Vestibular System and Cerebellum

Question 1

Primary function of cerebellum

Answer 1

Entirely (unconscious) motor function

Maintenance of equilibrium, posture, muscle tone, coordination

Question 2

Cerebellum is characterized by presence of deep fissures. Prominent fissures divide the cerebellum into ____ and _____.

The deep primary fissure separates the small _____ lobe from the ______ lobe.

The posterolateral fissure defines the _____ and _____

Answer 2

Lobes; lobules

Anterior;posterior

Flocculus; vermis (nodule)

Question 3

The flocculus of the cerebellum + nodule of vermis = __________ of cerebellum

Answer 3

Flocculonodular lobe

Question 4

Structures on cerebellum that are smaller creases made up of cortical ridges

Answer 4

Folia

Question 5

______ ______ = superifical cellular layer of each folium

Answer 5

Cerebellar cortex

Question 6

Layers of cerebellar cortex

Answer 6

Purkinje cell layer (sandwiched between granular layer)

Granular cell layer (immediately adjacent to white matter core)

Molecular layer (few cells but high # of processes)

Question 7

Which layer of the cerebellar cortex contains the only efferent neurons of the cerebellum?

Answer 7

Purkinje cell layer

Question 8

The granular cell layer of the cerebellar cortex contains excitatory neurons that synapse with _____ cells as well as ____ and ____ cells of the molecular layer

This layer also contains _____ cells which are inhibitory cells that extend dendrites into the molecular layer

Answer 8

Purkinje; basket; stellate

Golgi

Question 9

2 types of cells in molecular layer

Answer 9

Basket cells
Stellate cells

[inhibitory cells]

Question 10

___ ____ = core of myelinated fibers in cerebellum

Answer 10

Arbor vitae

Question 11

Cerebellum consists of 2 laterally located hemispheres joined in midline by _______

Answer 11

Vermis

Question 12

3 cerebellar peduncles:

Superior cerebellar peduncle = predominantly ______ fibers from cerebellar nuclei

Middle cerebellar peduncle = emerges laterally from basal _____; composed of ______ fibers to cerebellum from contralateral pontine nuclei

Inferior cerebellar peduncle = _____ fibers to cerebellum from spinal cord and brainstem

Answer 12

Efferent

Pons; afferent

Afferent

Question 13

Largest cerebellar peduncle

Answer 13

Middle

Question 14

Superior cerebellar peduncle is predominently efferent fibers from cerebellar nuclei which distribute where?

Answer 14

Diencephalon

Brainstem

Question 15

The inferior cerebellar peduncle is associated with the:

_____ ____ (wall of 4th ventricle): composed of reciprocal fibers b/w cerebellum and vestibular structures

______ _____: contains fibers arising in SC or medulla

Answer 15

Juxtarestiform body

Restiform body

Question 16

______ receive afferents from multiple regions and are the output/efferents of the cerebellum

Answer 16

Deep cerebellar nuclei

Question 17

What are the 3 deep cerebellar nuclei?

Answer 17

Dentate nucleus
Interposed nucleus (anterior emboliform + posterior globose)
Fastigial nucleus

Question 18

3 types of afferent fibers to cerebellar cortex

Answer 18

Mossy fibers
Climbing fibers
Multilayered (monoaminergic fibers)

Question 19

______ fibers are cerebellar afferent axons that originate from cerebellar nuclei and other nuclei in the SC, medulla, and pons

Answer 19

Mossy

Question 20

Mossy fibers branch profusely in ______ layer and contact other cells at irregular intervals, creating the _________

Answer 20

Granular; mossy fiber rosette

Question 21

Central element of mossy fibers, giving them their mossy appearance

Answer 21

Cerebellar glomerulus

Question 22

Mossy fibers are excitatory to _____cell and ____ cell dendrites

Answer 22

Granule; golgi

Question 23

Climbing fibers are afferent cerebellar fibers that arise from the _____ nuclei.

______ fibers send collaterals to appropriate cerebellar nucleus that corresponds to overlying cortical zone

Climbing fibers terminate in molecular layer by entwining up the dendritic trees of the ______ dendrites

Answer 23

Inferior olivary

Olivocerebellar

Purkinje

Question 24

Each purkinje cell is innervated by a single _____ fiber and they excite purkinje cells and cerebellar nuclear neurons on which their collaterals terminate

Answer 24

Climbing

Question 25

Multilayered (monoaminergic) fibers are cerebellar afferents associated with what 3 structures?

