Makindo Medical Notes

Related Subjects: |Brain Herniation syndromes |Haemorrhagic stroke |Traumatic Head/Brain Injury |Acute Hydrocephalus |Epidural Haematoma |Subdural haematoma |Basic Neuroscience |Medulla Oblongata |Midbrain |Pons |Caudate Nucleus |Putamen and Globus Pallidus |Cerebral Cortex |Internal Capsule |Cavernous sinus |Basal Ganglia

🧠 Basal Ganglia

The basal ganglia are a group of interconnected subcortical nuclei located deep within the cerebral hemispheres. They play a crucial role in motor control, procedural learning, habit formation, emotions, and smooth voluntary movement. Key components: caudate nucleus, putamen, nucleus accumbens, globus pallidus, subthalamic nucleus, and substantia nigra.

• Putamen & Globus Pallidus:
  • Putamen = initiation & control of voluntary movements ⚡
  • Globus pallidus → GPe (external) & GPi (internal, major output → thalamus).
  • Together they form the lentiform nucleus.
• Caudate Nucleus:
  • C-shaped, wraps around lateral ventricles.
  • Involved in cognition, feedback, & goal-directed behaviour 🎯.
  • Degeneration in Huntington’s disease → chorea 💃.
• Nucleus Accumbens (Ventral Striatum):
  • Centre of reward & motivation ❤️.
  • Strongly modulated by dopamine from the VTA.
• Subthalamic Nucleus (STN):
  • Part of indirect pathway 🚫 unwanted movement.
  • Damage → hemiballismus (flinging movements) 🤾.
• Substantia Nigra:
  • 🌑 SNc: dopamine production → striatum (lost in Parkinson’s disease).
  • ⚫ SNr: output nucleus → inhibitory projections to thalamus/brainstem.

🔗 Connections of the Basal Ganglia

• Input nuclei: caudate, putamen, nucleus accumbens → receive glutamatergic input from cortex.
• Output nuclei: GPi & SNr → send GABAergic (inhibitory) signals to thalamus → motor cortex.
• ➡️ Direct Pathway:
  • “GO” pathway ✅ → facilitates movement.
  • Striatum inhibits GPi/SNr → ↓ thalamic inhibition → ↑ motor cortex activity.
• ⛔ Indirect Pathway:
  • “STOP” pathway ❌ → suppresses unwanted movement.
  • Striatum inhibits GPe → disinhibits STN → STN excites GPi → ↑ thalamic inhibition → ↓ motor cortex activity.
• 🎭 Dopamine modulation:
  • D1 receptors (direct pathway) = excitatory → promotes movement.
  • D2 receptors (indirect pathway) = inhibitory → also promotes movement.
  • Loss of SNc dopamine in Parkinson’s disease → imbalance → bradykinesia & rigidity.

⚙️ Functions of the Basal Ganglia

• 🎯 Motor control: smooth execution of voluntary movements.
• 🔁 Habit formation & procedural memory.
• ❤️ Reward & motivation (nucleus accumbens, ventral striatum).
• 🧩 Cognitive functions: decision-making, planning, & sequencing actions.

🏥 Clinical Relevance

• 🟤 Parkinson’s disease: loss of dopamine neurons in SNc → tremor, rigidity, bradykinesia, postural instability. Managed with L-DOPA, dopamine agonists.
• 🔵 Huntington’s disease: degeneration of striatal GABAergic neurons (esp. caudate) → chorea + cognitive decline.
• 🌀 Dystonia: abnormal contractions from BG dysfunction.
• 🤾 Hemiballismus: STN lesion → violent flinging movements.
• 🗣️ Tourette’s syndrome: BG-thalamocortical dysfunction → motor & vocal tics.