Basal Ganglia Lecture Notes

Introduction

• Topics Covered: Basic anatomy, basic function, pathways (direct, indirect, nigrostriatal), clinical relevance of basal ganglia lesions

Basic Anatomy of Basal Ganglia

• Main Components:

  • Caudate Nucleus
  • Putamen
  • Globus Pallidus
    • Internal Part
    • External Part
  • Thalamus
    • Part of Basal Ganglia: Ventral Anterior and Ventral Lateral Nucleus
  • Subthalamic Nuclei
  • Substantia Nigra
    • Parts: Zona Compacta and Zona Reticularis

• Terminology:

  • Striatum: Caudate nucleus + Putamen
  • Lentiform Nucleus: Putamen + Globus pallidus

Basic Function

• Role in Motor Function:

  • Start movement
  • Stop unwanted movement
  • Modulate motor movement

• Cortical Areas Involved:

  • Primary Motor Cortex
  • Premotor Cortex
  • Primary Somatosensory Cortex

Pathways

Direct Pathway

• Purpose: Increase or stimulate motor activity
• Pathway: Cortex → Striatum → Globus Pallidus Internus → Thalamus (Ventral Anterior and Ventral Lateral) → Cortex
• Neurotransmitters:
  • Glutamate: Stimulatory neurotransmitter
  • GABA: Inhibitory neurotransmitter
• Mechanism:
  • Cortex releases glutamate stimulating striatum → Striatum releases GABA inhibiting globus pallidus internus → Less GABA to thalamus → Disinhibition of thalamus → Increased cortical stimulation → Increased motor activity

Indirect Pathway

• Purpose: Decrease motor activity, particularly unwanted movements
• Pathway: Cortex → Striatum → Globus Pallidus Externus → Subthalamic Nucleus → Globus Pallidus Internus → Thalamus → Cortex
• Neurotransmitters:
  • Glutamate: Stimulatory
  • GABA: Inhibitory
• Mechanism:
  • Cortex stimulates striatum → Striatum inhibits globus pallidus externus → Disinhibition of subthalamic nucleus → Stimulation of globus pallidus internus → Inhibition of thalamus → Decreased cortical stimulation → Decreased motor activity

Nigrostriatal Pathway

• Purpose: Modulate activity of direct and indirect pathways, amplifying motor activity

• Influence on Direct Pathway:

  • D1 Receptors: Stimulatory, enhancing motor activity
  • Mechanism: Dopamine from substantia nigra stimulates striatum → Enhances direct pathway → Increases motor activity
  • Clinical Relevance: Parkinson's disease results from degeneration impacting this pathway

• Influence on Indirect Pathway:

  • D2 Receptors: Inhibitory, decreasing unwanted motor activity
  • Mechanism: Dopamine inhibits striatum → Reduces indirect pathway's suppression of movement

Clinical Relevance

• Parkinson's Disease: Difficulty initiating movements due to damage in direct pathway
• Huntington's Disease & Wilson's Disease: Unwanted motor movements from damage to indirect pathways
• Extrapyramidal Symptoms (e.g., from antipsychotics): Include tardive dyskinesia, akathisia

Conclusion

• Summary: Covered anatomy, function, pathways, and clinical importance of basal ganglia
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Study Tip: Understand the role of neurotransmitters and pathways in modulating motor activity for better grasp of clinical conditions related to the basal ganglia.