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Structure

Basal ganglia

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This is the date the draft was written, not a medical review date.

The basal ganglia are a group of subcortical nuclei that modulate the initiation, scaling and selection of voluntary movement and contribute to habit and reward-related behaviour. They form loops with the cortex and the thalamus rather than acting as a primary motor pathway.

Terminologia Anatomica (Latin): Nuclei basales · Open in the 3D atlas

Location

Deep within the cerebral hemispheres, lateral to the thalamus and internal capsule; the substantia nigra lies in the midbrain and the subthalamic nucleus in the diencephalon.

Structure

The striatum (caudate nucleus and putamen), globus pallidus (external and internal segments), subthalamic nucleus and substantia nigra (pars compacta and pars reticulata). The putamen and globus pallidus together form the lentiform nucleus.

Blood supply

Mainly the lenticulostriate branches of the middle cerebral artery, the recurrent artery of Heubner (anterior cerebral artery) and the anterior choroidal artery; the midbrain nuclei are supplied from posterior circulation branches.

Innervation

As a central structure it has connections rather than peripheral nerves: cortical glutamatergic input to the striatum, nigrostriatal dopaminergic input, and output from the globus pallidus internus and substantia nigra reticulata to the ventral anterior and ventral lateral thalamus.

Function

Two overlapping pathways are usually described: the direct pathway facilitates desired movement, whereas the indirect pathway suppresses competing movement; dopamine from the substantia nigra pars compacta favours the direct pathway. This is a simplified model of a more complex circuit.

Clinical correlations

Parkinson disease follows loss of nigral dopaminergic neurons (bradykinesia, rigidity, rest tremor). Huntington disease involves striatal degeneration with chorea, and a lesion of the subthalamic nucleus classically causes contralateral hemiballismus. Management follows local guidelines.

Common exam points

  • Components: caudate, putamen, globus pallidus, subthalamic nucleus, substantia nigra.
  • Direct pathway facilitates, indirect pathway inhibits movement; dopamine favours the direct pathway.
  • Parkinson disease: nigral dopaminergic loss; resting tremor, rigidity, bradykinesia.
  • Huntington disease: caudate and putamen degeneration with chorea.
  • Subthalamic nucleus lesion: contralateral hemiballismus.

References

  1. Kandel ER, Koester JD, Mack SH, Siegelbaum SA. Principles of Neural Science. McGraw-Hill, 6th edition (2021) — Tier 3 (textbook)
  2. Haines DE, Mihailoff GA. Fundamental Neuroscience for Basic and Clinical Applications. Elsevier, 5th edition (2018) — Tier 3 (textbook)
  3. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)

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