Basal Ganglia

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Basal ganglia and basal ganglia neurotransmitters

Connections of the basal ganglia

  1. cortical motor commands occur in correlation with cortical activation of the basal ganglia which project to the thalamus, which in turn sends projections back to the cortex in the premotor and motor cortices probably to the same area where the impulse originated from. The system is complementary and contemporaneous to cerebellar activity; thus voluntary movement is initiated in the cerebral cortex, organized by the basal ganglia prior to thalamic integration with cerebellar coordination added before final return to the motor areas of the cortex
    1. sensorimotor cortex projects to the putamen
    2. association cortex of frontal, parietal, and limbic system project to the caudate
  2. initial stage of processing occurs in the caudate and putamen, information passes through the globus pallidus for output to the thalamus; substantia nigra and subthalamic nucleus provide control of the caudate and putamen (substantia nigra), and globus pallidus (subthalamic nucleus)
    1. NOTE: substantia nigra pars compacta sends dopaminergic axons to the neostriatum while the ventral tegmental area anterior to it sends dopaminergic axons to the hypothalamus, limbic system, and cerebral cortex
    2. NOTE: caudate nucleus provides a boundary to the lateral ventricle, frontal horn, trigone and temporal horn
  3. a decrease in basal ganglia inhibitory discharge to the thalamus allows the thalamus to increase its excitation (glutamate) of cortically initiated movements while an increase in basal ganglia inhibitory discharge has the opposite effect
    1. the overall circuit provides 1) excitatory input (glutamate) from the cerebral cortex to the caudate and putamen; 2) the caudate and putamen inhibit (GABA) the globus pallidus; 3) the globus pallidus inhibits (GABA) the thalamus; 4) the thalamus has excitatory effects (glutamate) inhibited to various degrees by the basal ganglia
  4. Caudate and putamen connections
    1. Input is ipsilateral from the cerebral cortex, thalamus (from centromedian (CM) nucleus) and substantia nigra; cortical and thalamic input is excitatory (glutamate) while substantia nigra input is dopaminergic and is excitatory to some cells (D1 receptors-substance P spiny cells) and inhibitory to others (D2 cells-enkephalin spiny cells)
    2. Output is inhibitory to globus pallidus (main) and substantia nigra
  5. Globus pallidus connections to thalamus include centromedian (CM), ventral anterior (VA), and ventrolateral (VL)
  6. Remember: cortex, thalamus, subthalamic nuclei, and part of the substantia nigra outputs are excitatory; putamen, caudate, globus pallidus, and part of the substantia nigra outputs are inhibitory
  7. Basal ganglia disease
    1. Degree of inhibition of the basal ganglia to the thalamus is responsible for the nature of the disorders; greater pallidothalamic inhibition results in hypokinesia (greater output to the thalamus), less inhibition yields hyperkinesias; signs occur contralateral to the affected basal ganglia because descending paths are crossed corticospinal tracts
    2. Parkinson’s disease (hypokinesia, tremor, rigidity) is caused by loss of 75% or more of dopaminergic neurons of the substantia nigra; the combined excitatory and inhibitory effects of dopamine on the caudate and putamen account for the mixed hypokinesia, hyperkinesias (tremor) that is seen in the disease; overall pallidal activity in Parkinson’s disease is increased
    3. NOTE: also see degeneration of the raphe nucleus, locus ceruleus and dorsal motor nucleus of the vagus
    4. Hemiballism – flailing or swinging movements resulting from lesions of the contralateral subthalamic nucleus
    5. Chorea – (dance-like movements) – thought to be due to lesion in the caudate or putamen
    6. Dystonia – (prolonged contractions or transient or sustained distortions of posture of limbs or trunk) – lesion site uncertain
    7. Blood supply of basal ganglia/thalamus and resulting lesions
    • Head of caudate supplied by recurrent artery of Heubner, usually a branch of A2
    • Putamen and anterior limb of internal capsule (posterior portion) mostly supplied by lenticulostriate branches of MCA
    • Globus pallidus supplied by anterior choroidal artery; this is why treatment for Parkinson’s disease used to include surgical ligation of the anterior choroidal
    • Anterior and posterior limbs of the internal capsule are supplied by the lenticulostriate branches of the MCA; the recurrent artery of Heubner supplies the rostromedial parts of the anterior limb; direct branches from the ICA supply the genu while the retrolenticular and ventral portions of the posterior limb are supplied by the anterior choroidal artery
        • occlusion of Heubner causes hemiparesis (predominantly in the arm and face) and expressive aphasia if occluded on the dominant side
    • Posterior limb of internal capsule supplied by both lenticulostriate branches of MCA and ventral part of the anterior choroidal artery (occlusion may cause contralateral hemiplegia, hypesthesia, and homonymous hemianopsia (supplies optic radiations))
        • blood supply of the internal capsule include the MCA, ICA, anterior choroidal, Pcomm, and ACA (NOTE: Not the PCA)
    • Medial thalamus – supplied by medial ganglionic branches of the circle of willis, medial posterior choroidal, anterior choroidal, and basilar artery branches
    • Lateral thalamus - supplied by thalamogeniculate branches of PCA
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