Cerebellum

Question 1

What are the cerebellar functions?

Answer 1

– Synergy of movement, whereby many elemental muscular contractions are collectively coordinated to create purposeful (perhaps highly complex) movement (e.g., walking).

– Posture, whereby the body is oriented appropriately relative to the vector of gravity.
• Dictated by muscle tone.

Question 2

Describe the cerebellum as a comparator

Answer 2

• The cerebellum receives copies of motor instructions destined for lower motor neurons
• The cerebellum compares sensory feedback to original motor instructions
• Mismatches (errors) are reported back to motor centers

Question 3

What are the basic rules of cerebellar function and dysfunction?

Answer 3

1. Cerebellum regulates ipsilateral body

2. Acute cerebellar damage often yields pronounced
motor deficits (ipsilaterally)

3. Substantial functional recovery may occur in chronic but non-progressive cerebellar damage

Question 4

What does the cerebellar do?

Answer 4

Cerebellar hemisphere indirectly regulates ipsilateral body

Multiple motor homunculi present
– More medial structures regulate trunk
– More lateral structures regulate limb

Question 5

What is the functions of Spino-cerebellum ?

Answer 5

Location: Anterior lobe

Sensory feedback (trunk and limb movement)

Question 6

What are the Cerebro-cerebellum functions?

Answer 6

Primary fissure: posterior lobe

Function: Integrating motor and sensory feedback (precise movements – location and
timing)

Question 7

What is the Vestibulo-cerebellum functions?

Answer 7

Posterolateral fissures: flocculonodular lobe

Afferents from vestibular apparatus (balance, eye
movements)

Question 8

What are the cerebellar peduncles?

Answer 8

The cerebellar peduncles allows for communication between the cerebellum and the brainstem

Question 9

Where do afferent pathways run?

Answer 9

• Afferent fibers arise from the cortex, brainstem and spinal cord
• Examples:

– From the cerebral cortex
• Cerebro-ponto-cerebellarfibers

– From the spinal cord
• Dorsal (posterior) spinocerebellar tract – lower limbs
• Ventral (anterior) spinocerebellar tract – lower limbs
• Cuneocerebellar tract – upper limbs

Question 10

What are the cerebro-ponto-cerebellar inputs?

Answer 10

• Many outputs from precentral gyrus and anterior paracentral lobule of the frontal lobe
• Other frontal areas along with parietal, temporal, and occipital lobes also contributing
• Cortical efferents traveling parallel to corticospinal and corticobulbar fibers terminate in the ipsilateral deep pontine nuclei
• Ponto-cerebellar (transverse) fibers cross the midline to enter the opposite cerebellar hemisphere via the middle cerebellar peduncle

Question 11

What are the spinal inputs of dorsal spinocerebellar?

Answer 11

• Neuromuscular spindles and Golgi tendon organs (trunk and lower limb) communicate with spinal dorsal horn

• The dorsal spinocerebellar pathway ascends ipsilaterally, entering cerebellum via the inferior cerebellar peduncle

Question 12

What are the spinal inputs ventral Spinocerebellar?

Answer 12

• Impulses arise from the Golgi tendon organs of the ipsilateral lower limb
• Synapse at the base of the posterior horn
• Spinal neurons cross cord, ascending to enter via superior cerebellar peduncle.

• Many of these same fibers cross within the cerebellum.
– Pathways crossing twice are functionally identical to undecussated 23 pathways.

Question 13

What are the spinal inputs of Cuneocerebellar?

Answer 13

• Proprioceptors for upper limbs
contribute to the ipsilateral fasciculus cuneatus, which targets medullary nucleus cuneatus

• External arcuate fibers enter inferior cerebellar peduncle as cuneocerebellar pathway

Question 14

Describe the spino-cerebellum (anterior lobe) as a lesion site and its manifestations

Answer 14

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

– Malnutrition (often accompanying chronic alcoholism)

Question 15

Describe the cerebro-cerebellum lesion site and its manifestations

Answer 15

Cerebro-cerebellum (posterior lobe)

– Disturbances affect accuracy and timing of
movement
• Ataxia
• Decomposition of movement
• Dysarthria (slurred monotonous speech)
• Dyssynergia (incoordination of limbs)
– Dysdiadochokinesia (inability to perform rapidly alternating movements)
– Dysmetria (past-pointing)
• Intention tremor
• Hypotonia

Question 16

Describe the vestibulo-cerebellum as a lesion site

Answer 16

Vestibulo-cerebellum (flocculonodular lobe)
– 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

What is the significance of cerebellar tumor?

Answer 17

• The cerebellum is the most common CNS site of neoplastic lesions in the pediatric population
– Low grade gliomas (astrocytoma)
– Embryonal tumors (medulloblastoma)

• Rare in adults
• Presentation: Symptoms of acute intracranial pressure
• Treatment: Surgery, radiation and chemotherapy

Question 18

What are the motor signs of the cerebellar tumor?

Answer 18

– Independent on target affected
• Examples
– Nystagmus
– Truncal ataxia
– Broad-based stance with impaired tandem walking
– Mild hypotonia
– Dysdiadochokinesia

Question 19

What is the significance of cerebellar stroke?

Answer 19

• Cerebellar infarcts are relatively uncommon and represent ≈2% of all ischemic strokes

• Arteries implicated
Posterior inferior cerebellar arteries (PICAs) Anterior inferior cerebellar arteries (AICAs) Superior cerebellar arteries (SCA

Question 20

What are the signs of cerebellar stroke?

Answer 20

Unilateral occlusive disease is common
• Edema within the posterior fossa can cause compression of the 4th ventricle
• Brainstem signs are not uncommon

• Motor signs:
– Dysarthria
– Truncal ataxia

Ipsilateral motor signs
– Dyssynergia
– Intention tremor
– Rebound phenomenon
– Limb ataxia

Question 21

What is alcoholic cerebellar degeneration?

Answer 21

• Vitamin B1 (thiamin) deficiency is linked to degeneration of the rostral vermis and adjacent parts of the remaining anterior cerebellar lobe
• Cortical Purkinje cells often degenerate

• Common causes
– Alcoholics are at higher risk
– Patients who have had bariatric procedures
– Other forms of chronic B1 deficiency

• Motor signs primarily involve legs and trunk
• Some resolution may follow abstinence and dietary supplementation

Question 22

What is Louis-Bar syndrome?

Answer 22

Also known as Ataxia telangiectasia

• Autosomal recessive disorder with multiorgan involvement

• Neurologic: Cerebellar dysfunction
– Widespread degeneration of cerebellar Purkinje
– Delayed development of motor skills
– Most obvious signs relate to walking, talking, facial and ocular movements
– Enlarged cerebellar sulci, cisterns and fourth ventricle seen on MRI/CT

Question 23

What is the impact of Louis-Bar syndrome?

Answer 23

• Skin and eyes tend to express small dilated blood vessels

• On the longer term, heightened sensitivity to ionizing radiation is observed along with increased vulnerability to cancers