Answer 25

``` Locus ceruleus (noradrenergic) Raphe nuclei (serotoninergic) Hypothalamus ```

Question 26

Multilayered (monaminergic) fibers enter the cerebellum mainly via _____ _____ and may send collaterals to cerebellar nuclei. Axons branch diffusely and terminate in ____ and ____ layers, influencing all major cell types. They function in decreasing spontaneous discharge rates and altering responsiveness of ____ cells

Answer 26

Cerebellar peduncles Molecular; granular Purkinje

Question 27

3 functional subdivisions of cerebellum

Answer 27

Spinocerebellum (paleocerebellum) Vestibulocerebellum (archicerebellum) - oldest Pontocerebellum (neocerebellum)

Question 28

The spinocerebellum approximates to the ____ and surrounding area, with the _____ and ____ nuclei

Answer 28

Vermis; globose; emboliform

Question 29

Function of spinocerebellum

Answer 29

Muscle tone/posture

Question 30

Spinocerebellum controls muscle tone/posture via afferents from _____ and ______ tracts, with info from muscle, joint, and cutaneous receptors via ______ and _______ cerebellar peduncles

Answer 30

Spinocerebellar; cuneocerebellar; inferior; superior

Question 31

Spinocerebellum fibers terminate in cortex of ipsilateral _____ and adjacent ________

Answer 31

Vermis; paravermis

Question 32

Output of spinocerebellum is focused primarily on control of axial and limb musculature — what neural pathways are involved with each?

Answer 32

Axial: vermal cortex + fastigial efferents —> vestibular and reticular nuclei Limbs: globose + emboliform nuclei —> superior cerebellar peduncle —> red nucleus + thalamus

Question 33

The vestibulocerebellum is equated with the _____ lobe and _____ nuclei

Answer 33

Flocculonodular; fastigial

Question 34

Function of vestibulocerebellum

Answer 34

Maintenance of balance/equilibrium

Question 35

Vestibulocerebellum controls balance and equilibrium maintenance via connections with _____ and _____ nuclei of brainstem via inferior cerebellar peduncle. This info is relayed to the ipsilateral _____ lobe

Answer 35

Vestibular; reticular; flocculonodular

Question 36

Cortical efferent fibers of the vestibulocerebellum —> _______ nucleus ——> _______ nuclei + reticular formation LMN output is bilateral via _____ and _____ projections

Answer 36

Fastigial nucleus; vestibular Vestibulospinal; reticulospinal [note that a portion of fastigial efferents goes contralateral]

Question 37

The pontocerebellum makes up the majority of the cerebellar hemisphere and ____ nuclei

Answer 37

Dentate

Question 38

Function of pontocerebellum

Answer 38

Muscle coordination + speed/force/trajectory of movements

Question 39

Fibers of pontocerebellum are principle afferents that cross to the contralateral side of the brainstem and enter via ____ cerebellar peduncle They then terminate predominantly in lateral parts of _____ _____

Answer 39

Middle Cerebellar hemisphere

Question 40

Output from pontocerebellum is directed to the ____ nucleus. It projects to the contralateral ____ nucleus and ventral lateral nucleus of the ________ (via superior cerebellar peduncle). The VLN then projects to the motor cortex

Answer 40

Dentate; red; thalamus

Question 41

The action of the pontocerebellum on the cerebral cortical areas gives rise to descending _____ and _____ paths

Answer 41

Corticospinal; corticobulbar

Question 42

Results of lesions of lateral cerebellum

Answer 42

Dyssynergia (deterioration of coordinated movement) May also see hypotonia and decreased DTRs Extremity ataxia Unsteady gait + tendency to lean toward side of lesion

Question 43

Other nonspecific results of cerebellar lesions

Answer 43

Dysmetria = past-pointing (hypermetria vs. hypometria) Tremor = intention tremor, static tremor

Question 44

Difference between 2 primary vestibular receptor organs

Answer 44

Semicircular canals (horizontal, anterior, posterior) = detect rotational movements aka angular acceleration Otolith organs (utricle, saccule) = detect translational movement aka linear acceleration

Question 45

Receptor cells in vestibular receptor organs are innervated by primary afferent fibers of ______ ganglion Cell processes of these bipolar cells enter the brainstem and terminate in ipsilateral ________ nuclei and cerebellum

Answer 45

Vestibular (scarpa ganglion) Vestibular

Question 46

4 main vestibular nuclei and their locations

Answer 46

Superior vestibular nucleus (superolateral in central pons) Medial vestibular nucleus (lateral floor of 4th ventricle) Lateral vestibular nucleus (lateral to medial vestibular nucleus) Inferior vestibular nucleus (lateral to medial and inferior to lateral)

Question 47

The superior vestibular nucleus is bordered by the ____ body and ___ ventricle

Answer 47

Restiform; 4th

Question 48

Which vestibular nuclei contains large neurons known as Deiters cells?

Answer 48

Lateral vestibular nuclei

Question 49

Major targets of vestibular nuclei

Answer 49

``` Oculomotor nuclei Vestibulocerebellum Contralateral vestibular nuclei Spinal cord Reticular formation Thalamus ```

Question 50

Primary vestibular afferents enter brainstem at _____ junction and traverse the ____ body before bifurcating into asecnding and descending branches

Answer 50

Pontomedullary; restiform

Question 51

Afferent fibers from semicircular canals project to ___ and ______ vestibular nuclei Minor inputs reach the ____and _____ vestibular nuclei

Answer 51

Superior; medial Lateral; inferior

Question 52

Otolith organs project primary afferents to which vestibular nuclei?

