Notes on the Cerebellum

Introduction to the Cerebellum

• Translation: "Cerebellum" means "little brain" not due to size but appearance similar to the human cerebrum.
• Functions:
  • Coordinates and adjusts voluntary movements.
  • Major role in:
    • Posture
    • Balance
    • Maintenance of muscle tone
    • Coordinating skilled voluntary motor activities (e.g., riding a bicycle, walking a tightrope).
• Communication: Constant interaction with the cerebral cortex and other structures in the nervous system.

Anatomy of the Cerebellum

• Location: Sits in the posterior cranial fossa, covered by the tentorium cerebelli.
• Surroundings: Anterior to the cerebellum are the fourth ventricle, pons, and medulla oblongata.
• Structure:
  • Two hemispheres connected by a narrow ridge called the vermis.
  • Divided into three lobes:
    • Anterior lobe
    • Posterior lobe
    • Flocculonodular lobe.

Lobes and Functional Regions

• Anterior Lobe:
  • Functionally the "spinal cerebellum".
  • Regulates muscle tone and adjusts ongoing movements.
• Posterior Lobe:
  • Functionally the "cerebrocerebellum" or "pontocerebellum".
  • Largest part, involved in planning and programming skilled movements.
  • Contains the primary fissure, separating it from the anterior lobe.
• Flocculonodular Lobe:
  • Functionally the "vestibulocerebellum".
  • Responsible for balance and posture.

Internal Structure

• Peduncles:
  • Bundles of white matter connecting the cerebellum to the brainstem:
    • Superior: connects to midbrain.
    • Middle: connects to pons.
    • Inferior: connects to medulla oblongata.
• Cortex:
  • Folds create ridges (Folia) with sulci in between, increasing surface area.
  • Contains an external gray matter layer (cerebellar cortex) and subcortical white matter.
• Deep Cerebellar Nuclei:
  • Clusters of gray matter in subcortical white matter:
    • Dentate
    • Emboliform
    • Globose
    • Fastigial.

Functional Zones of the Cerebellar Cortex

• Lateral Zone:
  • Sends signals to dentate nucleus for planning and programming movements.
• Intermediate Zone:
  • Sends signals to interposed nuclei (globus and emboliform) for motor execution.
• Median Zone:
  • Sends signals to the fastigial nucleus, modulating motor execution.

Afferent Pathways to the Cerebellum

• From the Spinal Cord:
  • Ventral (Anterior) Spinal Cerebellar Pathway:
    • Carries proprioceptive info, crosses over (double crosser).
  • Dorsal (Posterior) Spinal Cerebellar Pathway:
    • Carries proprioceptive info from trunk/lower limbs, ascends ipsilaterally.
  • Cuneocerebellar Pathway:
    • Carries proprioceptive info from upper limbs, ipsilateral pathway.
• From the Cerebral Cortex:
  • Cortico-Ponto-Cerebellar Pathway:
    • Relays motor commands, synapses at pontine nuclei.
  • Cerebral Olivocerebellar Pathway:
    • Involves inferior olivary nuclei for coordination.
  • Cerebral Reticulocerebellar Pathway:
    • From sensory motor regions to modulate movements.
• Vestibulocerebellar Pathway:
  • Involved in maintaining balance and posture via sensory input from inner ear.

Efferent Pathways from the Cerebellum

• Vestibular Pathway:
  • Regulates extensor muscle tone, maintains posture.
• Dentatothalamic Pathway:
  • Modifies ipsilateral motor activity, influences motor cortex.
• Globose-Emboliform-Rubro Pathway:
  • Affects proximal flexor musculature of upper limb.
• Fastigial-Reticular Pathway:
  • Regulates muscle tone and posture through reticular formation.

Summary

• Overall Role:
  • Cerebellum integrates and processes information to maintain posture, balance, and coordinate movements.
• Anatomical Summary:
  • Located in posterior cranial fossa, divided into lobes and functional zones.
  • Connected by peduncles to the central nervous system.
  • Involves complex pathways for afferent input and efferent output.