Section 6: Neurology Lecture Notes

Overview

• Focus: Basal Ganglia and Dopaminergic Pathways
• Main Topics: Basal Ganglia Anatomy & Function, Direct & Indirect Pathways, Dopaminergic Pathways

Basal Ganglia

• Role: Responsible for smooth voluntary movements
• Components:
  • Striatum: Caudate and Putamen
  • Lentiform: Putamen and Globus Pallidus
  • Substantia Pars Compacta and Subthalamic Nucleus (STN)

Pathways

• Direct Pathway: Increases movement
• Indirect Pathway: Decreases movement

Anatomical Landmarks

• Sagittal View: Shows caudate, putamen, and thalamus
• Coronal Section: Reveals detailed structure of caudate, thalamus, putamen, Globus Pallidus external and internus

Direct and Indirect Pathways

Direct Pathway

• Function: Excitatory, increases movement
• Process:
  • Motor Cortex → Striatum (Caudate & Putamen) → Globus Pallidus Internus (GPI) → Thalamus (Ventral Lateral Nucleus) → Motor Cortex
  • Neurotransmitter involved: Glutamate (excitatory) and GABA (inhibitory)

Indirect Pathway

• Function: Inhibitory, decreases movement
• Process:
  • Motor Cortex → Striatum → Globus Pallidus Externus (GPE) → Subthalamic Nucleus → Globus Pallidus Internus → Thalamus → Motor Cortex
  • GABA is key in inhibiting movement

Clinical Considerations

Lesions

• Subthalamic Nucleus Damage: Leads to hemiballismus
• Striatum Damage: Leads to Huntington’s Disease
• Unilateral Lesions: Cause contralateral symptoms

Dopaminergic Pathways

• Function: Deliver dopamine to various brain locations
• Major Pathways:
  1. Nigrostriatal Pathway: Substantia → Striatum
     • Stimulates movement via D1 (excitatory) and D2 (inhibitory) receptors
     • Damage leads to Parkinson's Disease
  2. Mesolimbic Pathway: Midbrain (Ventral Tegmental Area) → Limbic System
     • Hyperactivity causes positive symptoms of schizophrenia (delusions, hallucinations)
  3. Mesocortical Pathway: Midbrain → Prefrontal Cortex
     • Hypoactivity causes negative symptoms of schizophrenia (flat affect, anhedonia)
  4. Tuberoinfundibular Pathway: Hypothalamus → Anterior Pituitary
     • Inhibits prolactin release; dysfunction causes hyperprolactinemia

Application Questions

• Parkinson's Disease: Damage to substantia affects movement (slow movement symptoms)
• Schizophrenia Symptoms:
  • Positive symptoms (Mesolimbic)
  • Negative symptoms (Mesocortical)
• Hyperprolactinemia: Linked to dysfunction in Tuberoinfundibular pathway

Conclusion

• Key Understanding: Pathways, their locations, and implications of their dysfunction are crucial for understanding neurological conditions and symptoms.