131. Basal Ganglia – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• The basal ganglia are interconnected subcortical nuclei that regulate the planning, initiation, selection, and coordination of voluntary movements. They influence posture through brainstem pathways but do not directly control spinal motor neurons. Input comes mainly from the cerebral cortex, and output returns to the cortex via the thalamus.
• The major components are caudate nucleus, putamen, and globus pallidus. The striatum consists of the caudate nucleus and putamen and is the major input region. The lentiform nucleus is formed by the putamen and globus pallidus. The substantia nigra and subthalamic nucleus are functionally associated with the basal ganglia.
• The major input arises from the cerebral cortex through the striatum. The major output originates from the internal segment of the globus pallidus and reaches the thalamus before returning to the motor cortex. This motor loop (cortex → striatum → globus pallidus interna → thalamus → cortex) selects appropriate movements and suppresses unwanted ones.
• Important internal connections include the nigrostriatal pathway (dopaminergic), striatonigral pathway (gamma aminobutyric acid-mediated), and projections from the subthalamic nucleus. Degeneration of the nigrostriatal pathway causes Parkinson disease, whereas dysfunction of the striatonigral pathway is associated with Huntington disease.
• The direct pathway facilitates voluntary movement by disinhibiting the thalamus and increasing motor cortical activity. The indirect pathway suppresses unnecessary movements by increasing inhibitory output from the globus pallidus interna to the thalamus. Normal movement depends on a balance between these two pathways. Dopamine enhances the direct pathway and inhibits the indirect pathway, whereas acetylcholine exerts the opposite effect.
• Major functions of the basal ganglia include:
  • Planning and programming voluntary movements.
  • Initiating desired motor activity and suppressing unwanted movements.
  • Regulating muscle tone and posture.
  • Coordinating associated movements such as arm swinging during walking.
  • Contributing to motor learning, habit formation, and action selection.
• Parkinson disease results from degeneration of dopaminergic neurons in the substantia nigra pars compacta. Features include akinesia, bradykinesia, masked facies, resting tremor (4–6 Hz), lead-pipe and cogwheel rigidity, and a festinating gait with stooped posture and shuffling steps. Treatment includes levodopa with a peripheral decarboxylase inhibitor, dopamine agonists, monoamine oxidase-B inhibitors, anticholinergic drugs, deep brain stimulation, and rehabilitation.
• Huntington disease is an autosomal dominant disorder caused by CAG repeat expansion in the HTT gene. Degeneration of gamma aminobutyric acid-releasing neurons in the striatum causes chorea, cognitive decline, psychiatric symptoms, and dysarthria. Treatment is supportive and includes rehabilitation and genetic counseling.
• Other basal ganglia disorders include:
  • Ballism/Hemiballism: Violent flinging movements due to subthalamic nucleus lesions.
  • Athetosis: Slow writhing movements due to striatal lesions.
  • Chorea: Rapid irregular involuntary movements, commonly associated with caudate nucleus degeneration.