The substantia nigra is a crescent-shaped band of grey matter in the midbrain, just behind the cerebral peduncle. Its dorsal part looks black because its dopamine neurons contain neuromelanin. Functionally it belongs to the basal ganglia, and loss of its dopamine neurons is the core cause of Parkinson disease.
| Location | Midbrain, between the crus cerebri in front and the tegmentum behind, running the full length of the midbrain |
|---|---|
| Parts |
|
| Connections | |
| Blood Supply | Posterior cerebral artery perforators; Posterior communicating artery branches; Anterior choroidal artery; Superior cerebellar artery |
Supplies dopamine to the striatum to enable smooth, well-scaled voluntary movement, and acts as a basal ganglia output centre controlling eye movements and motor programmes.
Parkinson disease symptoms appear once roughly half or more of the nigral dopamine neurons are lost, producing slowness, rigidity, rest tremor and postural instability. Loss of normal nigral signal (the swallow tail sign) on high-resolution MRI and reduced dopamine transporter imaging support the diagnosis. Levodopa and dopamine agonists replace the missing dopamine.
Progressive degeneration of dopamine neurons in the pars compacta causing bradykinesia, rigidity, rest tremor and gait problems.
Parkinson-like symptoms caused by medicines that block dopamine receptors, such as antipsychotics and some anti-nausea drugs.
Severe, rapid parkinsonism from a toxin that selectively destroys nigral dopamine neurons, first described in people using contaminated synthetic opioids.
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