Notes on Basal Ganglia Lecture

Overview of Basal Ganglia

• Basal Ganglia: Also known as basal nucleus or extrapyramidal nuclei.
• Location: Deep within the white matter of the brain.
• Function: Part of the extrapyramidial motor system for:
  • Regulation of involuntary movements
  • Fine-tuning voluntary movements
  • Maintenance of posture

Structure of Basal Ganglia

• Composed of five pairs of nuclei:
  • Chordae Nucleus
  • Putamen
  • Globus Pallidus
  • Subthalamic Nucleus
  • Substantia
• These nuclei are grouped into broader clusters:
  • Striatum
  • Globus Pallidus
  • Subthalamic Nuclei
  • Substantia Nigra

Detailed Structure and Function

Striatum

• Location: Inside the insular lobe.
• Components: Dorsal striatum (part of basal ganglia) and ventral striatum (part of limbic system).
• Function: Primary input unit, receiving excitatory glutamatergic neurons from the cerebral cortex.
• Neurons: GABAergic, forming direct and indirect pathways to the globus pallidus and subthalamic nuclei.

Globus Pallidus

• Components: Internal segment (GPi) and external segment (GPe).
• Function: Inhibitory, consisting mainly of spontaneously firing GABAergic neurons.
• Pathways:
  • Direct Pathway: From striatum to thalamus.
  • Indirect Pathway: From striatum through GPe to subthalamic nuclei.
• Essential for modulating motor actions.

Subthalamic Nuclei

• Location: Within the subthalamus, functionally part of the basal ganglia.
• Function: Modulation of planned motor movements; contains excitatory glutamatergic neurons.

Substantia Nigra

• Components: Pars compacta and pars reticulata.
• Function:
  • Pars Compacta: Supplies striatum with dopamine.
  • Pars Reticulata: Outputs to thalamus.

Inputs and Outputs

• Afferent Connections:
  • Corticostriatal Pathway: Largest input from the cerebral cortex.
  • Substantia Nigra: Supplies dopamine to striatum.
  • Thalamus: Provides excitatory input via glutamatergic fibers.
• Efferent Fibers:
  • From internal part of globus pallidus and pars reticulata to thalamus and brain stem.

Functions

• Fine-tuning of voluntary movements, preventing unwanted movements, and balancing excitatory input from cerebral cortex.
• Involved in reward processing, motivation, decision making, working memory, and eye movements.

Clinical Anatomy

Parkinson's Disease

• Symptoms: Bradykinesia, resting tremor, postural instability, shuffling gait.
• Cause: Neurodegeneration of dopaminergic neurons in substantia nigra pars compacta.

Huntington's Disease

• Symptoms: Involuntary movements, cognitive degeneration, psychiatric dysfunction.
• Cause: Genetic error in HTT gene with CAG repeat sequence.

Hemiballism

• Symptoms: Hyperkinetic involuntary movements of ipsilateral arm and leg.
• Cause: Lesion in contralateral subthalamic nuclei.

Tourette's Syndrome

• Symptoms: Sudden repetitive uncontrolled movements and vocalizations (ticks).
• Cause: Dysfunction of striatum projections, increased dopaminergic activity.

Summary

• Discussed the basal ganglia's structure, function, and its role in regulating movement.
• Explored clinical cases: Parkinson's, Huntington's, Hemiballism, Tourette's Syndrome.