LECTURE9.Cerebellum BG_68e69d5a31482db1b4a10e2fe1a942fc

LECTURE 9: CEREBELLUM & BASAL GANGLIA

Anatomy of the Basal Ganglia

  • Components:

    • Caudate nucleus: Important for voluntary movement and learning.

    • Putamen: Involved in motor skills and habits.

    • Globus pallidus: Acts as a major output nucleus for the basal ganglia. Includes lateral and medial regions.

    • Subthalamic nucleus: Plays a role in regulating movements and providing feedback.

    • Substantia nigra: Contains dopaminergic neurons, critical for movement control and reward processes.

    • Striatum: Comprised of the caudate and putamen, involved in coordinating movement.

    • Thalamus: Relays information between the basal ganglia and the cortex.

    • Pons: Connects the cerebellum to the brainstem, influencing motor control.

    • Spinal cord: Transmits motor commands from the brain to the body.

Anatomy of the Cerebellum

  • Deep Cerebellar Nuclei:

    • Dentate nucleus: Largest nucleus, involved in planning and coordinating voluntary movements.

    • Interposed nuclei: Include embolland and globose nuclei, contribute to limb coordination.

    • Fastigial nucleus: Plays a key role in balance and coordination of posture.

CEREBELLUM

  • General Overview:

    • Size: 10% of the brain's volume but contains more neurons than the cerebrum.

    • Functions:

      • Responsible for fine motor control, balance, coordination, and learning new motor skills.

      • Plays a role in cognitive functions, such as attention and language processing.

Cerebellar Physiology Principles

  • Five Physiological Principles:

    1. Acts in advance of sensory feedback from movement: Ensures smooth execution of movements.

    2. Relies on internal body models: Compares sensory inputs with motor commands to adjust movements effectively.

    3. Critical role in motor and perceptual timing: Essential for tasks that require precise timing, such as playing a musical instrument.

    4. Essential for adapting and learning motor skills: Allows for refinement of movements based on previous experiences.

    5. Extensive connectivity to nonmotor areas: Indicates that cerebellum also plays a role in cognitive functions and emotional processing.

Damage and Function

  • Cerebellar Damage:

    • Impacts motor control, leading to abnormalities such as ataxia (lack of voluntary coordination of muscle movements) and dysmetria (overshooting or undershooting intended movements) while highlighting the cerebellum's role in coordination.

CEREBELLAR ANATOMY

  • Fissures and Nuclei:

    • Dorsal View: Primary fissure, Hemispheres, Dentate, and Interposed nuclei.

    • Ventral View: Cerebellar peduncles (Superior, Middle, Inferior) facilitate communication between the cerebellum and the brain.

Functional Regions of the Cerebellum

  • Cerebrocerebellum:

    • Meaning: Involved in planning and timing of movements, including those related to speech and fine motor skills.

  • Spinocerebellum:

    • Meaning: Monitors body and limb position and adjusts movements based on sensory feedback.

  • Vestibulocerebellum:

    • Meaning: Maintains balance and eye movements, influencing posture and spatial orientation.

Longitudinal Zones in the Cerebellum

  • Different zones control various movements based on their longitudinal divisions (Cerebrocerebellum, Spinocerebellum, Vestibulocerebellum).

CEREBELLAR CONNECTIONS

  • Connections to the Cerebrum:

    • Cortical-Cerebellar Circuit:

      • First Order: Cerebral cortex

      • Second Order: Thalamus

      • Third Order: Cerebellum

  • Repeated Functional Units: Electrophysiological studies emphasize anticipation and signaling speed in motor functions.

Microcircuit Architecture

  • Functional Layers in Cerebellar Cortex:

    • Granular Layer: Contains granule cells that integrate inputs.

    • Purkinje Layer: Composed largely of Purkinje cells, key in outputting inhibitory signals.

    • Molecular Layer: Contains connections between neurons, allowing for complex processing.

  • Key cells include Granule cells, Purkinje cells, and Golgi cells.

ROLE OF CEREBELLUM IN MOTOR LEARNING

  • The capacity for plasticity allows the cerebellum to adapt and refine motor responses through learning processes, facilitating both motor skill acquisition and the adjustment of actions based on feedback.

THE BASAL GANGLIA

  • Overview and Function:

    • Integration of motor control with cognitive and motivational processes, influencing habit formation and reward learning.

    • Key components include Caudate nucleus, Putamen, Globus pallidus, Subthalamic nucleus, and Substantia nigra.

  • Representative Circuitry of Basal Ganglia:

    • Internal circuitry illustrates interaction among cortical inputs and basal ganglia outputs.

  • Reentrant Loops:

    • A key principle of basal ganglia function highlighting spatially segregated gradient representation within the brain's circuitry, enabling refined motor planning and execution.

  • Functional Regions:

    • Differentiated regions in the striatum play roles in sensory, motor, and associative functions, indicating the complexity of basal ganglia involvement in behavior, including the reward pathways and cognitive activities.