13. CNVIII - Orientation and Audition

Question 1

Pathway of sound transmission from environment to organ of corti

Answer 1

Environment –> auricle –> external auditory meatus –> tympanic membrane –> malleus –> incus –> stapes –> oval window –> scala vestibuli –> organ of corti

Question 2

Perilymph vs endolymph composition

Answer 2

Perilymph: resembles ECF, low K+, high Na+
Endolymph: resembles cytoplasm, high K+, low Na+

Question 3

What is endolymph secreted by?

Answer 3

Endolymph is secreted by stria vascularis (part of spiral ligament)

Question 4

Describe the endolymph flow

Answer 4

In the cochlea, endolymph flows from stria vascularis –> cochlear duct –> saccule –> endolymphatic duct

In the vestibular system, endolymph flows from semicircular ducts –> utricle –> endolymphatic duct

Question 5

What is meniere’s disease?

Answer 5

Increased hydraulic pressure in inner ear. Idiopathic cause

Question 6

The scala vestibuli, scala tympani, and scala media have endolymph or perilymph? (Which has which)

Answer 6

Scala vestibuli = perilymph
Scala media = endolymph
Scala tympani = perilymph

Question 7

What is the modoilus?

Answer 7

Central bony structure in cochlea that belongs to bony labyrinth. Cochlea winds around modiolus

Question 8

Sound waves are which type of waves?

Answer 8

Longitudinal aves

Question 9

What is the helicotrema?

Answer 9

Tip of the cochlea, connnects the scala vestibuli and the scala tympani

Question 10

What does the round window do?

Answer 10

presses outwards to relieve pressure from the fluid

Question 11

Tonotopic organization, higher frequency sound vs lower frequency sound

Answer 11

The basilar membrane is organized so that higher frequency sound causes the membrane to vibrate closer to the base (more stiff). The lower frequency sound causes the membrane to vibrate closer to the apex (flexible)

Question 12

How does the movement of the basilar membrane occur?

Answer 12

Fluid of scala vestibulae is moved, causing basilar membrane to move. Basilar membrane vibrates optimally at specific freqeunces at specfic locations

Question 13

Which gyrus is associated with primary auditory cortex?

Answer 13

Transverse temporal gyrus

Question 14

Where do lower frequency sounds get relayed to in the primary auditory cortex

Answer 14

More peripheral in the temporal gyrus

Question 15

If I am right handed, what is my dominant hemisphere?
Which hemisphere is dominant for language, math, problem solving?
Which hemisphere is dominant for musical skills, recognition of faces, spatial relationship?

Answer 15

Right handed means left hemisphere is dominant
Left hemisphere dominant for language math problem solving
Right hemisphere dominant for musical skills, recognition of faces, spatial relationship

Question 16

What does a cochlear implant do?

Answer 16

Excites organ of corti

Question 17

Type 1 vs type 2 hair cells

Answer 17

Type 1 hair cell: inner hair cell

Type 2 hair cell: outer hair cell

Question 18

As organ of corti is moved upwards, hair cells move ____.

As organ of corti is moved downwards, hair cells move _____.

Answer 18

right

left

Question 19

Hair cells in the organ of corti are embedded in the _____

Answer 19

tectorial membrane

Question 20

Hair cells are connected to each other via

Answer 20

tip links

Question 21

Steriocilia are made of ____, the same as _______.

_______, on the other hand, are made of _______.

Answer 21

Steriocilia are made of actin, the same as microvilli.

Cilia, on the other hand, are made of microtubules

Question 22

What gradient causes the flow of K+ from endolymph to inside the hair cells in the organ of corti?

Answer 22

Electrical gradient (endolymph is already much like the intracellular fluid, so chemical gradient does not really contribute)

Question 23

Is the direction that the stereocilia move important?

Answer 23

Yes, stimulate in opposite direction does not result in a response

Question 24

Sensori-neural hearing loss can occur with prolonged exposure to sound at what level?

Answer 24

> 90dB

Question 25

Difference in function between Type 1 and Type 2 hair cells

Answer 25

Type 1 = AFFERENT, have the sensory information of sound

Type 2 Hair cells - EFFERENTS, contraction of outer hair cells to increase sound descrimination

Question 26

Loss of what cell type would result in tone-deafness?

Answer 26

Type 2 hair cells

Question 27

Loud noises cause the contraction of which two muscles?

Answer 27

Stapdeius muscle (CN VII) and tensor tympani muslce (CN V)

Question 28

Where does the tensor tympani muscle attach?

Answer 28

Malleus handle

Question 29

Say the auditory neural pathway

Answer 29

Nerves from cochlea carry info via the spiral ganglion to the dorsal cochlear nucleus –> B/L to superior olivary n (some fibers decussate at trapezoid body) –> inferior colliculus –> medial geniculate n in thalamus –> transverse temporal gyrus in primary auditory cortex

Question 30

What is time shift (in reference to sound source localization in auditory system)?

Answer 30

If a sound source is closer to your right side, then the right ear will hear it first, transmitting the signal to the superior olivary nucleus first.

Question 31

Tone difference for sound localization

Answer 31

If a sound source is to your right, then the right ear will hear the full range of frequencies/tones, and the left ear will have some of those frequencies/tones removed

Question 32

What is sensori-neural hearing loss?

Answer 32

Hearing loss due to a neural problem

Question 33

Define sensory aprosodia

Answer 33

Difficulty understanding meaning conveyed by tone of voice (diff understanding sarcasm)

Question 34

Define motor aprosodia

Answer 34

Difficulty conveying meaning through tone of voice (monotone)

Question 35

What kind of acceleration do the semicircular canals measure?

Answer 35

Angular acceleration (basically, head movements)

Question 36

What kind of acceleration and motion do the utricle and saccule measure?

Answer 36

linear acceleration (running forward, car motions, etc)

Saccule: sagittal plane (up and down)
Utricle: left to right, forwards and backwards

Question 37

Ampulla, cupulla, crista, stereocilia anatomy

Answer 37

Ampulla is a dilation at end of semicircular canal. Contains hair cells whose cell bodies are embedded in the crista. Their stereocilia are embedded in the cupulla a gelatinous membrane containing otoliths

Question 38

Information from the vestibular ganglion goes to which nuclei?

Answer 38

Vestibular nuclei

Question 39

Where can the information go from the vestibular nuclei?

Answer 39

Extraoccular muscle, thalamaus/sensory cortex, cerebellus, postural compensation, head position & eye movements

Question 40

Vestibuloocular reflex

Answer 40

Gaze stays fixed on an object while the head is moving

Question 41

If you have a left beating nystagmus, what does that mean?

Answer 41

It means you have a rapid phase to the left with optokinetic (watching moving objects)

Question 42

If you squirt cold water into an ear, what happens?

Answer 42

cause nystagmus

Question 43

What happens with Benign paroxysmal positional vertigo (BPPV), and how do you treat it?

Answer 43

Otoconia break off the membrane and get lodge elsewhere (increased incidence with age)
Tx: Canalith repositioning procedure

Question 44

What happens with alcohol-induced vertigo (bed-spins)

Answer 44

Alcohol is less dense than water, causing the cupula to float. Gives you sensation of rotation. When upula sinks, get sensation of rotation again