CH 16: Cerebellum

Question 1

the cerebellum participates in:

Answer 1

a wide variety of movements

it maintains the fine control and coordination of both simple and complex movements

Question 2

the cerebellum is essential for:

Answer 2

coordinating posture & balance in walking/running

executing sequential movements in eating, dressing, writing

producing rapidly alternating repetitive movements and smooth pursuit movements: including trajectory, velocity and acceleration

Question 3

voluntary movements can proceed without the cerebellum but would lack:

Answer 3

precision and appear clumsy and disorganized

Question 4

the cerebellum not only participates in motor processes but also in certain:

Answer 4

specific cognitive functions

Question 5

cerebellar damage has been implicated in:

Answer 5

disturbances of executing functioning

spatial cognition

aspects of personality

linguistic performance

Question 6

what is the basic anatomy of the cerebellum?
where is it in the skull?
how does it attach to other structures?

Answer 6

the cerebellum consists of a bilaterally symmetrical structure that is situated in the posterior cranial fossa attaches to the medulla, pons and midbrain by 3 pairs of cerebellar peduncles

these peduncles lie at the sides of the 4th ventricle on the ventral aspect of the cerebellum

Question 7

what is the tentorium cerebellum?

Answer 7

a transverse fold of the dura mater, stretches horizontally over the superior surface of the cerebellum and separates it from the overlying occipital lobes of the cerebrum

Question 8

what is folia?

Answer 8

numerous parallel folds that corrugate the surface of the cerebellum

Question 9

what is the cerebellar cortex?

Answer 9

a layer of gray matter that covers the surface of the cerebellum and encloses an internal core of white matter

Question 10

what are the cerebellar nuclei?

Answer 10

4 pairs of deep cerebellar nuclei:
from medial to lateral:
fastigial
globose
emboliform
dentate

Question 11

what is the vermis?

cerebral hemispheres?

Answer 11

the cerebellum includes:

a midline structure in the cerebellum =vermis

2 large lateral masses= cerebral hemispheres

together these can be divided transversely into 3 lobes

Question 12

what are the 3 transverse cerebellar lobes?

Answer 12

1- flocculonodular lobe
-paired flocculi
-nodulus
-separated from the posterior lobe by the posterolateral fissure
“archicerebellum”
-receives input from the vestibular nuclei

2- anterior lobe
-lies posterior to the primary fissure
“paleocerebellum”
-receives input form the spinocerebellar and trigeminocerebellar pathways

3- posterior lobe
-contains the major portions of the cerebellar hemispheres
“neocerebellum”
-contains the cerebellar tonsils - lie immediately above the foramen magnum
-receives projections from the cerebral hemispheres

Question 13

what a disease process (tumor or hemorrhage) in the cerebellum increases pressure in the posterior fossa, the cerebellar tonsils can..?

Answer 13

herniate downward into the foramen magnum and can compress the medulla

this threatens survival because compression of the medulla leads to dysfunction of RF neurons in the BS that control BP and respiration

Question 14

the cerebellum can be subdivided into 3 longitudinal strips arranged mediolaterally that include:

Answer 14

cerebrallar cortex

underlying white matter

deep cerebellar nuclei

Question 15

what are the 3 cell layers of the cerebellar cortex?

Answer 15

1- molecular layer (outermost)

2- pukinje cell layer (middle)

3- granular layer (innermost)

Question 16

describe the molecular layer of the cerebellar cortex

Answer 16

the outermost layer

Contains:

• 2 types of neurons (stellate cells, basket cells)
• dendrites of Purkinje and Golgi type II cells
• axons of granule cells

Question 17

describe the Purkinje cell layer of the cerebellar cortex

Answer 17

middle layer

contains the cell bodies of Purkinje cells

• these large, flasklike neurons have enormous dendritic arborizations extending upward into the molecular layer
• run perpendicular to the million parallel fibers in the molecular layer
• long axons synapse either on deep cerebellar nuclei or vestibular nuclei

Question 18

describe the granular layer of the cerebellar cortex

Answer 18

the innermost lawyer

contains massive numbers of granule cells (neurons), Golgi type II cells and glomeruli

glial cell processes encase each glomerulus

Question 19

what is the synaptic organization of the cerebellar cortex?

Answer 19

the cerebellar cortex contains 2 types of inhibitory interneurons and 1 type of excitatory interneuron

Question 20

the afferents to the cortex terminate :

Answer 20

in the granule cell layer as mossy fibers

OR

in the molecular layer on the dendrites of Purkinje cells as climbing fibers

Question 21

what are mossy fiber afferents?

