+] and low in [K+])

Question 12

what is significant about about the scala media?

Answer 12

It contains endolymph (high [K+] and low [Na+]) and borders the basilar membrane which is the site of the organ of Corti

Question 13

what is the organ of Corti?

Answer 13

Contains inner and outer hair cells embedded in the tectorial membrane that are receptors for auditory stimulus

Question 14

Describe the differences in inner and outer hair cells within the organ of corti

Answer 14

Outer hair cells are more numerous but inner hair cells have more innervation and are the receptors connected to the CNS. Inner hair cells are though to be the hair cells that actively “hear” sound

Question 15

What is the mechanism of sound transduction?

Answer 15

1. Sound waves cause a vibration of the organ of Corti
2. This causes vibration of the basilar membrane and the hair cells bend by a shearing force as they push against the tectorial membrane
3. Bending of the cilia causes a change in K+ conductance of the hair cell membrane
4. Due to a combined +140 mV total potential difference (+60 mV potential difference of perilymph and inner hair cell added to +80 mV potential difference of endolymph to peilymph) this favors movement of a cation into the cell if there is an open channel for it

Question 16

What causes the opening or closing of ion channels in cochlear transduction?

Answer 16

the links between the cilia, called tip-link adhesion molecules, depending on the direction fo the cilia

Question 17

Describe the electrical process and result of cilia bending towards the tallest member

Answer 17

1. opening of stretch-activated K+ channels
2. K+ enters the hair cell and depolarizes it
3. Voltage-gated Ca+ channels open resulting in increased neurotransmitter release and overall increased rate of AP towards the axis of polarity

Question 18

Describe the electrical process and result of cilia bending toward the smallest member

Answer 18

1. Closing of stretch-activated K+ channels
2. No K+ entry into the hair cell so it becomes hyperpolarized
3. Ca+ channels close and there is no neurotransmitter release and thus no APs away from the axis of polarity

Question 19

What is the Place theory Coding System?

Answer 19

Based on the basilar membrane, the base is stiffer and more responsive to high-frequency sounds whereas the apex is more compliant and more responsive to low-frequency sounds. Used for above 2000 Hz.

Question 20

What is the Volley Theory Coding System?

Answer 20

Only used for low tones, frequencies under 400 Hz. Each neuron responds to a sound by firing APs slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain

Question 21

What is temporal summation?

Answer 21

occurs when one presynaptic neuron releases neurotransmitters over a period of time to fire an action potential

Question 22

What is spatial summation?

Answer 22

occurs when multiple presynaptic neurons release neurotransmitters together to fire an action potential in the postsynaptic neuron

Question 23

Where are receptor hair cells found in the semicircular canals?

Answer 23

in the crista ampullairis, located within the ampulla and the cilia are embedded in a gelatinous mass called the cupula

Question 24

what is the kinocilium?

Answer 24

the longest cilia of a hair cell

Question 25

What is the axis of polarity for the horizontal semicircular canal?

Answer 25

towards the utricle

Question 26

what is the axis of polarity for the anterior and posterior semicircular canals?

Answer 26

away from the utricle

Question 27

What do semicircular canals detect?

Answer 27

angular or rotational acceleration

Question 28

Describe the mechanical transduction mechanism that occurs within semicircular canals

Answer 28

1. rotation of the head causes movement of the endolymph in the opposite direction
2. the endolymph pushes against the cupula and bends the hair cell fibers
3. when constant velocity is reached, both the head and endolymph are traveling in the same direction at the same velocity
4. stopping rotation does not stop the endolymph as quickly, resulting in the post-rotational response

Question 29

What does the utricle detect? and provide examples

Answer 29

linear acceleration in the horizontal plane. examples include tilting of the head, and forwards/backwards movement

Question 30

what does the saccule detect? and provide examples

Answer 30

linear acceleration in the verticle plane. examples include gravity and up/down movement

Question 31

What are the otolith organs and where are they contained?

Answer 31

Otolith organs are the utricle and saccule, contained within a thickened area called the macula. Cilia are embedded in the otolith membrane covered by otoconia

Question 32

Describe the mechanical vestibular transduction mechanism that occurs in the otolith organs

Answer 32

1. Tilting of the head causes movement of the endolymph to displace the otolith membrane and otoconia
2. hair cell fibers bend
3. because the striata depression changing the axis of polarity, there are opposite discharge effects on the two sides of the striata