Basal ganglia and movement control !
- Regulation
- Exam priority: high
Deep brain nuclei work as brake and accelerator for movement, letting the wanted action through. Dopamine keeps the balance.
Updated 2026-11-01
Also called: Direct and indirect pathways, Extrapyramidal system
See it in 3D: Caudate nucleus · Putamen · Globus pallidus · Substantia nigra · Thalamus
What it is
The basal ganglia (caudate, putamen, globus pallidus, subthalamic nucleus and substantia nigra) form loops from the cortex back to the cortex through the thalamus. Their output nuclei (internal globus pallidus and substantia nigra pars reticulata) keep the thalamus under constant inhibition. The direct pathway lifts this brake for the chosen movement; the indirect pathway tightens it to suppress competing ones. Dopamine from the substantia nigra pars compacta tips the balance toward movement, so its loss slows everything, while loss of striatal neurons in Huntington disease lets unwanted movements through.
Regulation
- +Direct pathway (D1 striatal neurons): Inhibits the output nuclei and frees the thalamus: facilitates the chosen movement
- −Indirect pathway (D2 striatal neurons, subthalamic nucleus): Increases output-nucleus inhibition of the thalamus: suppresses competing movements
- +Dopamine from substantia nigra pars compacta: Boosts the direct and damps the indirect pathway: net more movement
- −Striatal cholinergic interneurons: Oppose dopamine inside the striatum; relative excess adds to tremor and rigidity
- −Hyperdirect pathway (cortex → subthalamic nucleus): Fast, broad brake that stops an action already under way
Basal ganglia disorders
| Disorder | Lesion | Motor effect |
|---|---|---|
| Parkinson disease | Dopamine neurons of the substantia nigra pars compacta | Hypokinesia, rigidity, resting tremor |
| Huntington disease | Striatal neurons (caudate first), indirect pathway early | Chorea; later rigidity and dementia |
| Hemiballismus | Subthalamic nucleus, opposite side | Violent flinging of a limb |
| Drug-induced parkinsonism | D2 receptor blockade (antipsychotics) | Bradykinesia, rigidity |
| Wilson disease | Copper deposits in the putamen and lenticular nucleus | Tremor, dystonia, dysarthria |
Clinical notes
- Parkinson symptoms appear once roughly 60–80% of nigral dopamine neurons are lost, so the disease starts years before diagnosis.
- Parkinsonian resting tremor (pill-rolling) fades with voluntary movement, unlike the intention tremor of cerebellar disease.
- Levodopa crosses the blood–brain barrier on an amino acid carrier and is converted to dopamine; dopamine itself does not cross.
- MPTP, a contaminant of illicit opioid synthesis, destroys nigral neurons and reproduces parkinsonism.
Test yourself
Think of the answer, then tap the question to see it.
How can dopamine excite some striatal neurons and inhibit others yet always increase movement?
D1 receptors on direct-pathway neurons are excitatory (Gs); D2 receptors on indirect-pathway neurons are inhibitory (Gi). Boosting the first and damping the second both lower pallidal output and free the thalamus.
Why does a subthalamic nucleus lesion cause excess movement of the opposite limbs?
The subthalamic nucleus excites the internal pallidum. Without it pallidal output falls, the thalamus and motor cortex are released, and the cortex drives the opposite body: hemiballismus.
Huntington disease is a loss of neurons. Why does it begin with too much movement?
It first destroys indirect-pathway striatal neurons, removing the brake on unwanted movements (chorea). Later loss of direct-pathway neurons leads to rigidity and akinesia.
Why can antipsychotic drugs cause parkinsonism?
Many block D2 receptors in the striatum, mimicking dopamine loss on the indirect pathway, so movement becomes slow and rigid.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- The main neurotransmitters
- Motor cortex and the corticospinal tract
- Functions of the cerebellum
- The limbic system, emotion and reward
- Learning and memory
Related conditions
In Biochemistry
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 13.2 The Central Nervous System (OpenStax (Rice University), 2022); Parkinson Disease (StatPearls (NCBI Bookshelf), 2023); Neuroanatomy, Substantia Nigra (StatPearls (NCBI Bookshelf), 2023); Neuroanatomy, Globus Pallidus (StatPearls (NCBI Bookshelf), 2023); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 57). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.