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Understanding the Basal Ganglia: Anatomy, Functions, and Clinical Significance

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September 24, 2024

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Introduction

Scattered masses of gray matter in the subcortical substance of the cerebral hemisphere, the basal ganglia are responsible for:

• Learning motor functions
• Regulation of voluntary movements
• Control of muscular movements by influencing the cerebral cortex

Components of the Basal Ganglia

• Corpus striatum:
  • Neostriatum/striatum (caudate nucleus & putamen)
  • Paleostriatum/pallidum (globus pallidus)
• The putamen and globus pallidus form the lentiform nucleus
• Amygdaloid nucleus
• Claustrum
• Substantia nigra
• Subthalamic nucleus (of Luys)

Corpus Striatum

• Situated lateral to the thalamus
• Divided by the internal capsule into:
  • The caudate nucleus
  • The lentiform nucleus

Caudate Nucleus

• Largely C-shaped mass of gray matter
• Closely related to the lateral ventricle
• Relations:
  • Medially – thalamus
  • Laterally – internal capsule
• Parts:
  • Head
  • Body
  • Tail

Lentiform Nucleus

• Wedge-shaped mass of gray matter with a broad convex directed laterally and a blade directed medially
• Formed by the putamen laterally and globus pallidus medially
• Putamen and globus pallidus are separated by the external medullary lamina

Putamen

• Lateral part of the lentiform nucleus
• Continuous with the head of the caudate nucleus

Globus Pallidus

• Medial part of the lentiform nucleus
• Has 2 parts:
  • Medial part, globus pallidus internal
  • Lateral part, globus pallidus external
• Forms the projective zone

Claustrum

• A thin sheet of gray matter
• Separated from the lateral surface of the lentiform nucleus by the external capsule
• Lies medial to the insula

Substantia Nigra

• Located below the red nucleus
• Divided into 2 parts:
  • Pars compacta
  • Pars reticularis

Subthalamic Nucleus of Luys

• Lateral to the red nucleus
• Dorsal to substantia nigra

Connections of the Corpus Striatum and Globus Pallidus

• The corpus striatum (caudate nucleus and the putamen) forms the receptive/input zone of the basal ganglia.
• The globus pallidus forms the output zone of the basal ganglia.

Connections of the Corpus Striatum:

• Afferent fibers:
  • Corticostriate fibers
  • Thalamostriate fibers
  • Nigrostriate fibers
  • Brainstem striatal fibers
• Efferent fibers:
  • Striatopallidal fibers
  • Striatonigral fibers

Connections of the Globus Pallidus:

• Afferent fibers:
  • Striatopallidal fibers
• Efferent fibers:
  • Pallidofungal fibers divide into:
    • Ansa lenticularis to the thalamic nuclei
    • Fasciculus lenticularis to the subthalamus
    • Pallidotegmental to the tegmentum of the midbrain
    • Pallidosubthalamic fibers to the subthalamic nuclei

Functions Of The Basal Ganglia

• Regulation of voluntary movements
• Learning motor skills, e.g., throwing a basketball, using the wheel steering
• Control muscular movements by the cerebral cortex

Pathway Of Basal Ganglia

• The direct pathway is initiated by either excitatory cortical input and/or dopamine release from the substantia nigra.
• The indirect pathway is either activated by excitatory cortical input or inhibited dopamine release from the substantia nigra.

Vasculature

• Arterial supply:
  • Middle cerebral artery
  • Lenticostriate artery
  • Anterior cerebral artery
  • Anterior choroidal artery
  • Branches of posterior cerebral and posterior communicating arteries
• Venous drainage:
  • Striate branches of internal cerebral vein
  • Drain into the great cerebral vein

Clinical Correlates

• Hyperkinesia
• Hypokinesia
• Chorea
• Ballism
• Parkinson’s disease