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SF2_Exam3 > Auditory and Vestibule Pathways > Flashcards

Auditory and Vestibule Pathways Flashcards

1
Q

CN VIII enters the brain as 2 roots where?

A

At the junction of the pons and medulla

Pontomedullary junction

Medial root = vestibular root

Lateral root = auditory root

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2
Q

CN VIII exits the _______ cranial fossa and enters the _________ portion of the temporal bone via the _________.

A

Posterior Cranial Fossa

Petrous

Internal acoustic meatus

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3
Q

Schwannoma typically occur at which root of CN VIII

A

Vestibular part

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4
Q

What is in the petrous portion of the temporal lobe?

A

Labyrinth

Special organs of hearing and balance

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5
Q

CN VIII has 3 sensory ganglia containing bipolar neurons. What are they?

A

Spiral ganglion: bipolar neurons for hearing (in cochlea)

Inferior nad superior vestibular ganglia - bipolar nuerons that carry information from the vestibular portion

1st order neurons

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6
Q

The bipolar cells from the 2 vestibular ganglion project to?

A

Cerebllum (only sensory nerve in which it recieves direct afferents) and 4th vestibular nuclei (2nd order nueron)

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7
Q

The vestibular ganglion projections go to which two parts of the cerebellum?

A
  1. Flocculonodular lobe - oldest part of the cerebellum/balance and eye movement
  2. Vermis - central part of the cerebellum
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8
Q

What are the 4 vestibular nuclei?

A
  1. Lateral
  2. Medial
  3. Superior
  4. Inferior (descending)

Located in the rostral medulla/caudal pons (floor of the 4th ventricle around pontomedullary junction)

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9
Q

The Superior Vestibular nucleus is part of which tract?

A

Ipsilateral acending MLF

MLF interconnects the motor nuclei that control eye movement

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10
Q

The Medial Vestibular nucleus is part of which tract?

A

MLF and medial vestibulospinal tract

The medial vestibulospinal tract is a descending tract that controls movements for extension of the neck and head movement

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11
Q

The lateral vestibular nucleus is part of which tract?

A

Lateral Vestibulospinal tract

This a descending tract, contol excitation of antigravity muscles (what causes extension of our paraspinal muscles and limbs

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12
Q

Identify the nuclei in this image

A

Red: Superior Vestibular nucleus

Orange: Medial Vestibular nucleus

Green: lateral vestibular nucleus

Image slice form caudal pons

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13
Q

What are the vestibular outputs that essential control balance/gaze and posture?

A
  1. Extraocular motor nuclei via MLF (CN 3, 4, and 6)
  2. Cerebellum (reciprocal connection): recieve direct afferent and also second order input from vestibular nuclei
  3. Ventral posterior nucleus of thalamus - where the second order nuerons terminate (to post central gyrus )
  4. Reticular formation - forms the core of the medulla, pons, and the brain. Meshwork of connections
  5. Spinal Cord - spinal pathways
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14
Q

The extraocular motor nuclei via the MLF are involved in? Which two nuclei are involved?

A

Involved in horizantal gaze, lateral movements, and nystagmus

Medial vestibular nucleus and superior vestibular nucleus are involved

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15
Q

In this brainstem cut which cranial nerve is projecting to the MLF?

A

This is a image of the pons. CN VI is projecting to the MLF

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16
Q

In this brainstem cut which cranial nerve is projecting to the MLF?

A

This is a image of the midbrain

CN III is projecting to the MLF

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17
Q

Explain the VEstibulo-Ocular Reflex

A

Two neuron in the abducens nucleus. One is a motor that go to lateral rectus. There are a bunch of interneurons that receive the same input as the motor neurons. Interneurons will project to the oculomotor through the medial longitudinal fasciculus pathways

When the motor neurons of lateral rectus get engaged the motor neurons sitting right next door get excited and they project to the opposite side. The contralateral motor nucleus (MLF). So motor neuron controlling medial rectus get the same excitatory input.

This will cause the eyes to both look into the same direction (lateral gaze)

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18
Q

What are the steps involved in the Vestibulo-Ocular Reflex (VOR)?

A
  1. Endolymph flow stimulates hair cells (right)
  2. Increase nerve firing rate
  3. Simulates vestibular nuclei (projections to VI and III nuclei)
  4. Both eyes look left

Nystagmus (fast movement of the eye) occurs after the body realizes that the eyes are no longer looking forward.

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19
Q

When you turn your head to the left what happenes to the activity in the left vestibular nucleus?

A

It decreases

(eyes move in the opposite direction of increased activity)

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20
Q

Correction of eye gaze (Nystagmus) is done by what?

A

The cortex

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21
Q

What is Caloric Stimulation?

A

This test is performed on patients who are in coma to test their state of consciousness.

Warm Water (Right ear)

Increase firing in Right vestibular nucleus -> eyes look to the leff (opposite of stimulus) -> Nystagmus in the same direction of stimulus

Cold Water (Right Ear)

Decrease firising of Right Vestibular nucleas -> eyes move to the right (same direction as stimulus) -> Nystagmus to to the left (opposite of stimulus)

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22
Q

Lesion in the vestibular nuclei?

A

This is the same as having decrease firing of nucleus. Nystagmus will occur in the oppostie direction of the lesion

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23
Q

What is the purpose of the caloris test (Vestibulo-ocular reflex)?

A

To assess 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.

24
Q

Outputs of the vestibular nuclei to the spinal cord involve which two tracts?

