Auditory & Vestibular Systems

Question 1

Auditory - stimulus & receptor

Answer 1

Stimulus = pressurized sound wave

Receptor = hair cell

Question 2

3 areas of auditory system

Answer 2

1. outer ear - sound waves are collected & travel to tympanic membrane
2. middle ear - tympanic membrane to cochlea
   - contains the 3 bones: malleolus, incus & stapes - stapes attaches to oval window
3. Inner ear - past stapes bone including cochlea & labrynth

Question 3

Cochlea

• anatomy
• function

Answer 3

Contains organ of corti

• sits on basilar membrane
• contains 3 outer hair cells (accept sound) and connect to one inner hair cell (fine tune the sound)

The hair cells are stimulated by the tectorial membrane which moves in response to pressure variations in the fluid

Function: hearing

Question 4

Stimulation - electrical potential @ hair cell during hearing

Answer 4

@ cilia, K rushes in, causing depolarization
Ca rushes in
release of excitatory NT
–> sound transmitted via cochlear nerve (CN VIII)

Question 5

Tonotropic arrangement in the cochlea

Answer 5

higher frequencies stimulate hair cells @ BASE of the cochlea

lower frequencies travel further and stimulate hair cells @ APEX of cochlea

Question 6

Functions of Auditory system (3)

Answer 6

1. Activating effect of sound (alert/arousal)
2. Orients head and eyes toward sound
   (inferior colliculus - info from both ears, then travels to superior colliculus - responsible for turning of head)
3. Recognition of sound

Question 7

Primary Auditory Cortex

• location
• function

Answer 7

Area 41 of temporal lobe

Function: conscious awareness of intensity of sound (loudness & pitch)
- contains same tonotrophic arrangement as cochlea

Question 8

Secondary Auditory Cortex

• location
• function

Answer 8

Areas 22,42 of temporal lobe

Function: classification of sounds - dog barking? bell ringing

comparing sounds w/ memories of other sounds

Question 9

Wernicke’s area

Answer 9

responsible for comprehension of sound

Question 10

Vestibular System

- functions (3)

Answer 10

1. perceive motion
2. Maintain balance (vestibule-spinal reflex)
3. Stabilize eyes (VOR)

Question 11

3 systems w/n Vestibular system

Answer 11

1. Peripheral sensory apparatus - located in inner ear - labrynth
2. Central processing system - located in vestibular nuclei complex in BS
3. Motor systems - ocular & skeletal muscle control

Question 12

Peripheral Sensory Apparatus of Vestibular system

• function
• composed of

Answer 12

Function: provide sensory input about angular & linear acceleration and orient head w/ respect to gravity to maintain stable gaze

Composed of: semicircular canals, otoliths (utricle & saccule) and ampulla

Question 13

Semicircular canals (3)
- function

Answer 13

filled w/ endolymph, sensitive to yaw, pitch & roll planes and all 3 are oriented in right angles to eachother

1. anterior (sup) = sagittal movement (flex/ext)
2. posterior (inf) = lateral side bending of the head
3. horizontal (lateral) = axial rotation
   - sits at 30deg

Question 14

Otoliths

• saccule & utricle
• function

Answer 14

Used for balance control, hair cells send signal to postural muscles

Saccule: macula oriented in horizontal plane, maximally stimulated w/ linear mvmt

Utricle: macula oriented in vertical plane

Question 15

Ampulla

• what is it
• function

Answer 15

expansion that connects utricle w/ distal end of semicircular canal; contains crista ampullaris & hair cells

Function: convert head motion to neuronal firing (via hair cells)

Question 16

Central Processing System of Vest system

• composed of
• how does it work

Answer 16

Composed of 4 vestibular nuclei - each which maintains a baseline firing rate that is SYMMETRICAL @ REST

• head movements cause change in firing rates of both vestibular nerve but in opposite direction….
• -> turn head to the R, R fires FASTER & vice versa

IF this is messed up it will cause a nystagmus

Question 17

Motor systems of Vestibular system

• function
• tracts involved

Answer 17

Function: generate compensatory eye movements for gaze stability and body movements to maintain posture and body equilibrium w/ locomotion

