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Vestibular System and Cerebellum Flashcards

1
Q

What are the 3 functions of the vestibular system?

A
  1. Mediate awareness of movement
  2. Adjust posture relative to position of head
  3. Generate eye movements that compensate for head movements
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2
Q

What afferents and efferents mediate our awareness of movement in the vestibular system.

A

–Afferents from CN VIII
–Efferents to the thalamus, to cortex

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3
Q

What efferents and afferents are involved in the vestibular system’s capacity to adjust posture relative to position of the head?

A

–Afferents from CN VIII
–Efferents to the cerebellum

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4
Q

What are the efferents and afferents that are responsible for the ability to generate eye movements that compensate for head movements?

A

–Afferents from CN VIII
–Efferents to reticular formation, cranial nerve nuclei controlling extraocular muscles

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5
Q

Inside the temporal bone, there is a bony/osseous labyrinth. What type of lymph is found here?

A

Perilymph

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6
Q

Within the bony labyrinth of the temporal bone is the membranous labyrinth which contains sensory organs bathed in what?

Describe the Na+ and K+ levels of this.

A

Endolymph

Has low Na+ and High K+

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7
Q

Meniere’s disease is characterised by vertigo, tinnitis and hearing loss. What is this caused by?

A

Defective circulation or absorption of endolymph

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8
Q

There are kinetic and static labyrinths, what is the kinetic labyrinth responsible for?

What are the organs of this labyrinth?

A

Responds to head movement, specifically angular velocity, movements like shaking head yes/no.

Semicircular canals, with ampullae and cristae

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9
Q

The static labyrinth responds to changes in head position and linear velocity.

What are two examples, of how this comes into play?

What are the associated organs?

A

Riding elevator and walking.

Vestibule: Utricle, saccule, maculae

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10
Q

What is the orientation of the kinetic labyrinth ducts?

A

Each side of the head has 3 paired semicircular canals - orthogonal orientation implies pairing.

Each lateral duct works in concert with the opposite lateral duct.

Superior duct works in concert with posterior duct on contralateral side.

Superior, lateral and posterior ducts work in y, x and z directions.

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11
Q

What is the relative position of ampullae in regards to the semicircular canals and the utricle?

A

Ampullae are tethered to the end of each of their respective semicircular canals by vestibular ganglions. Ampullae fall between semicircular canals and the utricle. See slide 10, Vestibular system lecture for visualization.

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12
Q

What are the cristae? What important aspect of the vestibular system do they contain?

A

A crista is a ridge of tissue that sits in the ampulla (enlargement of semicircular canal before the utricle). Cristae contain sensory hair cells and support cells.

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13
Q

What is a cupula? How does it relate to crista, hair cells, and ampulla?

A

A cupula is a gelatinous mass holding the cilia of the hair cells of the crista. The cupula sits in the ampulla of the semicircular cells.

Hair cells sit the crista, and synapse on the nerve. Nerve crosses utricle back to ganglion.

The crista sits on the cupula.

The cupula sits in the ampulla.

The ampulla sits in an enlargement of the semicircular canals, between the canals and the utricle.

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14
Q

What kinds of cilia do vestibular hair cells contain? How are they arranged?

A

All vestibular hair cells contain:

  1. Stereocilia - many
  2. Kinocilium

Stereocilia are arranged shortest to tallest, leading up to the kinocilium, which is the tallest cilia.

All kinocilia in a given crista are arranged in the same direction.

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15
Q

What does deflection of cilia in hair cells towards the kinocilium create? Away from the kinocilium? How does this work?

A

Deflection of the stereocilia towards the kinocilium creates a depolarization. Deflection of the stereocilia away from the kinocilium creates a hyperpolarization.

Mechanism works via stereocilia being linked to each other and the kinocilium with tip links. Tip link will have a K+ ion channel, and will be pulled open with deflection of stereocilia towards kinocilium.

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16
Q

Which cilia on hair cells synapses on the local vestibular nerve fiber?

A

Only the kinocilium synapses onto the nerve fiber. Nerve fibers eventually feed back onto vestibular ganglion.

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17
Q

What is the name for the type of transduction that hair cells do?

A

Mechanotransduction

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18
Q

How does the extracellular environment around hair cells allow them to create a tip-linked depolarization?

A

Depolarization of hair cells via tip links is dependent upon an influx of K+.

