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Neuroanatomy > Auditory & Vestibular Systems > Flashcards

Auditory & Vestibular Systems Flashcards

1
Q

Auditory - stimulus & receptor

A

Stimulus = pressurized sound wave

Receptor = hair cell

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2
Q

3 areas of auditory system

A
  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
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3
Q

Cochlea

  • anatomy
  • function
A

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

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4
Q

Stimulation - electrical potential @ hair cell during hearing

A

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

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5
Q

Tonotropic arrangement in the cochlea

A

higher frequencies stimulate hair cells @ BASE of the cochlea

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

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6
Q

Functions of Auditory system (3)

A
  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
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7
Q

Primary Auditory Cortex

  • location
  • function
A

Area 41 of temporal lobe

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

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8
Q

Secondary Auditory Cortex

  • location
  • function
A

Areas 22,42 of temporal lobe

Function: classification of sounds - dog barking? bell ringing

comparing sounds w/ memories of other sounds

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9
Q

Wernicke’s area

A

responsible for comprehension of sound

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10
Q

Vestibular System

- functions (3)

A
  1. perceive motion
  2. Maintain balance (vestibule-spinal reflex)
  3. Stabilize eyes (VOR)
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11
Q

3 systems w/n Vestibular system

A
  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
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12
Q

Peripheral Sensory Apparatus of Vestibular system

  • function
  • composed of
A

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

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13
Q 
Semicircular canals (3)
- function
A

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
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14
Q

Otoliths

  • saccule & utricle
  • function
A

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

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15
Q

Ampulla

  • what is it
  • function
A

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)

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16
Q

Central Processing System of Vest system

  • composed of
  • how does it work
A

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

17
Q

Motor systems of Vestibular system

  • function
  • tracts involved
A

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
18
Q

Physiology behind Semicircular canals

A

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

19
Q

Functions of Semicircular canals vs. Utricle & Saccule

A

Semicircular canals - respond to ANGULAR ACCELERATION

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

20
Q

Why is Vestibular Contribution to Eye movement important?

A
  1. Gaze stability (VOR)
  2. Overriding VOR - conscious decision to turn your head
  3. Optokinetic reflex - slower movement, larger perception
21
Q

Vestibular-ocular Reflex (VOR)

  • what is it
  • regulated by
  • deficit
A

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

22
Q

VOR Gain

A

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 (

23
Q

How to test VOR?

A

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

24
Q

Nystagmus & VOR

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

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

25
Q

Nystagmus & Peripheral lesion

A

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

TOWARD side w/ an irritative lesion

26
Q

Nystagmus & CNS

A

no pattern

27
Q

BPPV

  • what is it
  • symptoms
A

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

28
Q

Meniere’s Disease

  • what is it
  • what does it cause
A

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

29
Q

Oscillopsia

  • what is it
  • what causes it
A

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

30
Q

Central vs. Peripheral Disorders of Vestibular system

A

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

31
Q

Contraindications to Vestibular Treatment (4)

A

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

Neuroanatomy (15 decks)

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