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CN VIII Flashcards

1
Q

Branches of vestibulochoclear n

A

Cochlear - hearing and detection of sound waves

Vestibular - sensation, head position relative to space and head movements relative to the body

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2
Q

CN VIII path

A

Exits brainstem at pontomedullary junction

  • subarachnoid space to enter internal auditory meatus
  • w/ NC VII in auditory canal through temporal bone
  • enter cochlear and vestibular organs
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3
Q

Hearing and vestibular sensations come from

A

Structures contained in inner ear

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4
Q

Inner ear

A

Semicircular canals
Vestibule
Cochlear

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5
Q

Bony labyrinth

A

Filled with perilymph

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6
Q

Membranous labyrinth

A

Filled with endolymph

  • semicircular canals
  • utricle and saccule
  • cochlear duct
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7
Q

Cochlea

A

Contains

  • Scalia vestibule (superior chamber of perilymph)
  • Scalia tympani (inferior chamber)
  • cochlear duct b/n them
  • basilar membrane b/n cochlear duct and Scalia tympani (extends entire width of cochlea)
  • organ of corti (in cochlear duct, residing on basilar membrane - hair cells, tectorial membrane, terminals of cochlear nerve)
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8
Q

Converting sounds to neural signals

A
  • sound waves hip tympanic membrane —> vibration of ossicles
  • vibration of oval window (Scalia vestibule) —> move perilymph
  • vibration of basilar membrane —> hair cells move
  • hair cell movement stimulates cochlear nerve
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9
Q

Hair cells and frequency

A

Higher frequency sound activate cells closer to oval window

Lower frequency activate closer to apex of cochlea

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10
Q

Axons of CN VIII travel to the dorsal and ventral cochlear nuclei

A

Fibers from both nuclei cross over via trapezioid body (ventral cochlear synapse bilaterally in superior oligarchs nuclei)
Ascend in lateral leminiscus to inferior colliculus
Fibers cross and ascend in brachium of inferior colliculus to MGN

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11
Q

Information from one ear ascends

A

Bilaterally which is why you get info on both sides of your brain from one ear

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12
Q

Small CNS lesions (CN VIII)

A

Rarely cause unilateral loss of hearing because auditory info projects bilaterally in brainstem and cerebrum

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13
Q

Primary auditory cortex

A

Conscious awareness of intensity of sound

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14
Q

Auditory association cortex

A

Compares sounds with memories of other sounds and classifies sounds (Area 42) (as language, music, noise, etc.)

Wernicke’s area (Area 22)- language comprehension

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15
Q

Unilateral hearing loss - damage to

A 
Damage to external auditory canal
middle ear
cochlear
organ of corti
Cochlear nerve
Cochlear nuclei
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16
Q

Unilateral hearing loss

A

Interferes w/ ability to locate sounds because timing of auditory info from each ear is combated to locate sounds

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17
Q

Conductive hearing loss

A

Caused by abnormalities in outer or middle ear

-wax buildup, otitis media, tympainic membrane tear

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18
Q

Sensorineural hearing loss

A

Disorders of cochlear or CN VIII

Prolonged exposure to loud noise, onto toxic drugs, Menderes disease, acoustic neuroma

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19
Q

Basic hearing can be tested with

A

Different frequencies

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20
Q

Conductive and sensorineural hearing loss can be tested

A

using tuning fork w/ rinne or Weber test

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21
Q

Acoustic neuroma

A

Compress CN III where it enteres auditory meatus

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22
Q

Tumor at cerebellopontine angle

A 
Most common cause of acoustic neuroma
-almost always unilateral 
-slow, progressive unilateral hearing loss w/ c/o tinnitus and balance problems
-mean age of onset is 50yo
Can include CN VII and CN V 
Removed surgically
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23
Q