Hair cells are surrounded by endolymph, which is high in K+ and low in Na+. Opening of ion channels via tip links allows K+ to flow into cell, creating a depolarization.

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19
Q

How does angular velocity affect the endolymph, cupula, and stereocilia?

A

Angular movement of the head shifts endolymph in semicircular canals

Pressure from endolymph moves the cupula, as they are the same density.

Overall, results in movement and stimulation of stereocilia.

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20
Q

How do stereocilia deflect in response to angular velocity? What affects movement of endolymph itself (think general physics)?

A

Stereocilia generally deflect in the opposite direction of vector of velocity.

This is due to inertia.

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21
Q

What molecules move during the transduction process in inner ear hair cells?

A

Cupola deflection happens

Stereocilia and kinocilium all tilt in same direction

High K+ in endolymph causes influx (remember, typical AP is due to Na+ influx)

Ca++ influx happens, causes release of NT glutamate

Glutamate released from hair cells onto vestibular nerve fiber

Ribbon synapses are sued for massive release

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22
Q

What is so special about ribbon synapses? Where are they?

A

Ribbon synapses lie between hair cells and vestibular nerve fibers.

Ribbon synapses don’t need an AP (action potential) to fire. Instead, they release NT in proportion to the amount of glu released by the hair cell. Ribbon synapses are capable of responding to massive amounts of glu.

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23
Q

How is cilia movement facilitated by cupular displacement in different cristae in the kinetic labyrinths?

A

Kinetic Labyrinths:

Lateral cristae - cupular displacement towards utricle

Superior and posterior cristae - cupular displacement away from the utricle

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24
Q

What can activate the medial longitudinal fasciculus?

