Overview
This lecture covers the anatomy, circuits, and clinical relevance of the basal ganglia, focusing on its role in motor control and notable neurologic disorders, followed by exam-style questions and answers.
Anatomy of the Basal Ganglia
- The basal ganglia consist of the globus pallidus, putamen, and caudate nucleus, found deep within the cerebral hemispheres.
- The thalamus is located medially and connects via interthalamic adhesion.
- The internal capsule, with anterior, genu, posterior, and retrolenticular parts, is lateral to the thalamus.
- Globus pallidus has internal and external segments; together with putamen, they form the lentiform nucleus.
- The caudate nucleus is C-shaped with head, body, and tail (ending at the amygdaloid body).
- Together, the caudate nucleus, putamen, and globus pallidus are termed basal ganglia.
- Caudate and putamen together are called striatum; putamen and globus pallidus together are the lentiform nucleus.
- Basal ganglia are gray matter inside CNS white matter, called nuclei but conventionally named ganglia.
Putamen Circuit
- The putamen circuit controls the execution of patterned motor activities (e.g., handwriting, cutting, hammering).
- Inputs: Premotor, supplementary, somatosensory, and some primary motor areas project to putamen.
- Pathway: Input → Putamen → Internal globus pallidus → Ventral anterior/lateral thalamic nuclei → Primary motor cortex and adjacent areas.
- Ancillary pathways involve external globus pallidus, subthalamus, and substantia nigra, which uses dopamine as a neurotransmitter.
Clinical Abnormalities Related to Putamen Circuit
- Chorea: Sudden, dance-like movements due to putamen lesions.
- Athetosis: Slow, snake-like hand movements due to globus pallidus lesions.
- Hemiballismus: Flailing movements of one side's limbs due to subthalamus lesions.
- Parkinson’s disease: Includes rigidity, akinesia, tremor, mainly from substantia nigra lesions.
Caudate Circuit
- The caudate circuit manages cognitive control over motor sequence patterns.
- Inputs mainly from association areas, plus premotor and supplementary areas.
- Pathway: Input → Caudate nucleus → Internal globus pallidus → Ventral anterior/lateral thalamic nuclei → Premotor and supplementary motor areas.
- Ancillary pathways connect caudate nucleus to putamen, then follow similar output; no involvement of subthalamus or substantia nigra.
Exam Practice Q&A (PG Entrance)
- Lesion of globus pallidus causes athetosis.
- Main basal ganglia role: planning and programming movement.
- Globus pallidus and putamen are part of the basal ganglia.
- Basal ganglia symptoms arise from ventral anterior thalamic nuclei.
- Caudate nucleus is not a cerebellar nucleus.
- Injury to corpus striatum leads to chorea.
- Dopamine is the main neurotransmitter in substantia nigra.
Key Terms & Definitions
- Basal Ganglia — Group of deep brain nuclei involved in motor control.
- Globus Pallidus — Basal ganglia component with internal/external parts.
- Putamen — Lateral part of the lentiform nucleus.
- Caudate Nucleus — C-shaped nucleus involved in motor and cognitive processes.
- Striatum — Combined caudate nucleus and putamen.
- Lentiform Nucleus — Globus pallidus plus putamen.
- Ancillary Pathways — Additional neural routes supporting main circuits.
- Substantia Nigra — Midbrain structure rich in dopamine neurons.
- Chorea/Athetosis/Hemiballismus — Movement disorders linked to specific basal ganglia lesions.
Action Items / Next Steps
- Review somatosensory cortex areas if uncertain about brain region functions.
- Study further details of Parkinson’s and Huntington’s disease as mentioned for future lectures.
- Practice answering previous PG entrance exam questions related to basal ganglia.