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Chika- SF2 > Auditory-Vestibular- Wilson > Flashcards

Auditory-Vestibular- Wilson Flashcards

1
Q

Where is the vestibulocochlear nerve located?

A
  • found at the pontomedullary junction

- CN VIII enters the brain as 2 roots at the junction of the pons and medulla

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2
Q

What are the two divisions of the vestibulocochlear nerve? Which is medial and lateral?

A 
vestibular root (medial) 
auditory root (lateral
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3
Q

Once CN VIII exits the posterior cranial fossa it enters the petrous portion of the temporal bone via?

A

internal acoustic meatus

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4
Q

What is the most common tumor of cranial nerves do humans encounter?

A

acoustic neuroma AKA vestibular schwannoma

-a tumor that grows from the nerves responsible for balance and hearing. (vestibulocochlear nerve)

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5
Q

Where is the vestibulocochlear apparatus and auditory labyrinths embedded?

A

petrous temporal bone

-contains the special organs of hearing and balance

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6
Q

CN VIII has what 3 sensory ganglia containing first order bipolar neurons?

A

2 vestibular ganglia:
-inferior and superior ganglion

1 spiral ganglion: contains bipolar neurons for hearing

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7
Q

The first order neurons of the vestibular pathway that form the vestibular nerve come from what kind of cells?

A

bipolar neurons

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8
Q

Where do the axons of the bipolar cell from the 2 vestibular ganglion project to?

A

1) cerebellum: specifically the flocculonodular node and vermis; they receive direct afferents from CN VIII
- vermis is more central and also receives a very direct input from CN VIII
- flocculonodular lobe is the vestibular part of the cerebellum, involved in processing information for balance, eye movement, etc

2) 4 vestibular nuclei: the second order neurons
- lateral
- medial
- superior
- inferior (descending)

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9
Q

What is the only cranial nerve in which the cerebellum receives direct afferents?

A

CN VIII

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10
Q

Where are the 4 vestibular nuclei found in the brain?

A

in the rostral medulla and caudal pons

  • 4th ventricle has been removed
  • they form a diamond shape on the floor of the 4th ventricle
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11
Q

What is important about the superior vestibular nucleus?

A

it gives axons to the ipsilateral medial longitudinal fasciculus (MLF) which is major highway for interconnecting the motor nuclei controlling eye movements

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12
Q

What is the medial vestibulospinal tract?

A

a descending tract that controls movements/extensions of the neck to head movements which comes from the medial vestibular nucleus

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13
Q

Why is the lateral vestibular nucleus important?

A

forms the lateral vestibulospinal tract which is a descending tract that helps to control excitation of anti-gravity muscles (these cause extension of our paraspinal muscles and limbs to keep us standing up and maintaining erect posture)

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14
Q

List the vestibular outputs.

A
  • extraocular motor nuclei via MLF
  • cerebellum (reciprocal connections)
  • ventral posterior nucleus of thalamus
  • reticular formation
  • spinal cord
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15
Q

Is there a vestibular portion in the cortex?

A

No there is not but there is relay of vestibular information through a thalamic nucleus to the cortex

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16
Q

Where is vestibular information relayed to get to the cortex?

A

ventral posterior nucleus of thalamus

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17
Q

What is the reticular formation?

A
  • receives collaterals from ascending tracts
  • forms the core of the medulla, pons, and midbrain
  • gets input from pain, auditory, etc. fibers
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18
Q

Extraocular motor nuclei via MLF

What are these nuclei and what functions do they serve?

A
  • abducens motor nuclei in the pons
  • oculomotor motor nuclei in the midbrain

horizontal gaze; for movements looking laterally and adjustment to head movements going to the opposite direction or producing nystagmus

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19
Q

How does the vestibular system connect to these extraocular motor nuclei and how do they control eye movement?

What is significant about the neuronal activity of the vestibular nuclei on the right and left hand side?

A

abducens nucleus that controls lateral rectus
oculomotor nucleus control medial rectus

two types of neurons in abducens nucleus

  • motor neurons that go to the lateral rectus
  • interneurons that project to the contralateral oculomotor via MLF to the medial rectus
  • this allows for conjugate movement of the eyes (move at the same direction)

the cells in the vestibular nuclei of the left and right eye are firing at the same frequency and thus the eyes are able to look straight forward

If they are not firing at the same time the head eyes will move in the opposite direction; if inhibited eyes will move in the same direction as the head

23:00

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20
Q

What is nystagmus?