A

MLF is activated by lateral movement of the head

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25
Which way do eyes move with the vestibular ocular reflex (VOR)?
Eyes move opposite of head movement, i.e. head moves right and eyes move left. VOR can also affect gaze in up/down direction, using different cranial nuclei and extra-ocular muscles (EOmm).
26
What CN ganglion provides input into the MLF and VOR? What kind of neurons are in this ganglion?
Pseudounipolar neurons in vestibular ganglion, vestibular part of CN VIII
27
What is the path of the VOR in regards to eye movements with lateral movement? (Remember, path will differ with different head movements.)
Input into pseudounipolar neurons in vestibular ganglion First synapse onto vestibular nuclei Vestibular nuclei decussates and fires on PPRF (ParaPontine Reticular Formation) PPRF will send a neuron to fire on ipsilateral abducens nuclei (CN VI) - ipsi lateral rectus mm engaged PPRF will send another neuron that immediately decussates and travels up to contralateral oculomotor nucleus (CN III) via the MLF - contralateral medial rectus mm engaged
28
What will happen with a lesion to the left abducens nucleus?
Left eye won't turn forward and might drift medially when head is turned to the right
29
What also travels through the MLF?
Medial vestibulospinal pathway Medial carries information from medial vestibular nuclei for head position stability to bilateral mm
30
What EOmm does CN III innervate?
Superior rectus Inferior rectus Medial rectus Inferior oblique
31
What EOmm does trochlear nerve innervate?
Superior oblique
32
What EOmm does abducens innervate?
Lateral rectus
33
What does a lesion to CN III result in?
Eye cannot move up, down, and up & out
34
What does a lesion in CN IV result in?
Eye can't move down and out
35
What does a lesion in CN VI result in?
Eye cannot move laterally
36
What connects the nuclei for all the EOmm together?
MLF - connects CN nuclei for III, IV and VI
37
What clinical test will test the vestibulo-ocular reflex? How does it work? What is the name for the eye movements that result
Caloric reflex test - creates caloric nystagmus Cold water into ear canal will cause eyes to move towards stimulus Warm water into ear canal will cause eyes to move away from stimulus Test works by utilizing convection/heat transfer to change currents of the endolymph in semicircular canals, which will cause different stimuli to be sent to the vestibular ganglion.
38
What type of information is carried in the MLF of the VOR?
Vestibular information, equilibrium of head in space
39
What is the point of origin/primary cell body and receptors involved in the ascending portion of the MLF of VOR?
Origin/primary cell body - vestibular nerve fiber going into pseudounipolar neurons in vestibular/Scarpa's ganglion Receptors - ribbon receptors
40
Where is the first synapse in the ascending portion of the VOR of the MLF?
Vestibular ganglion neuron synapses onto vestibular nucleus in medulla - home of 2nd neuron
41
Where does the ascending portion of the VOR of the MLF travel?
After synapsing onto 2nd neuron in vestibular nuclei, 2nd neuron: decussates and heads up to pons, synapses onto PPRF in pons PPRF will send out 2 neurons: 1 - will synapse onto CN VI nucleus ipsilateral to the PPRF - will innervate ipsi lateral rectus 2 - will decussate into contralateral MLF, ascends to midbrain to go to contralateral CN III nucleus - will innervate contra CN III EOmm
42
Where does the ascending portion of the VOR of the MLF decussate?
Decussates twice: 1 - 2nd neuron from vestibular nucleus in medulla will decussate before pons 2 - 4th neuron from CN VI nucleus in pons will decussate before traveling to CN III in midbrain with MLF
43
Where does the descending aspect of the VOR of the MLF travel to?
Neurons from medial vestibular nucleus in medulla will bilaterally descend spinal cord and activate neck muscles - helps to stabilize the head - travels in medial longitudinal fasciculus, with medial vestibulospinal tract
44
What is nystagmus?
Rhythmic, involuntary eye movements - different velocities - can frequently 'overshoot' a bit and eye will quickly track back
45
What is the vestibulo-ocular reflex?
Nystagmus used to compensate eye position during head movement
46
What is the optokinetic reflex?
Nystagmus during movement of visual stimuli across retina - tracking of objects moving across field of vision during driving, running
47
What is saccades? Where does it originate from in the brain?
Rapid voluntary eye movements to move image into fovea Originates from superior colliculus (To remember: think of a hetero middle school boy confronted by a pair or breasts.)
48
Is nystagmus slow or fast?
Fast and slow phases are involved
49
What is "doll's head" nystagmus? What structures in the brain control it? What is it useful for?
Moving head of an unconscious person will elicit nystagmus followed by fast, jerky movements in the opposite direction. Nystagmus - from MLF (pons) Jerky contralateral movement - from superior colliculus (midbrain) Can use to localize suspected damage to brainstem - missing component indicates level damage is at
50
What afferent signals into the vestibular system is responsible for generating eye movements that compensate for head movements? Efferent signals?
Afferents - from CN VIII Efferents - go to reticular formation, CN nuclei for EOmm - III, IV and VI
51
What structures are an important part of the static labyrinth?
Utricle - enlargement of bony canal Saccule Maculae - similar to cristae
52
What is the macula?
Patch of support and hair cells in saccule and utricular walls
53
