Cerebellum Overview

Cerebellum Study Notes

Thomas J. Perrault Jr., PhD
Asst. Professor of General Surgery
Wake Forest School of Medicine
Email: Thomas.Perrault@wfusm.edu
Office: 4430
Lauren Fowler, PhD
Professor of Neuroscience
Department of Physiology and Pharmacology
Wake Forest School of Medicine
Email: lafowler@wakehealth.edu

Session Objectives

  • Identify external features of cerebellum and their functions: Understanding the anatomy helps in recognizing functional aspects.

  • Describe functional divisions of the cerebellum: Key areas of functionality such as the vermis and lateral hemispheres.

  • Describe layers of the cerebellar cortex: Distinction between molecular, Purkinje, and granular layers.

  • Identify afferents and efferents to the cerebellum and their pathways: Understanding the neural connections and circuits vital for its function.

  • Identify clinical conditions associated with the cerebellum: Link between cerebellar dysfunction and neurological disorders.

  • Compare and contrast cerebellar signs and how to assess them: Understanding standardized tests for cerebellar function.

Clinical Correlations

Key Conditions

  • Chiari Malformation (I and II): A structural defect in the cerebellum that affects its positioning.

    • Type I: Congenital, asymptomatic or mild symptoms.

    • Type II: More severe, involves both cerebellar tonsils and the medulla, symptomatic.

  • Cerebellar Symptoms:

    • Ataxia: Loss of muscle coordination affecting balance, speech, and motor skills. It results from the cerebellum's inability to finely tune motor commands and integrate sensory input.

    • Dysarthria: Ataxia affecting the larynx, resulting in impaired language production. The rhythm and articulation are often affected.

    • Scanning speech: Syllabic enunciation leading to speech disfluency, e.g., “the British parliament” becomes “the Brit-tish Par-la-ment”, indicating a difficulty in smoothly coordinating speech movements..

    • Intention tremor: Occurs when purposeful movement is attempted. Reflecting a failure of the cerebellum to damp oscillatory movements

    • Hypotonia: Characterized by low muscle tone. This occurs because the cerebellum normally helps maintain baseline muscle tone.

    • Dysdiadochokinesia: Difficulty performing rapid alternating movements. This indicates impaired coordination and sequencing of movements.

    • Nystagmus: Involuntary eye movements with fast phases toward the lesion.

    • Dysmetria: Inaccurate range or timing of movements. This demonstrates an inability to properly gauge the distance or force required for a movement.

The Cerebellum

  • Anatomy: Firmly nestled in the posterior cranial fossa.

  • Functions:

    • Coordinates movements.

    • Controls posture and balance.

    • Manages fine motor skills.

    • Plays a role in motor learning.

Anatomical Structures

Tentorium Cerebelli:

  • Dura mater acting as a 'tent' separating cerebellum from the inferior portion of occipital lobes.

Main Features of the Cerebellum

  • 3 Main Fissures: Primary, horizontal, posterolateral.

  • 3 Lobes:

    • Anterior: The anterior lobe is responsible for regulating voluntary movement and plays a key role in posture and balance.

    • Posterior/middle: The posterior lobe is involved in the coordination of movement and fine motor skills, integrating sensory information to ensure smooth execution of tasks.

    • Flocculonodular: The flocculonodular lobe is primarily responsible for maintaining equilibrium and balance, serving as a crucial component for coordinating eye movements in relation to head movements.

  • 3 Peduncles:

    • Superior: Primarily efferent, connecting the cerebellum to the midbrain and thalamus.

    • Middle: Mostly afferent, linking the cerebellum with the pons, carrying sensory information about the body’s position and movement.

    • Inferior: Both afferent and efferent, connecting the cerebellum to the medulla oblongata and spinal cord.

  • 3 Cellular Layers:

    • Deep cerebellar nuclei: These are the primary output structures of the cerebellum, responsible for relaying processed information to other brain regions, including the motor cortex and brainstem, which are crucial for coordinating voluntary movements.

    • Arbor vitae: This is the tree-like arrangement of white matter within the cerebellum, providing a pathway for communication between the cerebellar cortex and the deeper structures, facilitating the integration of sensory and motor information for balance and coordination.

    • Cerebellar cortex: The highly folded outer grey matter layer, responsible for processing information through its distinct cortical layers.

  • 3 Cortical Layers:

    • Molecular layer: This outermost layer is composed of a dense network of stellate and basket cells, playing a crucial role in the integration of inputs from various sources and influencing the output of Purkinje cells.

    • Purkinje layer: This middle layer contains the large Purkinje cells, which are essential for the output of motor coordination signals to the deep cerebellar nuclei.

    • Granular layer: This innermost layer comprises densely packed granule cells that receive inputs from the mossy fibers and send their axons to the molecular layer, where they form synapses with the parallel fibers.

  • 3 Arteries: Superior cerebellar artery (SCA), posterior inferior cerebellar artery (PICA), anterior inferior cerebellar artery (AICA).

Basic Anatomical Reference

  • Components:

    • Midbrain tectum: The roof of the midbrain, involved in visual and auditory reflexes, consisting of the superior and inferior colliculi.

    • Cerebral aqueduct: A narrow channel connecting the third and fourth ventricles of the brain, playing a crucial role in the flow of cerebrospinal fluid.

    • Clivus: A bony structure located at the base of the skull, serving as a support for the brainstem and part of the pons.

    • Pons: A prominent structure located above the medulla and below the midbrain, responsible for relaying messages between the cerebellum and the cerebrum, as well as regulating functions such as sleep, respiration, and facial sensations.

