Functional Divisions of the Cerebellum [2+3+3+4]

1. Functional Divisions [2 marks]

2. Connections (Afferent and Efferent) [3 marks]

Afferent (Input) Pathways

• Vestibulocerebellum: Receives input from vestibular nuclei (via inferior peduncle)
• Spinocerebellum: Receives input from spinal cord (spinocerebellar tracts)
• Cerebrocerebellum: Receives input from cerebral cortex via corticopontine fibers (via middle peduncle)

Efferent (Output) Pathways

3. Functions of the Cerebellum [3 marks]

1. Coordination of voluntary movements - smoothing and fine-tuning of motor activity; prevents errors in range, force, and direction of movement
2. Maintenance of equilibrium and posture - via vestibulocerebellum; regulates muscle tone against gravity
3. Motor planning and procedural memory - lateral hemispheres involved in planning motor programs for extremities and learning motor sequences
4. Regulation of muscle tone - via connections to gamma motor neurons; lesions cause hypotonia
5. Coordination of eye movements - flocculonodular lobe controls vestibulo-ocular reflex and smooth pursuit
6. Synergy of muscle groups - ensures appropriate co-contraction and sequencing of agonist/antagonist muscle groups
7. Non-motor functions - some evidence for roles in cognitive processing and language via dentate-thalamo-cortical connections

4. Clinical Manifestations Following Cerebellar Lesion [4 marks]

A. Dysmetria

• Inability to accurately gauge distance/direction of movement
• Demonstrated by finger-nose test (past-pointing) and heel-knee-shin test
• Overshoot = hypermetria; undershoot = hypometria

B. Ataxia

• Gait ataxia: Wide-based, reeling, drunken gait; patient tends to fall toward the side of the lesion
• Truncal ataxia: With vermis lesions - inability to sit or stand steadily (titubation - tremor of the trunk/head)
• Appendicular ataxia: Incoordination of limb movements (lateral hemisphere lesions)

C. Nystagmus

• Gaze-evoked nystagmus is most common; may be multidirectional (unlike peripheral vestibular nystagmus)
• Ocular dysmetria - saccades overshoot/undershoot targets
• Flocculonodular lesions cause jerky saccadic intrusions during smooth pursuit

D. Intention Tremor (Action Tremor)

• Tremor that appears or worsens as the limb approaches its target
• Absent at rest; worsens on movement (opposite of Parkinson's resting tremor)
• Due to loss of smooth cerebellar braking of movement

E. Dysarthria (Scanning speech)

• Slurred, irregular, explosive speech
• Loss of coordination of muscles of articulation
• Speech has irregular cadence - "scanning" or "staccato" quality

F. Dysdiadochokinesis

• Inability to perform rapid alternating movements (e.g., pronation/supination of hand)
• Tested by rapid alternating hand tapping

Additional Signs:

• Hypotonia: Decreased resistance to passive movement; pendular reflexes on tendon testing
• Rebound phenomenon (loss of check): When resistance to a movement is suddenly released, the limb overshoots
• Decomposition of movement: Complex movements break down into component parts
• Romberg test: Negative (Romberg positive suggests sensory/proprioceptive ataxia, NOT cerebellar)

Lateralization Rule: