Module E-08 Flashcards
What Aspects of Motor Function are under (Indirect) Cerebellar Regulation?
1) Synergy of movement: Collective coordination of elemental muscular contractions to create purposeful (perhaps highly complex) motoric output (e.g., walking).
2) Posture: Orientation of body parts relative to each other and the vector of gravity.
3) Muscular tone: Basal levels of contraction of muscles.
Describe the method of the indirect control that is being done by the cerebellum
- The cerebellum acts as a comparator
o Motor centers (e.g., primary motor cortex) transmit signals directly or indirectly to lower motor neurons to produce purposeful movement or simply to influence muscle tone or reflexive responsiveness
o Copies of such motor instructions reach the cerebellum
o The cerebellum compares sensory feedback with original motor instructions
o With mismatched motor instructions and outcomes, the cerebellum sends corrective signals to motor centers,
thereby influencing subsequent motor instructions
o Under the feedback-driven guidance of the cerebellum, the motor centers continually adjust output to facilitate
smoothly coordinated and posturally appropriate movements (this necessarily implies spatial and
temporal accuracy of movement)
Which side of the body does the cerebellum control?
Cerebellum indirectly regulates ipsilateral body
What occurs in acute cerebellar damage?
often yields pronounced motor deficits (ipsilaterally)
In what type of Cerebellar damage recovery possible?
Substantial functional recovery often occurs with long-standing but nonprogressive cerebellar damage
Describe embryological development of Cerebellum
emerged embryologically as a protuberance of the
metencephalon to occupy much of the posterior cranial fossa
Describe the General structure of the cerebellum
o The cerebellum is grossly hemispheric
o Hemispheres are separated by a midline vermis (worm)
A sagittal view of the vermis reveals an ornate complex of white matter (arbor vitae or tree of life) that penetrates
superficial gray matter
Name the Cerebellar lobes and their location
1) Anterior lobe: Superior to the primary fissure
2) Posterior lobe: Inferior to the primary fissure
3) Flocculonodular lobe: Mediolaterally oriented strip of tissue situated ventrally on the cerebellum, separated from the posterior lobe by the posterolateral fissure
Describe the somatotopic map of the cerebellum
o The trunk is functionally regulated by more medial cerebellar structures
o Limbs are functionally regulated by more laterally
What are the 3 functional zones of the cerebellum and describe their locations?
- Vestibulo-cerebellum- flocculonodular lobe
- Spino-cerebellum - anterior lobe
- Cerebro-cerebellum - posterior lobe
Function of the Vestibulo-cerebellum
afferents from vestibular apparatus to permit regulation of balance andeye movements
Function of the Spino-cerebellum
The spinal cord provides this region with sensory feedback regarding consequences of motor activity, thereby assisting with regulation of gross truncal and limb movements
Function of the Cerebro-cerebellum
Integrating motor with sensory feedback coordinates and
smoothes movements requiring precision of location and
timing
What forms the cerebellar peduncles?
Cerebellar efferents and afferents
Where are the fibers going from each of the cerebellar peduncles?
o Middle cerebellar peduncles largely carry information from the pons into the cerebellum
o Superior and inferior cerebellar peduncles carry bidirectional traffic, with the inferior cerebellar peduncle being the greater conductor of cerebellar afferents
o Superior cerebellar peduncles transmit cerebellar signals to the pons and midbrain (except those destined for the vestibular nuclei)
o Inferior cerebellar peduncles relay much information from
spinal levels into the cerebellum, although the superior cerebellar peduncle also contributes
o Communications with the olive, cranial nerve VIII and the vestibular nuclei also involve the inferior cerebellar peduncles
How does afferents allow cerebellum to act as a comparator?