A
  • it is a result of imbalance of the vestibular nuclei on both sides
  • there is a slow phase AKA compensatory eye movement
  • there is a fast phase where there is correction by the cortex to reset the eyes
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21
Q

Slow phase of nystagmus is controlled by?

A

slow phase AKA compensatory eye movement

  • turning the head right or left
  • irrigating the ear with warm or cold water
  • pathological disruption of vestibular nuclei
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22
Q

How do you define nystagmus clinically?

A

by the fast phase which is controlled by the cortex

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23
Q

What is caloric stimulation of the vestibular system (COWS)?

A

when you have a pt that is unconscious due to anesthesia or head injury; you place warm or cold water into the external auditory meatus

  • used to access the degree of coma; warm or cold water is injected into an ear, stimulating the semicircular canals
  • normally nystagmus (rhythmic beating of the eyes) is evoked
  • failure to produce nystagmus is a poor sign indicating severe brain injury
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24
Q

Describe the process of caloric stimulation.

A

when you irrigate the external auditory meatus with warm or cold water we’re causing, through convection currents, endolymphatic movement (it’s the same result as when we move our head a certain direction)

it is the same endolymphatic movement in the vestibular system that you use for head movements; we can ARTIFICIALLY produce that by producing a difference in temperatures
so the endolymphatic movement starts to move in one direction

if you irrigate with warm water it is the same when you move you head in the opposite direction that the endolymphatic flow goes; as a result warm water results in an increased firing in the vestibular nerve thus increased firing in the vestibular nuclei; the excitatory activity becomes heavier creating an imbalance

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25
Q

Describe the role of the vestibular system in the VOR.

A

????

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26
Q

Describe the normal circuit for the VOR and its importance to the visual system.

A
  1. Endolymph flow stimulates hair cells of RIGHT ear
  2. Increases nerve firing rate
  3. Stimulate vestibular nucleus
  4. Both eyes look LEFT
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27
Q

Indicate the effects of all brainstem lesions to eye movement and the two phases of horizontal nystagmus as indicated on the next image.

A

???

28
Q

If there is a stroke on the left vestibular nuclei what is the result?

A

nystagmus due to the stroke on the left vestibular nuclei producing imbalance

the nystagmus is towards the opposite direction of the stroke

29
Q

What happens when you irrigate the left ear with cold water?

A

you inhibit the vestibular apparatus on the left side and generate a nystagmus going in the OPPOSITE direction

30
Q

The vestibulo-ocular reflex is a very robust reflex. Explain.

A

you cannot block this reflex unless there is severe brain damage

31
Q

Very high yield, is to understand the circuit for voluntary horizontal parallel eye movement as illustrated.

Note the contralateral cortical control of the frontal eye fields.

Note there are 4 important lesion sites that are shown and discussed on the next 5 pages.

A

????

32
Q

The vestibular output to the spinal cord arises from what two nuclei?

A

medial and lateral vestibular nucleus

33
Q

What is the difference between the projections from the medial and lateral vestibular nucleus?

A

MEDIAL vestibular nucleus gives rise to the medial vestibulospinal tract, which is a continuation of the MLF caudal to the abducens nucleus

  • the medial vestibulospinal tract, this pathway goes all the way to the neck muscles that cause rotation of the neck either to the left or right
  • the projection BILATERAL (these axons are traveling in the descending part of the MLF = the part of the MLF that you can follow caudal to CN VI)
  • excitation of this pathway causes extension of the neck
  • it is involved in vestibulo-cervical reflexes

LATERAL vestibular nucleus gives rise to the lateral vestibulospinal tract which is an IPSILATERAL projection

  • extends the length of the spinal cord whereas the medial vestibulospinal tract is projecting to cervical levels (Can’t follow it down to thoracic)
  • provides excitatory input to the extensors of the vertebral columns, and extensors of both limbs, anti-gravity muscles
  • involved in vestibulospinal reflexes
34
Q

Describe the medial vestibulospinal tract.