What is the orientation of the 2 maculae? What features do they have that make their hair cells responsive to movement?
Saccular macula is vertical Utricular macula is horizontal Maculae have otoconia - CaCO3 'sand' that lies on top of a membrane that overlies hair cell. Displacement of otoconia causes hair cells to depolarize or hyperpolarize. Just like hair cells in kinetic labyrinth, movement of stereocilia towards kinocilium = depolarization. Away = hyperpolarization.
54
When do otoconia displace hair cells?
During vertical or horizontal acceleration Saccules - vertical acceleration utricle - horizontal acceleration Hair cells in each utricle and saccule are arranged as mirror images of each other.
55
How is directionality conferred within the static labyrinths?
Conferred by which hair cells are specifically depolarized in the macula Striola is mirror image point, a groove within the macula. Sacculus hair cells (for vertical g's) are arrayed outward, pointing anterior and posterior Utricle hair cells (for horizontal g's) are arrayed inward, pointing medial and posterior
56
What happens to your static and kinetic labyrinth systems when you trip?
Static systems - fire onto lateral vestibular nucleus in mid-pons Nucleus then has neurons that descend via ipsilateral lateral vestibulospinal tract to ventral horn to mm of legs and posture, or anti-gravity extensor mm, to walk upright. Kinetic systems - fire onto medial vestibular nucleus in rostral medulla, which descends bilaterally down spinal cord in MLF and medial vestibulospinal tract to mm of neck and thorax - pulls head back to avoid faceplanting when falling. Can also innervate riMLF to train eyes on ground.
57
How does the VOR affect gaze in the upward/downward direction?
Output from vestibular ganglion synapse onto contralateral PPRF PPRF neurons will travel up to CN III to affect superior rectus and inferior oblique to move gaze in down or up direction
58
Where does the vestibulocerebellar tract take information?
Takes information from vestibular input into cerebellum for processing Takes information direct from Scarpa's ganglion, or from medial or inferior vestibular nuclei Info is then taken to inferior cerebellar peduncle then into flocculus of cerebellum
59
What components make up the inferior cerebellar peduncle? What tracts travel through here?
Inferior Cerebellar Peduncle = Juxtarestiform body + restiform body Vestibulocerebellar tract - where head is in space, ipsi Dorsal spinocerebellar tract - fine proprioception from lower body, ipsi Ventral spinocerebellar tract - gross proprioception from lower body, ipsi Trigeminocerebellar tracts - proprioception of face, ipsi Olivocerebellar tracts - tonic activity for motor memory, ipsi Efferents to vestibular nuclei
60
What circuits associated with the vestibular system adjusts posture relative to position of head?
Afferents from CN VIII Efferents to cerebellum
61
Where is conscious awareness of movement processed? How is relayed from the brainstem to the cortex?
Lateral and medial vestibular nuclei have bilateral projections to the VPM of the thalamus From VPM there is bilateral projection to primary sensory cortex and superior parietal lobule (which has conscious awareness of being off-balance, and conscious awareness of equilibrium of limb.)
62
What associated structures of the vestibular system mediates awareness of movement?
Afferents from CN VIII Efferents to thalamus, cortex
63
What is vertigo? What are 2 common causes?
Vertigo = illusions of movement EtOH - makes cupula change density, can have movement of cupula without endolymph movement Aging/trauma - detachment of otoconia to semicircular duct, pushes cupula
64
What is PICA/Lateral Medullay/Wallenburg's Syndrome? What are the symptoms?
Lesion of part of vestibular nucleus, inferior cerevellar peduncle, spinal tract and nucleus of trigeminal nerve, nucleus ambiguus, and spinal lemniscus at level of rostral medulla. Caused by thrombosis of vertebral or PICA artery. Damage to vestibular nuclei = vertigo, inaccurate reachin, eyeballs deviate 10 degrees, head tilt to same side, fall towards same side
65
What are the systemic symptoms of Wallenburg syndrome?
Spinocerebellar fibers disrupted = cerebellar ataxia Sensory trigem damage = ipsilateral loss of nociception and thermosensitivity to face Ipsilateral sympathetic pathway = Horner's syndrome Nucleus ambiguus - hoarsenss and dysphagia Spinothalamic tract damage = contralateral loss of pain and temp in trunk and limbs
66
What causes Romberg's sign?
Defects in vestibular and somatosensory inputs to sense of orientation Stopping visual inputs into sense of orientation to test vestibular and somatosensory inputs.
67
What are the 4 functions of the cerebellum?
Planning movements Limb and postural adjustments Equilibrium and eye movements Motor learning
68
What defines the cerebellar lobes?
Fissures and longitudinal zones Posterior and posterolateral fissures Flocculonodular lobe across the inferior aspect Vermis down median Paravermis just lateral Lateral zones on the lateral-most aspects
69
What are the 3 functional divisions of the cerebellum? What are the relative ages in evolution of mammals? What are the associated lobes?
Vestibulocerebellum - "middle aged" - on flocculonodular node Spinocerebellum - "old"/paleocerebellum - on vermis and paravermal nodes Cerebrocerebellum - "new"/neocerebellum, on lateral zones
70
How many cerebellar peduncles are there?
3: superior, middle and inferior
71
What crosses through the middle cerebellar peduncle? Do these neurons decussate? What do these neurons become in the cerebellum?