Answer 21

enter the cerebellum from the SC, pontine nuclei, vestibular ganglia and nuclei, trigeminal nuclei, and RF nuclei

mossy fibers use glutamate as a neurotransmitter

mossy fibers synapse on granule cells (in granular layer) and use glutamate as a neurotransmitter at their parallel fiber synapses with Purkinje cells and with interneurons: basket cells, stellate cells, and golgi cells.

these interneurons, in turn, release GABA and evoke inhibitory effects

Question 22

what are climbing fiber afferents?

Answer 22

originate exclusively in the inferior olive

release glutamate or aspartate to excite the Purkinje cell dendrites on which they synapse

Purkinje cells release GABA and thereby inhibit the deep cerebellar nuclei

these nuclei provide the origin of the efferent fibers from the cerebellum to the inferior oleic, RF, vestibular nuclei, red nucleus and thalamus

all these projections release glutamate (except those in the inferior olive which release GABA)

Question 23

what is the only cell that causes excitation within the cerebellar cortex?

Answer 23

granule cells

Question 24

mossy fiber inputs excites Purkinje cells indirectly and evokes:

Answer 24

simple spikes

a single AP

Question 25

climbing fiber input excites Purkinje fibers directly and evokes:

Answer 25

complex spikes an AP followed by a long lasting depolarization with multiple small wavelets

Question 26

aminergic afferent projections reach:

Answer 26

all 3 cortex layers and are thought to be inhibitory

Question 27

summary of information processing:

Answer 27

afferent input from essentially all sources reaches both the deep cerebellar nuclei and the cerebral cortex and leads to an increase in excitability of the deep nuclei and the purkinje cells of the cerebellar cortex the purkinje cells provide strong inhibitory control over neurons of the deep nuclei the inhibitory control of Purkinje cells over the excitability of the deep cerebellar nuclei is a key aspect of cerebellar function through info received from afferents and interactions between the cerebellar cortex and the deep nuclei, the cerebellum monitors ongoing movements and triggers new or modified movements. the cerebellum can ensure that the speed and accuracy of movements are adequate for each task the motor system undertakes

Question 28

what fibers does the inferior cerebellar penduncle /restiform body primarily consist of?

Answer 28

afferent fibers single efferent pathway- fastigiobulbar tract/juxtarestiform body which projects to the vestibular nuclei and completes a vestibular circuit through the cerebellum

Question 29

what are the 6 sources that contribute to the inferior cerebellar peduncle?

Answer 29

1- vestibular nerve/nuclei 2- inferior olicary nuclei 3-dorsal spinocerebellar tract 4- some of the rostral spinocerebellar tract 5- cuneocerebellar tract from the ACN in medulla 6-reticulocerebellar fibers

Question 30

what does the middle cerebellar peduncle (brachium pontis) consist of?

Answer 30

almost entirely of crossed afferent fibers from the contralateral pontine nuclei in the gray substance of the basal pons

Question 31

what does the superior cerebellar peduncle (brachium conjunctivum) consist of?

Answer 31

principally of efferent projections from the cerebellum- rural, thalamic and reticular projections arise from the dentate and interposed nuclei also contains afferent projections from the ventral spinocerebellar tract and a portion of the rostral spinocerebellar tract and trigeminocerebellar projections

Question 32

where do afferents to the cerebellar cortex come from?

Answer 32

from the cerebral cortex from skin, joints, muscles of the limbs and trunk that is mediated by the 3 spinocerebellar tracts (dorsal, ventral and rostral) and the cuneocerebellar tract auditory, vestibular and visual senses direct connections from neurons in the hypothalamus

Question 33

how does afferent information get from the cerebral cortex to the cerebellar cortex?

Answer 33

neuronal activity emanating from the cerebral cortex reaches the cerebellar cortex through 3 cerebrocerebellar projection pathways CORTICOPONTINECEREBELLAR PATHWAY (largest) consists of a crossed path connecting most of the cortex of one cerebral hemisphere with the cerebellar hemisphere of the opposite side by way of the CORTICOPONTINE tract and the PONTOCEREBELLAR projections the corticopontine projections contain information from primary motor and sensory areas of the cerebral cortex and also from associative areas (prefrontal and parietal regions) and from the primary visual cortex, and someone the auditory cortex these pontocerebellar fibers ascend through the middle cerebellar peduncle motor areas of the cerebral cortex include the cerebra-olivocerebellar and cerebroreticulo-cerebelar pathways

Question 34

the vermis and anterior lobe and the caudal part of the posterior lobe receive afferent input from ? what is its primary function?