A

in the ventral (anterior) funiculus

  • originates from the medial vestibular nucleus
  • terminates medially in the ventral horn of the cervical regions
  • affects axial musculature (extensors of the neck)
35
Q

Describe the lateral vestibulospinal tract.

A
  • lies in the anterolateral side of the spinal cord
  • originates from the lateral vestibular nucleus
  • terminates in the intermediate, ventral horn of the spinal cord
  • promotes balance and the ability to stand with an erect posture
  • provides excitatory input to anti-gravity muscles such as extensors of the limb and the vertebral column
36
Q

What is the significance of these descending vestibulospinal pathways?

A

?????

34:00

37
Q

When discussing any pathway what is true?

A

there’s a topography; there is an organized way in which information is relayed to the nucleus to cortex

38
Q

The auditor pathways are tonotopically organized from the cochlea to the cortex. Explain.

A

in the vestibular nerve you can identify different parts of the vestibular nerve where different frequencies are found

39
Q

Unlike the visual

A

there are multiple, parallel auditory pathways to the cortex

40
Q

Unlike the somatosensory and visual system where you have first order, second order, third order neurons, the auditory system consists of what?

A

there are multiple, parallel auditory pathways to the cortex

-there are many ways in which auditory information gets to the cortex

41
Q

Why is recognition that the auditory system has multiple parallel pathway clinically significant?

A

lesion location

42
Q

If you have a lesion in the brainstem or in the pathway from the second order neurons to the cortex, will you get deafness?

A

you will NOT get monaural deafness (where you get deafness in one ear and the other ear is completely fine)

-this is due to the multiple pathways that send auditory
information to the cortex

-you will however loose some auditory functions for example the localization of sound

43
Q

How can you get partial deafness in one ear?

A

damage to the auditory cochlea, auditory portion of CN VIII, or the cochlear nuclei in the brainstem

44
Q

Describe the simplified version of taking auditory information to the primary auditory cortex.

A
  • We start in the cochlear that has first order neurons (bipolar) in the spiral ganglion.
  • Those send info to the second order neurons found in the dorsal cochlear nucleus in the brainstem.
  • those axons decussates and ASCEND to the third order neurons in the central nucleus of the inferior colliculus
  • those axons project to neurons in the medial geniculate nucleus (auditory)
  • those send auditory information (axons) through the internal capsule to auditory cortex (transverse gyrus of Heschl = area 41/42)
45
Q

Where do axons of the second order neurons in the dorsal cochlear nucleus decussate and what do they form?

A

in trapezoid body forming the lateral lemniscus

46
Q

T/F. The second order neurons of the auditory pathway decussate to the thalamus.

A

False, they decussate and form the lateral lemniscus which go to the inferior colliculus

47
Q

Different/various frequencies is faithfully relayed from the dorsal cochlear nucleus all the way to the cortex. Explain.

A

These auditory information carrying different sound frequencies are never intermixed. They are found separated from each other in specific parts of the cochlear nuclei, inferior colliculus, and medial geniculate nucleus.

SO the pathway is tonotopic.

48
Q

The auditory portion of CN VIII will terminate into what two nuclei, located where and supplied by what?

A
  • dorsal and ventral cochlear nucleus
  • located at the pontomedullary junction
  • supplied by AICA (anterior inferior cerebellar artery)
49
Q

If there is blockage, stroke of the anterior inferior cerebellar artery, what structures will be affected and thus what functions will be affected?

A
  • the dorsal and ventral cochlear nuclei
  • you will get monaural deafness (lose hearing in one ear)
  • So if you get a clinical case where the the patient has lost hearing in one ear you know AICA has to be involved or there is a lesion near the pontomedullary junction.
50
Q

What is the difference between the dorsal and ventral cochlear nucleus?

A
  • dorsal cochlear nucleus is located on the floor of the 4th ventricle and projects mostly CONTRALATERALLY; for pattern recognition of sound
  • ventral cochlear nucleus is located where CN VIII comes into the brain; projects mostly BILATERALLY (to the left and right)
51
Q

If there is a lesion across the ventral cochlear nucleus, what happens?