Contralateral cortical input - corticopontocerebellar tracts Cortical information descends to pons to nucleus on ipsilateral side and synapse Fibers from pons nucleus decussate through pons into contralateral medulla and become mossy fibers
72
What does the superior cerebellar peduncle transmit? What is this a major pathway for?
Sup cerebellar peduncle = major output pathway for cerebellum Ventral spinocerebellar tracts - contralateral proprioceptive info from upper body Efferents: Contralateral red nucleus - goes to thumbs, because reasons VL nucleus in thalamus
73
What are the fiber types/order of cells in the cerebellar circuits? (review)
Mossy fibers --\> granule cell --\> bilateral parallel fibers --\> Purkinje cells
74
What happens to input neurons in the cerebellum? Do the cerebellar circuits remain segregated?
Cerebellar circuits form functional units with mixed-input connectivity Input sources = segregated mossy fibers = segregated granule cells = go in segregated, go out mixed parallel fibers = mixed purkinje cells = mixed See slide 55 for more info, schematics
75
What are the 5 types of cells found in the cerebellum? What do they do?
Granule cells - bilateral parallel fibers Purkinje cells - go to DCN or vestibular nuclei Stellate cells - get input from parallel fibers, inhibit purkinje cells, in molecular layer Basket cells - local inhibitory neurons on purkinje cells Golgi II cells - input from parallel fibers, inhibit granule cells
76
What are the layers of the cerebellar circuit, from superficial to deep?
Molecular layer Purkinje layer Granular layer
77
What cells do the layers of the cerebellum contain?
Molecular - parallel fibers, purkinje dendrites, stellate cells Purkinje - cell bodies of purkinje cells, basket cells Granule cell layer - densely populated layer containing granule cells, cell bodies of golgi cells
78
What 2 NTs define the basic cerebellar circuitry?
GABA and glutamate All cells are glutaminergic except for Purkinjes, which are GABA-ergic
79
What are climbing fibers in the cerebellum? Where do they come from, and what do they do?
Climbing fibers come directly from contralateral inferior olivary nucleus Glutaminergic neurons Synapse directly onto deep cerebellar nuclei and dendrites of Purkinje cells
80
What does the basic cerebellar circuit allow for?
Circuit allows for comparison of ongoing movement and sensory feedback derived from it Expectation from motor cortex Proprioception from spinocerebellar tracts to provide sensations of ongoing movement
81
What do olivary neurons do? How are they different from many other neurons? How do they travel to the cerebellum?
Olivary neurons provide tonic stimulation to the cerebellum These neurons use electrical synapses and gap junctions Travel from olivary nucleus, decussate immediately Go into contralateral inferior cerebellar peduncle, provide tonic oscillations via climbing factors Necessary for motor learning
82
What circuits are associated with motor learning in the cerebellum?
Afferents - CN VIII, inferior olivary nucleus Efferents - reticular formation, CN nuclei controlling EOmm
83
How are deep cerebellar nuclei arranged? What are the names for them?
Arranged in columns: Dentate - most lateral Interposed (globose and emboliform) - medial, most anterior Fastigial - medial, most posterior
84
What is the organization/path of vestibular input to the cerebellum? What movements does this affect?
Input through inferior peduncle as mossy fibers - axons direct from Scarpa's ganglia, or after 1st synapse in vestibular nuclei Go to flocculonodular lobe Go to fastigial nucleus Output to vestibular nuclei and reticular formation Affects eye movements and equilibrium
85
What symptoms does a lesion to the fastigial nucleus or flocculonodular lobe present as?
Inability to move eyes back and forth effectively
86
What is the organization/path of trunk and limb postural adjustments in the cerebellum? What motions does this affect?
Input through inferior peduncle as mossy fibers - input mostly from spinocerebellar tracts Input goes to vermis and paravermal region Then goes to fastigial nucleus and interposed nuclei Output goes to vestibular nuclei and reticular formation, ultimately to thalamus and cortex Motions affected - walking, posture, eye movements
87
How is cortical input organized/transmitted into the cerebellum? What motions does this affect?
Cortical input represents "processed" and coordinated info Input through MIDDLE peduncle as mossy fibers - from contralateral cerebropontocerebellar nuclei Travel to lateral zones and intermediate zones Travel to dentate and interposed nuclei Output to red nucleus and inferior olivary nucleus, also to VA/VL of thalamus Leaves via superior cerebellar peduncle Decussates again after leaving Affects planning and programming of voluntary movements, motor learning
88
What circuits are associated with planning movements in the cerebellum?
Afferents from contralateral premotor/supplementary motor cortex Efferents to thalamus, cortex
89
What is an intention tremor?
AKA Cerebellar Tremor Tremor that doesn't go away with intentional movement, and worsens near endpoint of intentionally guided movement. Frequently leads to dysmetria.
90
What is ataxia?
Lack of voluntary coordination of muscle movements Frequently a sign of cerebellar pathology
91
What is anterior lobe syndrome?
Caused by malnutrition from chronic alcoholism Affects the area around vermis Legs most strongly affected - broad, staggering gait with ataxia
92
What is neocerebellar syndrome?
More common in upper limbs Characterized by: Hypotonia Ataxia Dysmetria Intention tremor Dysdiadochokinesia
93

Neuro Exam II (13 decks)

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