- Motor systems (e.g., corticospinal system) advise the cerebellum of their impending influence on lower motor neurons
- Somatosensory systems (e.g., dorsal spinocerebellar system) advise the cerebellum of the results of motor system output
- Comparison of intended outcomes (motor instructions) with actual outcomes (somatosensory feedback) permit the cerebellum to transmit corrective instructions to motor systems
Describe the Cerebro-ponto-cerebellar Inputs (Copy of Motor Instructions)
o The precentral gyrus and anterior paracentral lobule of the frontal lobe emit large volumes of motor information, as part of the corticospinal and corticobulbar motor systems
o Other frontal areas along with parietal, temporal, and occipital lobes also contribute
o Copies of corticospinal and corticobulbar signals destined for lower motor neurons also terminate in the ipsilateral deep pontine nuclei
o Ponto-cerebellar (transverse) fibers then cross the midline to enter the cerebellar hemisphere opposite to the cortical site of origin via the middle cerebellar peduncle
Name 3 Examples of Spinal cerebellar Input (Sensory Feedback)
1) Dorsal spinocerebellar system
2) Ventral spinocerebellar system
3) Cuneocerebellar system
Describe the Dorsal spinocerebellar system input to the cerebellum
- Neuromuscular spindles and Golgi tendon organs transmit signals related to specific muscles (of the lower
body) into the spinal dorsal horn - The dorsal spinocerebellar pathway ascends ipsilaterally to enter the cerebellum via the inferior cerebellar peduncle
Describe the Ventral spinocerebellar system input to the cerebellum
- An array of receptors contributes to analysis of whole-limb movement, communicating with the spinal gray matter
- Spinal neurons send axons across the cord to ascend to the superior cerebellar peduncle, thereby entering the cerebellum
- Many of these same fibers cross a second time (within the
cerebellum) - Note that this pathway, which crosses the nervous system twice, is functionally similar to a pathway that does not
cross (i.e., one side of the cerebellum indirectly regulates the ipsilateral body)
Describe the Cuneocerebellar system input to the cerebellum
- Proprioceptors for the upper limbs contribute to the ipsilateral fasciculus cuneatus, which terminates in the
medullary nucleus cuneatus - External arcuate fibers enter the cerebellum through the ipsilateral inferior cerebellar peduncle as the cuneocerebellar pathway
Describe the histology of the cerebellum
- Beneath the meninges is the cerebellar cortex (analogous to cerebral cortex)
- Beneath the cerebellar cortex is subcortical white matter (analogous to cerebral white matter)
- Embedded within the subcortical white matter are deep cerebellar nuclei (analogous to the basal nuclei [ganglia] of the cerebrum)
Near the deep cerebellar nuclei is the ventricular system,
specifically the fourth ventricle (analogous to the lateral cerebral ventricles)
What are the 2 types of fibers that enter the cerebellum?
o Climbing fibers arise from the inferior olivary nuclei
o Mossy fibers constitute the remainder of cerebellar afferents
Describe the cerebellar cortical organization
The cerebellar cortex is organized as folia (little folds) and is laminated
o Closest to the white matter lie cortical granule cells,
o Between the molecular and granule layers is the Purkinje layer, occupied by the large Purkinje somata
o Outermost layer is Molecular layer
Describe fibers of the Granular layer
Granule cell axons ascend to the superficial cortical layer
(molecular layer), therein bifurcating, with one process traveling medially and the other traveling laterally
Golgi cells provide inhibitory feedback to granule cells
Dendrites of Purkinje cells occupy the superficial (molecular) layer of cortex
Parallel fibers (axons of granule cells) excite the dendrites of Purkinje cells and local inhibitory interneurons
Climbing fibers ascend to synapse directly on the dendrites of Purkinje cells, spreading excitation in the rostro-caudal plane
Describe fibers of the Purkinje layer
Once excited, the Purkinje cells transmit signals down their axons, which exit the cortical gray matter
Purkinje cells commonly release GABA onto deep
cerebellar nuclear cells
Deep nuclear cells emit cerebellar efferent axons
What are the 3 deep cerebellar nuclei?