A

you will not have a loss of hearing because of the bilateral nature of the projection

52
Q

What nerves are found at the pontomedullary junction? If there is a loss of hearing, what other symptoms may be included? What arteries are involved?

A
  • CN VII and CN VIII
  • symptoms other than hearing loss may include those that deal with CN VII
  • AICA which comes off of the basilar artery; PICA comes off of the vertebral artery
53
Q

Axons of the lateral lemniscus terminate where?

A

inferior colliculus

54
Q

Brainstorm reminders

A
  • medial lemniscus dealing with fine touch
  • immediately lateral to that is the spinothalamic tract
  • lateral lemniscus is superior lateral to the medial lemniscus
55
Q

What is the ridge going between the inferior colliculus and the medial geniculate nucleus in the gross brainstem?

A

the brachium (arm) of the inferior colliculi

56
Q

What is the back of the thalamus called?

A

pulvinar

57
Q

What fissure separates the temporal lobe from the frontal and parietal lobe? What is located inside this fissure?

A
  • lateral fissure

- transverse gyrus of Heschl (the primary auditory cortex AKA area 41 and 42)

58
Q

What is the planum temporale?

A
  • the secondary auditory cortex
  • it is the cortex deep and hidden to transverse gyrus of Heschl AKA area 41 and 42
  • larger on the left (if you left dominance of brain)
  • forms the core of Wernicke’s area (recognizes sound and words as speech)
  • area for music (perfect pitch)
  • area for sound localization
59
Q

Functional Characteristics of Primary Auditory Cortex

A
  • Tonotopic organization but frequency selectivity is wide
  • Localization, including a few in the median plane

•Some cells fire only when there is an auditory and visual
stimulus with the same receptive fields

•Some neurons fire only to tones, others only to noise

•Some fire only to a sound complex (patterning of auditory
stimuli)

•Some cells sensitive to frequency modulation (changes in the
frequency of a sound), and some only to ascending, others only
to descending changes, and others only to the rate of frequency
modulation.

60
Q

How do you localize sound?

A
  • it depends on the frequency
  • low frequency sounds (<3 kHz) are coded by interaural time difference
  • high frequency sounds (>3 kHz)are coded by interaural intensity differences

depending on how loud the sound is on the left and right relative to each other, the nervous system can tell the difference; the intensity difference helps us to localize sound

61
Q

Most of the sound localization will be in what nucleus?

A

ventral cochlear nucleus which projects BILATERALLY and goes through the superior olivary nucleus

dorsal cochlear nucleus is more so pattern recognition

62
Q

Any auditory signal that goes from left to right the place of decussation to the auditory system is?

A

trapezoid body

63
Q

What is the common auditory pathway for pattern recognition as well as sound localization?

A

lateral lemniscus

64
Q

How do I know if I am looking at a caudal pons cross section?

A
  • you will see abducens nucleus with the facial nerve looping around it
  • medial lemniscus
  • trapezoid body where both the ventral and dorsal cochlear nuclei cross to the other side
65
Q

What nucleus is important for sound localization besides the ventral cochlear nucleus?

A

superior olivary nucleus

after decussation at the trapezoid body the axons of the ventral cochlear nucleus will synapse in the superior olivary nucleus BILATERALLY!!!

those axons will then project to the inferior colliculus via the lateral lemniscus

66
Q

What is important about the superior olivary nucleus besides sound localization?

A

it directly inhibits the cochlea spiral ganglion so it can modulate the neuronal activity coming out through the auditory nerve (this is important in terms of reducing background sound)

  1. sends bilateral inhibitory efferents to cochlea
  2. form olivocochlear fibers (to hair cells)
  3. reduces background noise
67
Q

What is an auditory evoked potential?

A

it is essentially an EEG where you put gross electrodes on the scalp

with the evoked potentials the difference is when you’re recording brain electrical activity, you’re recording these brain waves to a stimulus

you can get a characteristic evoked potential map and compare with a patient (for example a 3’s amplitude is not as high)

The test is also called a brainstem auditory evoked potentials (BAEP) or auditory brainstem response (ABR) test. A BAER test can help to diagnose hearing loss and nervous system disorders, especially in newborns, young children, and others who may not be able to participate in a standard hearing test.

Chika- SF2 (63 decks)

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