Answer 34

receive afferent input from the SC function primarily in the control of posture and locomotion

Question 35

the flocculonodular lobe receives afferent input from the? | what is its primary function?

Answer 35

vestibular system vestibular function: balance, posture, and eye movements

Question 36

the cerebellar hemispheres receive their major input from the? what is its primary function?

Answer 36

cerebral cortex focus on the control of finely coordinated movements of the extremities concerned with executive functioning, visual-spatial processing and language production

Question 37

what efferent fibers distribute from the fastigial nucleus?

Answer 37

sends efferents fibers to the reticular and vestibular nuclei of the BS these nuclei project into the SC where they participate in the control of posture and balance projections from these nuclei into the upper BS assist in the regulation of conjugate eye movements

Question 38

what efferent fibers distribute from the interposed nuclei?

Answer 38

send projections through the superior cerebellar peduncle to the magnocellular division of the red nucleus on the contralateral side. gives rise to axons of the rubrospinal tract which crosses the midline and descends into the SC hence this pathway originates and terminates on the same side the rubrospinal tract contributes to locomotion and coordinated movements of the extremities

Question 39

what efferent fibers distribute from the dentate and interposed nuclei?

Answer 39

project through the superior cerebellar peduncle to the contrlateral red nucleus and the ventral lateral and intralaminar nuclei of the thalamus fibers from the dentate give rise to the rubro-olivary tract- descend ipsilaterally through the BS in the central segmental tract to terminate in the inferior olivary complex and thereby provide a feedback loop to the dentate nucleus and lateral zone of the cerebellar cortex

Question 40

the intent to perform a movement originates in the :

Answer 40

motor association areas of the cerebral cortex, including the supplementary motor cortex these areas act in cooperation with the lateral portions of the cerebellar hemispheres and dentate nuclei during the early phases of movement planning the result is a command to move, which involves the dentate nuclei

Question 41

the intermediate parts of the cerebellar hemispheres, including the interpositus nuclei, receive :

Answer 41

information about the progress of the ongoing movement by inputs from collaterals of pyramidal tract fibers mediated by way of the pontine nuclei and also from peripheral receptors in the body parts being moved

Question 42

what constitutes the midline zone? what are the 5 clinical signs of midline zone dysfunction?

Answer 42

anterior and posterior parts of the vermis, the flocculonodular lobe and the fastigial nuclei 1- disorders of stance and gait-- wide base, can't walk in tandem, NO ataxia 2-titubation- rhythmic tremor 3- rotated or tilted postures of the head 4-ocular motor disorders- spontaneous nystagmus 5- affective disturbances- flattening or blunting of emotional expression

Question 43

what constitutes the lateral zone? what are the 14 clinical signs of lateral zone dysfunction?

Answer 43

cerebellar hemisphere and the dentate and interposed nuclei 1- decomposition of movement- jerky, irregular 2- disturbances of stance and gait- wide base, tendency to fall side, fwd, backward 3- hypotonia 4- dysarthria- speech 5- dysmetria- disturbance of trajectory/placement 6- dysdiadochokinesis and dysrhythmokinesis 7- ataxia- errors in sequence/ speed, veers side to side 8- tremor 9- impaired check and rebound 10- ocular motor disorders- nystagmus 11-disturbances of executive functioning- deficient planning 12- impaired spatial cognition 13- personality change- flattening or blunting 14- linguistic difficulties

Question 44

what is spinocerebellar ataxias?

Answer 44

inherited disorder causes degeneration of the inferior olives, pons, cerebellum, and various other components of the NS presents with ataxia, dysarthria, and incoordination of limb movements

Question 45

what is Friedreich's ataxia?

Answer 45

inherited spinocerebellar ataxia begins in childhood/teen begins with ataxia develops scoliosis, pes cavus, limb weakness and ataxia progresses to include paraparesis (severe leg weakness) with loss of the muscle stretch reflexes and position and vibration sense in the limbs

Question 46

what is sporadic olivopontocerebellar atrophy?

Answer 46

progressive neurodegenerative disease of unknown case gradual loss of neurons of the inferior olives, pons, and cerebellar cortex and causes ataxia of gait, dysarthria, cerebellar tremors of the trunk and limbs and incoordination of movements of all limbs some evolve into multiple system atrophy, which includes cerebellar ataxia and autonomic insufficiency and parkinsonian features

Question 47

what is alcoholic cerebellar degeneration?

Answer 47

severe chronic alcoholism with malnutrition degenerative changes appearing in the anterior and superior parts of the cerebellar vermis are associated with ataxia of gait but with preservation of speech and coordinated movements of the UEs