Vestibular sensation

A

Structures in inner ear

24
Q

Vestibular apparatus

A

Semicircular canals and vestibule

Bone labyrinth w/ perilymph and membranous labyrinth w/ endolymph

25
Vestibular -membranous labyrinth
Utricle (openings to semicircular canal) And saccule Semicircular canal - small openings at each end to utricle
26
Vestibular - semicircular canals
Detect angular rotation of head (speed up or slow down rotation of head) Canals are perpendicular to each other
27
Three pairs of semicircular canals
Right and left anterior (45 deg ant to frontal plane) Right and left posterior (45 deg pst to frontal plane) Right and left horizontal (30 deg above horizontal plane)
28
Semicircular Calais work together as coplanar pairs
RP and LA RA and LP R and L horizontal
29
Ampulla
Bulge located at one of each semicircular canal Hair cells in crystal ampullaris have cilia Cilia of hair cells project up to cupula Movement of endolymph causes cupula to bend -results in deflection of cilia causing excitation or inhibitition of hair cells
30
Hair cells convert displacement
Due to angular head rotation into neural firing and send axons into the vestibular nerve
31
Each semicircular canal responds best
To motion in its own plane (w/ coplanar pairs responding to a shared plane)
32
brain detects direction of head movement by comparing
input from coplanar pairs When angular motion occurs w/in shared plane, each of the pairs produces reciprocal signals - excitatory from one w/ inhibitory from other. Results in neural firing that will increase in one vestibular nerve and decrease in another
33
During ipsilateral head rotations
Ipsilateral afferents are excited
34
Otolith organ
Vestibular pathway Calcium carbonate crystals embedded in top of gelatinous layer to give mass (shearing force w/ movement) Respond to linear motion and static head tilt w/ respect to the gravitational axis
35
Utricle
Vestibular pathways | Excitation occurs during horizontal linear motion and head tilt
36
Saccule
Excitation occurs during vertical linear motion
37
Macula
In utricle and saccule Contain hair cells in gelatinous layer Linear motion and head tilt cause otoconia to move and then gelatinous layer and hair cells move
38
Hair cells convert
Displacement into neural firing and send axons into the vestibular nerve
39
Vestibular nuclei
Have many connect w/ cerebrum, brainstem, motor systems, extraocular systems Sends awareness of head position to parietal association cortex that is integrated w/ visual and tactile information to contribute to spatial awareness
40
Vestibular nuclei adjust
Posture Muscle tone Eye position in response to movement of head in space
41
Vestibular nuclei integrate
Information from multiple senses, acting as central processor -primary processor of vestibular info Assist w/ refining movement (numerous connection w/ cerebellum)
42
Vestibular nuclie also receive
Visual Proprioceptive Tactile Auditory info
43
Vestibular nuclei lye
On lateral floor of 4th ventricle in pons and rostrum medulla
44
Four vestibular nuclei
Lateral Medial Superior Inferior
45
Lateral vestibular nucleus
Gives rise to lateral vestibulospinal tract Extends entire length of cord *maintaining balance and extensor tone
46
Medial vestibular nucleus
Largest Gives rise to medial vestibulospinal tract (medial motor systems) Extends to C spine *controlling head and neck position
47
Medial longitudinal fasciculus
Connect vestibular nuclei to oculomotor, trochlear and abducens nuclei Fibers mainly from superior vestibular nucleus and inferior (ascends in MFL to CN III, IV, VI
48
MLF function
Match eye movements resulting in conjugate gaze in all directions Pathway mediates the vestibulo-ocular reflex in which eye movements are adjusted for changes in head position
49
Vestibular info is sent mainly to
Flocculonodular lobes and vermis in cerebellum Vestibulocerebellum
50
Vestibular nuclei also send info to
1. Lateral temporal junction and posterior insula - conscious perception of head position and movement 2. CN XI nucleus - influence head position 3. Reticular formation - influence reticulospinal (posture and gait) tracts and autonomic centers for nausea and vomiting
51
Vertigo
Spinning sensation of movement Suggestive of vestibular disease more than any other sensations Most often from peripheral vestibular disorders (inner ear structures - CN VIII, SCCs, otolith)
52
Vertigo - lesions
Anywhere along the vestibular pathway from labyrinth, CN VIII, vestibular nuclei, cerebellum, cortex
53
Peripheral vestibular disorders w/ vertigo often accompanied by
Disequilibrium Nystagmus Nausea Vomiting
54
Benign paroxysmal positional vertigo (BPPV)
Sudden changes in head position resulting in vertigo and nystagmus Otoconia from nearby masculine dislodge and flat into a SCC - trauma or virus - at rest, otoconia settle in gravity dependent position in SCC - head moved quickly - otoconia move into new position in SCC causing abnormal movement of endolymph - causing abnormal signals in CV III *acute onset of vertigo and nystagmus
55
BPPV test and tax
Test w/ dix hallpike maneuver (PT rapidly but gently turns head so that one ear is down) Treated w/ repositioning maneuvers
56
Vestibular neuritis
Inflammation of vestibular nerve Virus Several days of intense vertigo, disequilibrium, nystagmus, nausea, symptoms subsiding over a few weeks Meds during acute phase my suppress vertigo and N/V
57
Ménière’s disease
Endolymphatic hydrops - excessive fluid and pressure in endolymph - recurrent intense vertigo along w/ fullness in ear w/ fluctuating hearing loss and tinnitus and N/V - meds during acute phase may suppress vertigo and N/V, w/ extreme cases vestibular nerve may be severed to relieve symptoms

Neuro Anatomy (22 decks)

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