1. MLF - connects directly to eye muscles via CN III, IV and VI
2. Medial vestibulospinal tract - maintains UE and head position
3. Lateral vestibulospinal tract - maintains stability of trunk and LE

Question 18

Physiology behind Semicircular canals

Answer 18

3 coplanar pairs are formed between R&L
–> this paring is associated w/ push-pull change in quantity of semicircular canal output (2 mechanisms are sending the same message to the brain)

Example:
Turn your head to the right you stimulate the R horizontal canal while the L horizontal canal is inhibited… OR
Flex head - stimulates R ant canal & inhibits L posterior

Each canal has its own signature eye movement which makes it important for testing for which canal may be contributing to problem

Question 19

Functions of Semicircular canals vs. Utricle & Saccule

Answer 19

Semicircular canals - respond to ANGULAR ACCELERATION

Saccule & Utricle - repsond to LINEAR acceleration and head position in gravity

Question 20

Why is Vestibular Contribution to Eye movement important?

Answer 20

1. Gaze stability (VOR)
2. Overriding VOR - conscious decision to turn your head
3. Optokinetic reflex - slower movement, larger perception

Question 21

Vestibular-ocular Reflex (VOR)

• what is it
• regulated by
• deficit

Answer 21

Maintain gaze stability during head motion which allows the desired object to stay on fovea, even when walking/ running or moving your head

Regulated by semicircular canals

Deficit = oscillopsia

EXAMPLE: turn your head to the right - R medial rectus (CN III) and L lateral rectus (CN VI) to maintain gaze straight

Question 22

VOR Gain

Answer 22

head and eye movement of equal velocity which is regulated by semicircular canals

Vestibular system is responsible for maintaining gaze > 60deg/sec

CNS responsible for smooth pursuit (

Question 23

How to test VOR?

Answer 23

Smooth pursuit - CNS - track finger

Saccades - vestibular system - look at tip of nose, then finger

VOR - tilt head down to 30 to maximally stimulate horizontal canals - perform quick movements while staring at nose

Question 24

Nystagmus & VOR

• what is it
• which way does the fast beat go

Answer 24

differences between sides in the tonic firing rate w/n vestibular nuclei, indicating one is more active than the other

Fast beat - towards more ACTIVE side (stimulated ear) b/c it will drift to the weaker, less active side

Question 25

Nystagmus & Peripheral lesion

Answer 25

beats AWAY from the side w/ a deficit-causing lesion TOWARD side w/ an irritative lesion

Question 26

Nystagmus & CNS

Answer 26

no pattern

Question 27

BPPV - what is it - symptoms

Answer 27

single most common cause of dizziness common in >65 due to otoconia falling out of place (vestibular degeneration), which displace the fluid and stimulate hair cells when they are not moving Symptoms arise w/ change in head position & is usually unilateral

Question 28

Meniere's Disease - what is it - what does it cause

Answer 28

malabsorption of endolymph due to drainage system being blocked which increases swelling Causes: fullness in ear, reduced hearing, rotational vertigo & nausea Constantly tells your brain your moving causing dizziness for days (Meneire's attack) - 48-72 hours Increase prevalence of migranes and can lead to deterioration of auditory & vestibular systems

Question 29

Oscillopsia - what is it - what causes it

Answer 29

apparent movement of a stationary visual environment can be due to bilateral vestibular loss, dysfunction of semicircular canals leading to deficit of VOR - caused by ototoxicity from taking gentamycin If loss is equal bilaterally, no complaints of vertigo

Question 30

Central vs. Peripheral Disorders of Vestibular system

Answer 30

Central - damage to vestibular nuclei, pathways or BS/cerebellum - Symptoms: oscillopsia (impaired VOR), nausea, disquilibrium (balance), impaired smooth pursuit, diplopia Peripheral - damage to peripheral sensory apparatus (i.e. BPPV, Menieres, neuritis, labryinthis, etc) - Symptoms: hearing loss, vertigo, tinnitus, fast beating nystagmus, gait ataxia, impaired VOR

Question 31

Contraindications to Vestibular Treatment (4)

Answer 31

unstable vestibular disorders (acute PLF) recent surgeries acute TBI positive vertebra-basilar insufficiency test