CH 16: Cerebellum Flashcards Preview

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Flashcards in CH 16: Cerebellum Deck (47):
1

the cerebellum participates in:

a wide variety of movements

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

2

the cerebellum is essential for:

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

3

voluntary movements can proceed without the cerebellum but would lack:

precision and appear clumsy and disorganized

4

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

specific cognitive functions

5

cerebellar damage has been implicated in:

disturbances of executing functioning

spatial cognition

aspects of personality

linguistic performance

6

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

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

7

what is the tentorium cerebellum?

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

8

what is folia?

numerous parallel folds that corrugate the surface of the cerebellum

9

what is the cerebellar cortex?

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

10

what are the cerebellar nuclei?

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

11

what is the vermis?

cerebral hemispheres?

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

12

what are the 3 transverse cerebellar lobes?

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

13

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

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

14

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

cerebrallar cortex

underlying white matter

deep cerebellar nuclei

15

what are the 3 cell layers of the cerebellar cortex?

1- molecular layer (outermost)

2- pukinje cell layer (middle)

3- granular layer (innermost)

16

describe the molecular layer of the cerebellar cortex

the outermost layer

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

17

describe the Purkinje cell layer of the cerebellar cortex

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

18

describe the granular layer of the cerebellar cortex

the innermost lawyer

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

glial cell processes encase each glomerulus

19

what is the synaptic organization of the cerebellar cortex?

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

20

the afferents to the cortex terminate :

in the granule cell layer as mossy fibers

OR

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

21

what are mossy fiber afferents?

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

22

what are climbing fiber afferents?

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)

23

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

granule cells

24

mossy fiber inputs excites Purkinje cells indirectly and evokes:

simple spikes

a single AP

25

climbing fiber input excites Purkinje fibers directly and evokes:

complex spikes

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

26

aminergic afferent projections reach:

all 3 cortex layers and are thought to be inhibitory

27

summary of information processing:

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

28

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

afferent fibers

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

29

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

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

30

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

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

31

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

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

32

where do afferents to the cerebellar cortex come from?

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

33

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

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

34

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

receive afferent input from the SC

function primarily in the control of posture and locomotion

35

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

vestibular system

vestibular function: balance, posture, and eye movements

36

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

cerebral cortex

focus on the control of finely coordinated movements of the extremities

concerned with executive functioning, visual-spatial processing and language production

37

what efferent fibers distribute from the fastigial nucleus?

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

38

what efferent fibers distribute from the interposed nuclei?

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

39

what efferent fibers distribute from the dentate and interposed nuclei?

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

40

the intent to perform a movement originates in the :

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

41

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

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

42

what constitutes the midline zone?

what are the 5 clinical signs of midline zone dysfunction?

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

43

what constitutes the lateral zone?

what are the 14 clinical signs of lateral zone dysfunction?

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

44

what is spinocerebellar ataxias?

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

45

what is Friedreich's ataxia?

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

46

what is sporadic olivopontocerebellar atrophy?

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

47

what is alcoholic cerebellar degeneration?

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