CorpusHuman Anatomy
NervousBrain region

Basal nuclei

Nuclei basales

Also known as: basal ganglia, corpus striatum, striatum, lentiform nucleus

Deep grey-matter nuclei of the cerebrum (caudate, putamen, globus pallidus), functionally linked with the subthalamic nucleus and substantia nigra, that select and scale movements, form habits and modulate cognition and motivation through cortico-basal-thalamo-cortical loops.

Show on body map

Overview

Anatomically the basal nuclei are the caudate nucleus, the putamen and the globus pallidus.
• Caudate + putamen = striatum, the input nucleus, named for the grey bridges striping the internal capsule between them.
• Putamen + globus pallidus = lentiform nucleus, so named for its shape.
• The nucleus accumbens (ventral striatum) joins the caudate head and putamen.
• Functionally the system also includes the subthalamic nucleus (diencephalon) and the substantia nigra (midbrain).
The caudate is C-shaped, with a head, body and tail following the curve of the lateral ventricle and forming its lateral wall. The lentiform nucleus lies lateral to the internal capsule.

The circuitry is a set of parallel loops: cortex → striatum → GPi/SNr → thalamus (VA/VL) → cortex. The output nuclei (GPi, SNr) are GABAergic and tonically inhibit the thalamus. Two pathways run between the striatum and the output:
• Direct pathway (striatal neurons with D1 receptors, containing substance P): striatum inhibits GPi → thalamus is disinhibited → movement is facilitated ("go").
• Indirect pathway (D2 neurons, containing enkephalin): striatum inhibits GPe → STN is disinhibited → glutamatergic STN excites GPi → thalamus is more inhibited → competing movements are suppressed ("no-go").
• Dopamine from the substantia nigra pars compacta excites the direct pathway (D1) and inhibits the indirect pathway (D2), so either way it favours movement.
Parallel loops handle eye movement (caudate), cognition (dorsolateral prefrontal) and emotion and motivation (accumbens, orbitofrontal).

Basal-nuclei disorders produce either hypokinetic syndromes (Parkinson) or hyperkinetic syndromes (chorea, ballism, dystonia, tics), always contralateral to the lesion and without weakness.

Location

Deep in each cerebral hemisphere: caudate in the lateral wall of the lateral ventricle; lentiform nucleus lateral to the internal capsule, medial to the external capsule, claustrum and insula.

Parts & subdivisions

  1. Caudate nucleus
    Head (bulging into the frontal horn), body and tail (in the roof of the temporal horn). Cognitive and oculomotor loops; atrophies early in Huntington disease (boxcar ventricles).
  2. Putamen
    Lateral part of the lentiform nucleus; main motor input zone; commonest site of hypertensive haemorrhage.
  3. Globus pallidus
    External (GPe; indirect pathway) and internal (GPi; main output) segments; GABAergic.
  4. Nucleus accumbens (ventral striatum)
    Limbic loop: reward, motivation and addiction; receives mesolimbic dopamine from the VTA.
  5. Subthalamic nucleus
    Glutamatergic nucleus of the indirect pathway; a lesion causes contralateral hemiballismus; target of deep brain stimulation for Parkinson disease.
  6. Substantia nigra
    Pars compacta (dopamine to the striatum) and pars reticulata (output, like GPi).

Anatomy

Arterial supply

Lenticulostriate branches of the MCA (most of the putamen, globus pallidus, body of caudate); recurrent artery of Heubner (head of caudate, anterior putamen); anterior choroidal artery (medial globus pallidus).

Function

  • Selection and initiation of desired movements and suppression of unwanted ones
  • Scaling of movement amplitude and velocity
  • Procedural learning and habit formation
  • Control of saccadic eye movements
  • Cognitive flexibility, motivation and reward-based learning

Clinical significance

Huntington disease

An autosomal-dominant CAG trinucleotide repeat expansion in HTT (chromosome 4) shows anticipation through paternal transmission. It causes loss of the striatal GABAergic neurons of the indirect pathway, so movement is disinhibited, producing chorea. Psychiatric change and subcortical dementia accompany it, onset is typically at 30–50 years, and MRI shows caudate atrophy.

Hemiballismus

Violent, flinging, large-amplitude movements of the contralateral limbs, classically from a lacunar infarct of the contralateral subthalamic nucleus.

Parkinsonism and Wilson disease

Parkinson disease results from loss of nigrostriatal dopamine. Wilson disease (ATP7B, copper accumulation) damages the putamen ("hepatolenticular degeneration"), causing tremor, dystonia and psychiatric features, with Kayser–Fleischer rings.

Mnemonics

Direct vs indirect

"D1 = Direct = Do (go); D2 = inDirect = Don't." Dopamine excites D1 and inhibits D2, so it says GO through both.

Lentiform vs striatum

"Lentiform = Putamen + Globus pallidus (the lens is PG-rated); Striatum = Caudate + Putamen."

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.