Anatomy and Physiology of the Cerebellum

Cerebellum: Overview

Introduction

The cerebellum is the largest part of the hindbrain and plays a crucial role in motor control, coordination, and balance. It is located in the posterior cranial fossa, behind the pons and medulla, and separated from the occipital lobe by the tentorium cerebelli.

• Weight: About 150 grams in adults.

• Shape: Ovoid, constricted in the middle.

• Structure: Composed of an outer gray cortex and inner white matter, with four pairs of deep cerebellar nuclei embedded within.

Location and Relations

• Situated in the posterior cranial fossa.

• Separated from the pons and medulla by the 4th ventricle.

• Above, separated from the occipital lobe by the tentorium cerebelli.

External Features of the Cerebellum

Parts and Surfaces

• Three parts: Two cerebellar hemispheres joined by the median vermis.

• Two surfaces:

  • Superior surface: Convex.

  • Inferior surface: Notched.

Notches and Borders

• Two notches:

  • Anterior cerebellar notch: Wide and shallow; lodges pons and medulla.

  • Posterior cerebellar notch: Narrow and deep.

• Two borders:

  • Anterolateral border

  • Posterior border

Fissures

The cerebellum is subdivided into numerous small parts by parallel fissures. Each fissure cuts the vermis and both hemispheres.

• Primary fissure: Separates the anterior lobe from the middle lobe.

• Horizontal fissure: Separates the superior from the inferior surface.

• Postero-lateral fissure: Separates the middle from the flocculo-nodular lobe on the inferior surface.

Lobes of the Cerebellum

Anatomical Lobation

• Anterior lobe: Lies on the superior surface in front of the primary fissure.

• Middle lobe (Posterior lobe): Largest lobe, lies between the primary fissure (superior surface) and postero-lateral fissure (inferior surface).

• Flocculo-nodular lobe: Smallest lobe, lies on the inferior surface in front of the postero-lateral fissure.

Functional Lobes

• Archicerebellum: Maintains equilibrium of the body.

• Paleocerebellum: Regulates muscle tone.

• Neocerebellum: Coordinates skilled movement.

Gray Matter of the Cerebellum

Components

• Cerebellar cortex

• Cerebellar nuclei: Four pairs:

  • Dentate nucleus

  • Emboliform nucleus

  • Globose nucleus

  • Fastigial nucleus

Cerebellar Peduncles

Connections to Brainstem

• Superior cerebellar peduncle: Connects to the midbrain.

• Middle cerebellar peduncle: Connects to the pons.

• Inferior cerebellar peduncle: Connects to the medulla oblongata.

Functions of the Cerebellum

• Controls the same side of the body (ipsilateral control).

• Regulates muscle tone, posture, and equilibrium.

• Coordinates skilled voluntary movements.

Blood Supply of the Cerebellum

Main Arteries

• Superior cerebellar artery (SCA): Branch of the basilar artery.

• Anterior inferior cerebellar artery (AICA): Branch of the basilar artery.

• Posterior inferior cerebellar artery (PICA): Branch of the vertebral artery.

Cerebellar Lesions and Clinical Signs

Effects of Lesions

• Ataxia: Drunken gait, unsteady walking.

• Hypotonia: Weak muscle tone.

• Adiadochokinesia: Inability to perform rapid, alternating movements.

• Intentional tremor: Tremor during voluntary movement.

• Scanning speech (dysarthria): Disrupted speech pattern.

• Nystagmus: Uncontrollable movements of the eyes.

• Asthenia: Weakness, lack of energy, loss of strength.

Symptoms of Asthenia

• Fever

• Fatigue

• Muscle cramps

• Pain in joints

Summary Table: Cerebellar Lobes and Functions

Lobe	Anatomical Location	Functional Role
Anterior lobe	Superior surface, in front of primary fissure	Equilibrium (Archicerebellum)
Middle (Posterior) lobe	Between primary and postero-lateral fissures	Muscle tone regulation (Paleocerebellum)
Flocculo-nodular lobe	Inferior surface, in front of postero-lateral fissure	Coordination of skilled movement (Neocerebellum)

Summary Table: Cerebellar Nuclei

Nucleus	Location	Main Function
Dentate	Lateral cerebellar hemisphere	Planning and initiation of voluntary movements
Emboliform	Intermediate zone	Regulation of limb movements
Globose	Intermediate zone	Regulation of limb movements
Fastigial	Vermis	Balance and posture

Summary Table: Cerebellar Peduncles

Peduncle	Connection	Main Function
Superior	Midbrain	Output from cerebellum to cerebral cortex
Middle	Pons	Input from cerebral cortex to cerebellum
Inferior	Medulla oblongata	Input from spinal cord and medulla to cerebellum

Key Equations

• Motor Coordination: $\text{Cerebellar Output} = \text{Cerebellar Cortex} \rightarrow \text{Deep Nuclei} \rightarrow \text{Motor Pathways}$

Additional info:

• The cerebellum is present in all vertebrates and is essential for motor coordination across species.

• Lesions of the cerebellum typically produce ipsilateral symptoms due to the double-crossing of cerebellar pathways.