    • Medulla (rostral and caudal): The medulla is the lower half of the brainstem, crucial for autonomic functions such as heartbeat, breathing, and blood pressure regulation, with rostral referring to the upper part closer to the pons, and caudal indicating the lower part near the spinal cord.

    • Spinal cord: Extends from the medulla, transmitting motor and sensory information to and from the brain. Provides proprioceptive input to the cerebellum.

    • Fourth ventricle: Located between the cerebellum and the pons, the fourth ventricle is a fluid-filled cavity that contains cerebrospinal fluid, helping to cushion the brain and circulate nutrients.

    • Anterior medullary velum: A thin sheet of tissue that covers the upper part of the fourth ventricle, facilitating communication between the cerebellum and other brain regions.

Cerebellar Surface Features

  • Folia: Folds in the cerebellum contributing to its surface area.

Functional Divisions of the Cerebellum

Vermis

  • Function: Control of trunk movements.

  • Damage outcome: Results in a truncal tremor (unsteadiness of the body and head) and ataxic gait (wide-based, unsteady walking pattern).

  • Spinocerebellar Tract: Pathways transporting proprioceptive and cutaneous information to the cerebellum.

Hemispheres

  • Cerebrocerebellum: Integrates information from the contralateral cerebrum.

  • Function: Manages limb movements.

  • Damage consequences: Results in ataxic limbs, dysarthria, and intention tremors.

Flocculus/Nodulus

  • Vestibulocerebellum: Gathers information from vestibular nuclei.

  • Consequences of damage: Can cause vestibular symptoms such as falling, nystagmus, and vertigo.

Cerebellar Peduncles

Types and Functions

  • Superior Cerebellar Peduncle:

    • Function: Carries efferent information from the cerebellum to motor areas of the thalamus.

  • Middle Cerebellar Peduncle:

    • Function: Transmits contralateral motor information to the cerebellum from the brain.

  • Inferior Cerebellar Peduncle:

    • Function: Carries ipsilateral proprioceptive information and vestibular sense data.

Cell Layers in the Cerebellar Cortex

Layers and Functionality

  • Molecular Layer:

    • Contains inhibitory interneurons (GABA) including stellate and basket cells.

    • Features parallel fibers (GLUT) that connect with Purkinje cell dendrites.

  • Purkinje Layer:

    • Contains the bodies of Purkinje cells which project efferent signals.

  • Granular Layer:

    • Houses granule cells and interneurons (Golgi cells).

Input and Output Mechanisms

  • Input:

    • Climbing fibers: Originating from the inferior olivary nucleus, they directly connect to Purkinje cells.

    • Mossy fibers: Input received from multiple sources (vestibular nuclei, spinal cord, and pons) to relay to granule cells, and then to Purkinje cells.

  • Output: Only projections that exit the cerebellar cortex are from Purkinje cells, releasing GABA.

Functional Role of the Cerebellum

  • Coordination: Integrates sensory feedback to adjust motor commands.

  • Neural Pathways: Affects the contralateral motor cortex while influencing the ipsilateral body by connecting to various brain regions without directly targeting spinal motor neurons.

  • Decussations: Important points where neuronal fibers cross ensuring coordinated function between hemispheres, e.g., decussation of pyramids.

Clinical Assessment of Cerebellar Function

Neurological Exam Techniques

  • Limb Ataxia:

    • Finger to nose test: Assesses dysmetria.

    • Heel to shin test: Checks coordination and precision in limb movement.

  • Rapid Alternating Movements:

    • Foot Tapping: Tests rhythmic coordination.

    • Alternating Hand Movement: Assesses agility and coordination (dysdiadochokinesia).

  • Truncal Ataxia:

    • Romberg Test: Evaluates proprioception by observing postural stability.

    • Truncal Sway (Titubation): Observing instability of the trunk.

  • Gait Assessment: Look for unsteady, ataxic, and wide-based walking patterns.

Clinical Applications

  • Impact of lesions on cerebellar functionality:

    • Flocculonodular lobe lesions induce disequilibrium.

    • Cerebropontine connections lesions lead to hypotonia and intention tremor.

    • Anterior lobe lesions result in ataxia, often seen with specific tumors in children.

Review and Practice

Recap of Key Concepts

  • Symptoms can indicate damage to specific cerebellar areas, pathways, or vasculature.

  • Cerebellar damage leads to ipsilateral deficits and can provide insights into the lesion's side and location.

  • Review the types of cerebellar cells and their connections.

Supplemental Materials

  • For more in-depth understanding, formative practice problems available on Canvas.

  • Queries can be sent to Thomas.Perrault@wfusm.edu.

Vascular Supply of the Cerebellum

  • Arteries:

    • Superior Cerebellar Artery (SCA)

    • Anterior Inferior Cerebellar Artery (AICA)

    • Posterior Inferior Cerebellar Artery (PICA)

Functional Regions of the Cerebellum

Operational Characteristics

  • Hemisphere (lateral):

    • Input: Cerebrocerebellar.

    • Function: Coordination and planning of peripheral movements.

  • Vermis:

    • Input: Spinocerebellar.

    • Function: Maintains axial equilibrium.

  • Flocculonodular Lobe:

    • Input: Vestibulocerebellar.

    • Function: Balance and coordination relating to the vestibular system.

Cell Types in Cerebellar Structure

Key Cell Types

  • Candelabrum Cell

  • Basket Cell

  • Bergmann Glia

  • Stellate Cell

  • Purkinje Cell

  • Granule Cell

  • Golgi Cell

  • Unipolar Brush Cell

  • Output Mechanisms: Purkinje cells provide primary output from the cortical layers to the deep nuclei and further into the motor system.