Basal Ganglia Lecture

Jul 25, 2024

Basal Ganglia Lecture Notes

Introduction

  • Topic: Basal Ganglia
  • Key Areas: Anatomy, Function, Pathways (Direct, Indirect, Nigrostriatal), Clinical Relevance

Basic Anatomy of the Basal Ganglia

Orientation and Components

  • Coronal Section View
  • Main Components:
    • Caudate Nucleus
    • Putamen
    • Globus Pallidus (Internal/External)
    • Thalamus
    • Subthalamic Nucleus
    • Substantia Nigra (Zona Compacta/Zona Reticularis)

Specific Terminology

  • Striatum: Caudate Nucleus + Putamen
  • Lentiform Nucleus: Putamen + Globus Pallidus
  • Thalamus involvement: Ventral Anterior (VA) and Ventral Lateral (VL) nuclei

Function of the Basal Ganglia

Motor Function

  • Coordinated by the cerebral cortex (Primary Motor Cortex, Premotor Cortex, Primary Somatosensory Cortex)
  • Key Roles: Start Movement, Stop Movement, Modulate Movement
  • Communication with the Basal Ganglia to modify motor plans before sending to muscles

Pathways of the Basal Ganglia

1. Direct Pathway

  • Purpose: Increase or stimulate motor activity
  • Flow: Cortex → Striatum → Globus Pallidus Internus → Thalamus (VA/VL) → Cortex
  • Neurotransmitters:
    • Glutamate (Excitatory) from Cortex to Striatum
    • GABA (Inhibitory) from Striatum to Globus Pallidus Internus
    • GABA from Globus Pallidus Internus to Thalamus (VA/VL)
  • Effect: Increased stimulation of the thalamic nuclei, leading to increased motor activity

2. Indirect Pathway

  • Purpose: Decrease or inhibit unwanted motor activity
  • Flow: Cortex → Striatum → Globus Pallidus Externus → Subthalamic Nucleus → Globus Pallidus Internus → Thalamus (VA/VL) → Cortex
  • Neurotransmitters:
    • Glutamate from Cortex to Striatum
    • GABA from Striatum to Globus Pallidus Externus
    • GABA from Globus Pallidus Externus to Subthalamic Nucleus
    • Glutamate from Subthalamic Nucleus to Globus Pallidus Internus
    • GABA from Globus Pallidus Internus to Thalamus (VA/VL)
  • Effect: Inhibition of the thalamic nuclei, leading to decreased motor activity

3. Nigrostriatal Pathway

  • Purpose: Modulate both Direct and Indirect Pathways
  • Receptors and Effects:
    • D1 Receptors (Direct Pathway): Stimulatory
    • D2 Receptors (Indirect Pathway): Inhibitory
  • Pathway Influence:
    • Direct Pathway: Amplifies motor activity by stimulating striatum neurons
    • Indirect Pathway: Reduces unwanted motor activities by inhibiting striatum neurons

Neurotransmitters Explained

GABA

  • Type: Inhibitory
  • Receptors: GABA-A, GABA-B, GABA-C
  • Mechanism: Ligand-gated ion channels, hyperpolarization (IPSP)

Glutamate

  • Type: Stimulatory
  • Mechanism: Ligand-gated ion channels, depolarization (EPSP)

Dopamine

  • D1 Receptors: Stimulatory (Increased cyclic AMP)
  • D2 Receptors: Inhibitory (Decreased cyclic AMP)

Clinical Relevance

Disease Associations

  • Parkinson’s Disease: Damage to the Direct Pathway/Nigrostriatal Pathway (difficulty initiating movement)
  • Huntington’s Disease: Damage to the Indirect Pathway (unwanted movements)
  • Wilson’s Disease: Copper buildup affects basal ganglia (hepatolenticular degeneration)
  • Syndenham’s Chorea: Rheumatic fever affecting basal ganglia
  • Extrapyramidal Syndrome: Side effects of antipsychotics (issues with D2 receptors)

Conclusion

  • Covered: Anatomy, Function, Pathways, Clinical Relevance
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