Basal Ganglia Anatomy and Function
The basal ganglia are essential for the initiation and modulation of movement. Dysfunction leads to either hypokinetic (e.g., Parkinson’s) or hyperkinetic (e.g., Huntington’s) disorders.
1. Anatomy Components
- Striatum: Caudate Nucleus + Putamen.
- Lentiform Nucleus: Putamen + Globus Pallidus.
- Functional Pairings: Subthalamic Nucleus and Substantia Nigra (pars compacta/reticulata).
2. Pathways Overview
| Pathway | Effect on Movement | Net Result |
|---|---|---|
| Direct | Excitatory (via D1 receptors) | Increases movement (“Go”). |
| Indirect | Inhibitory (via D2 receptors) | Decreases movement (“Stop”). |
3. Clinical Pearls
- Parkinson’s Disease: Loss of dopaminergic neurons in the Substantia Nigra pars compacta, leading to increased indirect pathway activity (hypokinetic).
- Huntington’s Disease: Loss of GABAergic neurons in the Striatum (Caudate) leads to decreased indirect pathway activity (hyperkinetic/chorea).
- Hemiballismus: Damage to the Subthalamic Nucleus, usually via lacunar stroke, leads to wild, flailing movements of contralateral limbs.
NEET PG Hint: When you get a question on movement disorders, think about which pathway is being disrupted. Subthalamic nucleus damage = Hemiballismus is an absolute classic test question. Always remember the caudate nucleus is often the first area to show atrophy on imaging in Huntington’s.