Answer 52

Lateral Medial Inferior

Question 53

Saccular afferents project to neurons in the contralateral _____ nucleus which influences vertical eyemovements

Answer 53

Oculomotor

Question 54

Vestibular nuclei show directional selectivity for particular head movements due to: ____ and ____ vestibular nuclei receive info from otoliths and one semicircular canal pair ____ and _____ vestibular nuclei receive info from several canal pairs and otolith receptors

Answer 54

Superior; medial Lateral; inferior

Question 55

What network permits keeping a fixed gaze on an object while head is moving?

Answer 55

Vestibuloocular network (vestibuloocular reflex)

Question 56

The vestibuloocular reflex is characterized by primary afferents from horizontal semicircular canals that project to specific neurons in the medial and lateral vestibular nuclei Describe the path of these axons

Answer 56

Primary afferents send axons through MLF to contralateral abducens nucleus Abducens motor neurons send excitatory impulses via CN VI to ipsilateral lateral rectus m. Abducens interneurons send excitatory impulses to contralateral oculomotor nucleus A 2nd set of vestibular neurons sends excitatory signals to ipsilateral oculomotornucleus and a 3rd set of vestibular neurons sends inhibitory signals to ipsilateral abducens nucleus

Question 57

Compensatory eye movements present with large head movements characterized by combination of slow phases punctuated by fast return phases

Answer 57

Nystagmus

Question 58

Describe slow and fast phases associated with development of nystagmus

Answer 58

Slow phase: vestibuloocular reflex directs eyes slowly in direction opposite head motion (relies on connections from vestibular nuclei to CN III, IV, and VI nuclei) Fast phase: moving in same direction as that of the head

Question 59

Caloric nystagmus is the movement of endolymph that underlies nystagmus. This can be reproduced with water in the ear. How does response differ with warm vs. cool water?

Answer 59

Warm water — eyes go to ipsilateral side Cool water — eyes go to contralateral side

Question 60

Oculoclonic (oculocephalic) reflex slow phase vs. fast phase

Answer 60

Slow phase: vestibular nuclei —> CN III, IV, and VI nuclei Fast phase: signals that originate from the reticular formation

Question 61

Oculoclonic reflex in intact individual vs. lesioned/comatose patient with depressed RF function but intact brainstem

Answer 61

Intact: both eyes look toward hot/cold fluid Lesioned: deviation of eyes in direction of slow phase of expected nystagmus

Question 62

What are dolls eye movements?

Answer 62

VOR that is normally suppressed when a conscious individual moves head and eyes to one side simultaneously to look at something

Question 63

Brainstem circuitry that controls rapid conjugate eye movements, subdivided into systems controlling horizontal and vertical components of eye movements

Answer 63

Saccades

Question 64

What brain area contains premotor neurons that project to extraocular motor nuclei

Answer 64

Pontine reticular formation/paramedian pontine reticular formation (PPRF)

Question 65

Result of lesions in horizontal gaze center

Answer 65

Horizontal gaze palsies

Question 66

PPRF cells that project to extraocular motor neurons include hwat 2 cell types that produce a burst of APs preceding the activity of motor neurons?

Answer 66

Excitatory burst neurons (EBNs) | Inhibitory burst neurons (IBNs)

Question 67

What brain area carries info about the direction that eyes should move, connecting CN III, IV, and VI to integrate movements directed by gaze centers like PPRF and info about head movement from CN VIII?

Answer 67

Medial longitudinal fasciculus [this is an integral component of saccadic eye movements as well as vestibuloocular and optokinetic reflexes]

Question 68

Alcohol cerebellar degeneration

Answer 68

Chronic alcohol use —> atrophy of cortex of anterior lobe of cerebellum + pontocerebellum and dentate nucleus Late stages: severe LE and trunk ataxia May be seen in conjunction with Korsakoff’s syndrome

Question 69

Autosomal recessive inherited disease causing progressive nervous system damage with the initial symptom of poor coordination, eventually requiring the pt be wheelchair bound

Answer 69

Friedrich’s ataxia [causes functional necrosis and demyelination of proprioceptive neurons in dorsal roots, posterior columns, medial lemniscus, spinocerebellar tracts, and corticospinal tracts as well as damage to purkinje cells, dentate nucleus, and superior cerebellar peduncle]