1) The vermis and flocculonodular lobe communicate with the medially located FASTIGIAL NUCLEUS
2) The paravermis communicates with the INTERPOSED NUCLEUS
3) The lateral hemispheres communicate with the largest and lateralmost deep cerebellar masses of gray matter, the DENTATE NUCLEUS (which looks like a tooth-mark)
Function of Efferents from Fastigial Nucleus
o Medial vestibular nuclei (bilaterally) to influence reflexive movements of the eyes, head and neck
o Lateral vestibular nucleus ipsilaterally to influence movement of the limbs and the trunk
o Pontine and medullary reticular formations to influence a broad array of muscles
Function of Efferents of the interposed nucleus
communicate with the contralateral red nucleus to influence the rubrospinal system
Function of Efferents of the Dentate nucleus
receives input from the lateral cerebellar hemispheres
and communicates with the contralateral ventrolateral nucleus of the thalamus to influence cortical motor systems
Effect of lesion in Vestibulo-cerebellum
- Disturbances affect equilibrium-related motor functions
o Nystagmus (ocular ataxia)
o Tilted head
o Titubation (head-nodding)
o Truncal ataxia (imbalance) with compensatory wide-based stance- Impaired tandem walking
Effect of lesion in Spino-cerebellum (Anterior Lobe)
– Disturbances affect posture and movement of limbs
• Ataxias of the limbs common (ipsilateral)
– Gait ataxia accompanied by lurching to the side of the lesion
Effect of lesion in Cerebro-cerebellum (Posterior Lobe)
– Disturbances affect accuracy and timing of movement
• Ataxia
• Decomposition of movement
• Dysarthria (slurred monotonous speech)
• Dyssynergia (uncoordination of limbs)
*Dysdiadokinesia (inability to perform rapidly alternating
movements)
* Dysmetria (past-pointing)
• Intention tremor
• Hypotonia
• Rebound phenomenon
5 causes of Cerebellar lesions
1) Tumor
2) Cerebellar Stroke
3) Malnutrition
4) Louis-Bar Syndrome
5) Cerebellar Cognitive Affective Syndrome (CCAS)
Type of Cerebellar tumor
Midline astrocytomas occur most commonly in children
Symptoms in Cerebellar tumors
- Motor signs: o Broad-based stance with impaired tandem walking o Nystagmus o Truncal ataxia - Other manifestations: o Headache o Hydrocephalus o Intracranial pressure elevated (often yielding papilledema) o Nausea and vomiting
What is cause of cerebellar stroke?
- Vertebral arterial system is implicated - Unilateral occlusive disease is common
Symptoms of Cerebellar stroke
- Motor signs: o Dysarthria o Dyssynergia (ipsilateral) - Dysmetria - Dysdiadokinesia o Intention tremor (ipsilateral) o Limb ataxia (ipsilateral) o Rebound phenomenon (ipsilateral) o Truncal ataxia - Brainstem signs are not uncommon o Cerebellar arteries supply the brainstem en route to the cerebellum
How does Malnutrition cause lesion of the cerebellum?
- Vitamin B1 deficiency linked to degeneration of the anterior vermis and adjacent parts of the remaining anterior cerebellar lobe
- Cortical Purkinje cells often degenerate, heralding reactive gliosis
Who is most at risk in malnutrition caused cerebellar lesions?
Alcoholics are at risk
What are cerebellar symptoms seen in malnutrition ?
- Cortical Purkinje cells often degenerate, heralding reactive gliosis
- Motor signs (primarily of the legs and trunk):
o dysmetria of legs (heel-shin test) and lurching gait
o truncal ataxia and intention tremor
Can cerebellar defects be reversed if caused by malnutrition?
Some recovery may follow abstinence from alcohol and dietary supplements
What is Louis-Bar Syndrome?
Autosomal recessive disorder with widespread degeneration of cerebellar Purkinje cells and compromised immune function (chromosome 11)
What are manifestations of Louis-Bar Syndrome?
- Delayed development of motor skills accompanies increased vulnerability to infection
- Most obvious signs relate to walking, talking, facial and ocular movements
- On the longer term, sensitivity to ionizing radiation is observed along with increased vulnerability to cancers
- Skin and eyes tend to express small dilated blood vessels
What is CCAS?
Lesion of Posterior lobe
Symptoms of CCAS
- correlate with failures of cognitive and emotional systems, leading to:
o Emotional blunting and depression, disinhibition and psychosis
o Executive, visual-spatial, and linguistic deterioration - “dysmetria of thought”
