CH 16: Cerebellum Flashcards
the cerebellum participates in:
a wide variety of movements
it maintains the fine control and coordination of both simple and complex movements
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
voluntary movements can proceed without the cerebellum but would lack:
precision and appear clumsy and disorganized
the cerebellum not only participates in motor processes but also in certain:
specific cognitive functions
cerebellar damage has been implicated in:
disturbances of executing functioning
spatial cognition
aspects of personality
linguistic performance
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
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
what is folia?
numerous parallel folds that corrugate the surface of the cerebellum
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
what are the cerebellar nuclei?
4 pairs of deep cerebellar nuclei: from medial to lateral: fastigial globose emboliform dentate
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
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
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
the cerebellum can be subdivided into 3 longitudinal strips arranged mediolaterally that include:
cerebrallar cortex
underlying white matter
deep cerebellar nuclei
what are the 3 cell layers of the cerebellar cortex?
1- molecular layer (outermost)
2- pukinje cell layer (middle)
3- granular layer (innermost)
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
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
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
what is the synaptic organization of the cerebellar cortex?
the cerebellar cortex contains 2 types of inhibitory interneurons and 1 type of excitatory interneuron
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
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
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)
what is the only cell that causes excitation within the cerebellar cortex?
granule cells
mossy fiber inputs excites Purkinje cells indirectly and evokes:
simple spikes
a single AP
climbing fiber input excites Purkinje fibers directly and evokes:
complex spikes
an AP followed by a long lasting depolarization with multiple small wavelets
aminergic afferent projections reach:
all 3 cortex layers and are thought to be inhibitory
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
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
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
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
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
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
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
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
the flocculonodular lobe receives afferent input from the?
what is its primary function?
vestibular system
vestibular function: balance, posture, and eye movements
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
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
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
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
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
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
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
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
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
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
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
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
