Cerebellum

Question 1

describe cerebellar function and dysfunction

Answer 1

• cerebellum regulates ipsilateral body
• acute cerebellar damage often yields pronounced motor deficits (ipsilaterally)
• substantial functional recovery may occur in chronic but non-progressive cerebellar damage

Question 2

describe the method of indirect motor control by the cerebellum

Answer 2

• motor centers (primary motor cortex) transmit signals directly or indirectly to LMNs to produce purposeful movement or simply to influence muscle tone or reflexive responsiveness
• the cerebellum compares sensory feedback with original motor instructions
• with mismatched motor instructions and outcomes, the cerebellum sends corrective signals to motor centers, thereby refining subsequent motor instructions

Question 3

describe the cerebellar homunculi

Answer 3

Question 4

describe the 3 functionally distinct zones of the cerebellum

Answer 4

• vestibuli-cerebellum
  
  • flocculonodular lobe
  • afferents from vestibular apparatus (balance, eye movements)
• spino-cerebellum
  
  • anterior lobe
  • sensory feedback (trunk and limb movement)
• cerebro-cerebellum
  
  • posterior lobe
  • integrating motor with sensory feedback (precise movements - location and timing)

Question 5

describe the function of the middle, superior and inferior cerebellar peduncles

Answer 5

• superior cerebellar peduncles largely efferent
• middle and inferior cerebellar peduncles large afferent, with the inf. cerebellar peduncle also carrying many efferents

Question 6

Answer 6

Question 7

describe supraspinal cerebellar input

Answer 7

• the precentral gyrus and ant. paracentral lobule of the frontal lobe emit large volumes of motor info. via the corticospinal and corticobulbar motor systems
• other frontal areas along with parietal, temporal and occipital lobes also contribute
• copies of corticospinal and corticobulbar signals destined for LMNs also terminate in the ipsilateral deep pontine nuclei
• 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

Question 8

describe dorsal spinocerebellar inputs

Answer 8

• 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 inf. cerebellar peduncle

Question 9

describe the ventral spinocerebellar system

Answer 9

• an array of receptors contribute 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)
• 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)

Question 10

describe the cuneocerebellar system

Answer 10

• proprioceptors for the upper limbs contribute to the ipsilateral fasciculus cuneatus, which terminates in the medullary accessory nucleus cuneatus
• external arcuate fibers enter the cerebellum through the ipsilateral inf. cerebellar peduncle as the cuneocerebellar pathway

Question 11

describe the cortical organization and cerebellar output

Answer 11

• cortical granule cells (granular layer) receive inputs from mossy fibers
• granule cells receive inputs from mossy fibers then ascend to superficial (molecular) cortical layer (molecular layer) therein bifurcating mediolaterally
• Golgi cells provide feedback inhibition of granule cells
• dendrites of Purkinje cells occupy the superficial (molecular layer)
• parallel fibers (axons of granule cells) excite Purkinje cells and local inhibitory interneurons

Question 12

describe the 3 deep cerebellar nuclei

Answer 12

• the vermis and flocculonodular lobe communicate with the medially located fastigial nucleus
• the paravermis communicates with the interposed nucleus
• the lateral hemispheres communicate with the largest and lateral-most deep cerebellar masses of gray matter, the dentate nucleus

Question 13

Answer 13

Question 14

describe the deep nuclear outputs to extracerebellar motor centers

Answer 14

• fastigial efferents reach:
  
  • medial vestibular nuclei (bilaterally) to influence reflexive movements of the eyes, head and neck
  • lateral vestibular nucleus ipsilaterally to influence movement of the limbs and the trunk
  • pontine and medullary reticular formations to influence a broad array of muscles
• efferents of the interposed nucleus communicate with the contralateral red nucleus to influence the rubrospinal system
• dentate nucleus receives input from the lateral cerebellar hemispheres and communicates with the contralateral ventrolateral nucleus of the thalamus to influence cortical motor systems

Question 16

describe a lesion of the vestibulo-cerebellum (flocculonodular lobe)

Answer 16

• disturbances affect equilibrium-related motor functions
  
  • nystagmus (ocular ataxia)
  • tilted head
  • titubation (head-nodding)
  • truncal ataxia (imbalance) with compensatory wide-based stance
    
    • impaired tandem walking

Question 17

describe a lesion in the spino-cerebellum (anterior lobe)

Answer 17

• disturbances affect posture and movement of limbs
  
  • ataxias of the limbs common (ipsilateral)
• gait ataxia accompanied by lurching to the side of the lesion

Question 18

describe a lesion in the cerebro-cerebellum (posterior lobe)

Answer 18

• disturbances affect accuracy and timing of movement
  
  • ataxia
  • decomposition of movement
  • dysaryhria (slurred monotonous speech)
  • dyssynergia (uncoordination of limbs)
    
    • dysdiadokinesia
    • dysmetria
  • intention tremor
  • hypotonia
  • rebound phenomenon

Question 19

describe a cerebellar tumor

Answer 19

midline astrocytomas occur most commonly in children

• motor signs:
  
  • nystagmus
  • truncal ataxia
  • broad-based stance with impaired tandem walking
  • hypotonia
• other manifestations:
  
  • headache
  • hydrocephalus
  • intracranial pressure elevated (yielding papilledema)
  • nausea and vomiting

Question 20

describe a cerebellar stroke

Answer 20

• vertebral arterial system is implicated
  
  • unilateral occlusive disease is common
• motor signs:
  
  • dysarthria
  • dyssynergia (ipsilateral)
    
    • dysmetria = difficulting measuring
    • dysdiadokinesia = dif. performing repetitive acts
  • intention tremor (ipsilateral)
  • rebound phenomenon (ipsilateral)
  • limb ataxia (ipsilateral)
  • truncal ataxia
• brainstem signs are not uncommon
  
  • cerebellar arteries supply the brainstem en route to the cerebellum

Question 21

describe how malnutrition affects the cerebellum

Answer 21

• vitamin B1 (thiamine) deficiency linked to degeneration of the rostral vermis and adjacent parts of the remaining ant. cerebellar lobe
  
  • alcoholics are at higher risk
• cortical Purkinje cells often degenerate
• motor signs primarily involve legs and trunk
• some resolution may follow abstinence and dietary supplementation

Question 22

describe Louis-Bar syndrome

Answer 22

• autosomal recessive disorder with widespread degeneration of cerebellar Purkinje cells and compromised immune function (chr. 11)
• delayed development of motor skills accompanies increased vulnerability to infxn
• most obvious signs relate to walking, talking, facial and ocular movements
• on the longer term, heightened sensitivity to ionizing radiation is observed along with increased vulnerability to cancers
• skin and eyes tend to express small dilated blood vessels

Question 23

describe cerebellar cognitive affective syndrome (CCAS)

Answer 23

• lesions of the posterior lobe are considered to correlate with dysfunctional cognitive and emotional systems, leading to:
  
  • emotional blunting and depression, disinhibition and psychosis
  • executive, visual-spatial and linguistic deterioration
  • the condition is conceptualized in relation to “dysmetria of thought”