A

Medial Vestibulospinal tract (descending MLF)

and

Lateral Vestibulospinal tract

25
Q

Medial Vestibulspinal tract

A

Continuation of the MLF caudal to the abducnes nucleus. Pathway goes all the way to the neck (cervical) muscles

a. medial vestibular nucleus (origin)
b. bilateral (via descending MLF)
c. extension of neck when excited (axial musculature)
d. vestibulo-cervical reflexes
e. terminates medially in the ventral horn of cervical regions (axial musculature/RExed Lamina 9)

26
Q

Lateral Vestibulospinal tract

A

Extends the length of the spinal cord

a. lateral vestibular nucleus (origin)
b. ipsilateral
c. antigravity muscles (balance, shoulder and elbow)/excitatory
d. vestibulo-spinal reflexes
e. terminates in the intermediate, ventral horn

27
Q

Overaction of the lateral vestibulospinal tract can lead to?

A

Decorticate and Decerebrate Rigidity

28
Q

What is Decerebrate Rigidty?

A

Mal-formed Posture, if you cut away descending motor input to the vestibular nuclei or over activation of the lateral vestibular nucleus and the medial vestibular nucleus

Notice that his neck is in extension. Upper limb and lower limb is ridged in extension. Rigidity occurs because the cortex provides inhibition to the vestibular nuclei. So when you remove cortex the nuclei don’t have inhibition so they become over active

29
Q

The first auditory neurons are located where?

A

At the spiral ganglion

(located in the middle of the cochlea

30
Q

Central Auditory Pathways

A
  • the auditory pathways are tonotopically organized from the cochlea to the cortex
  • there are multiple, parallel auditory pathways to the cortex
31
Q

Lesion at CN VII or the auditory nuclei can cause what?

A

Deafness

brainstem or cortical lesions after the cochlear nuclei will NOT produce monaural deafness

32
Q

How many neurons are involved in the Auditory pathways for Pattern Recognition?

A

4

33
Q

Describe the Auditory Pathway for Recognition

A
34
Q

Identify the parts of the pathway

A

A. Dorsal cochlear nucleus

B. CN VIII

C. Trapezoid body: decussation

D. LAteral lemniscus

E. Inferior colliculus

F. Transverse gyrus of Heshl (Area 41 and 42)

G. Medial Geniculate

35
Q

The auditory nerve axons synapse __________ on secondary neurons that are found in two cochlear nuclei.

A

Ipsilateral

36
Q

What are the two cochlear nuclei and where are they found?

A

Dorsal and Ventral nuclei located at the pontomedullary junction.

Supplied by AICA

37
Q

Ischemic stroke of the left Anterior inferior cerebral cortex causes whats?

A

Mono-deafness

Dorsal and Ventral nuclei lose their blood supply

38
Q

What is the funciton of the dorsal cochlear nucleus?

A

Pattern Recognition of sound

Project mostly contralaterally

39
Q

This nucleus projects bilaterally and if lesioned you will NOT have a lost of hearing.

A

Ventral Cochlear Nucleus

40
Q

What is circled in this image?

A

Trapezoid body

bundle of crossing fibers from the cohlear nuclei

41
Q

Identify the stuctures tages in this image

A

Red - Lateral Lemniscus

Yellow - Spinothalamic tract

White - medial lemniscus

42
Q

Identify the structures in this image

A

Inferior colliculus

White arrow is pointing at the lateral lemniscus

43
Q

Identify the structures in the image

A

Red circle - medial geniculate nucleus

Top yellow arrow = brachium of the inferior colliculus

Bottom yellow arrow = inferior colliculus

44
Q

Identify the structures in this image

A

A. Superior Colliculus

B. Inferior Colliculus

C. Brachium of the inferior Colliculus

D. LAteral Geniculate nucleus

E. Medial geniculate nucleus

45
Q

Identify the structure in the red circle

A

Medial Geniculate nucleus

46
Q

Area 41 and 42 represent what?

A

Primary Auditory Cortex

47
Q

What are the functional characterisitc of the 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.

48
Q

SLide 38

A

SLide 38

49
Q

What is the Planum Temporale?

A

Secondary Auditory Cortex located behind the transverse Gyrus

1. Larger on the left

2. Language (Wernicke’s )

3. Music (Perfect Pitch)

4. Sound localization

50
Q

The localization of sound is mapped where?

A

In the brainstem

1) Low frequencies (<3 kHz): interaural time differences
2) High frequencies (>3 kHz): interaural intensities differences

51
Q

Low Frequencies

A

detected in the anteroventral cochlea -> medial s. olivary (lateral-ipsi, medial cortex), coincidence detectors

52
Q

High frequencies

A

Detected in the anteroventral cochlea -> lateral s. olivary and medial trap. nucleus

53
Q

Sound localization mainly occurs where?

A

In the Ventral cochlear nucleus

(dorsal is more for oattern recognition)

54
Q

What are the inputs and outputs of the superior olivary nucleus?

A

Inputs: bilateral - ventral cochlear n.

outputs: inferior colliculus

Function:

Sends bilateral inhibitory efferents to cochlea

form olivocochlear fibers (to hair cells)

reduces background noise

55
Q

What is auditory Evoked Potential?

A

EEG: electrical activity/brain waves in response to activity

Characteristic potential of where auditory information is passing. Each beep represents another part of the auditory pathway

56
Q

If there is a distance difference in the Auditory Evokes potential chart, what does that indicate?

A

Demylination of an axon

57
Q

If there is a decrease in amplitude in Auditory Evoked potential, what does that indicate?

A

Nucleus or track lesion

SF2_Exam3 (14 decks)

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