Substantia nigra
The substantia nigra is one of the brainstem nuclei and part of the extrapyramidal system. They are situated in the anterior midbrain and mark the transition point of the tegmentum and cerebral peduncles.
While other nuclei such as the red nucleus as small and contained within an axial slice at the superior colliculi (see figure), the substantia nigra is seen in axial slices at both superior and inferior colliculi.
Function
It is an important relay station in the motor system. It consists of a compact part (dark, containing melonin) and a reticular part (reddish, containing iron). Most of its axons are projected diffusely to other brain areas and not arranged into tracts. Numerous axonal tracts terminate in the substantia nigra:
- caudate nucleus (striatonigral fibres)
- anterior cerebral cortex (corticonigral fibres)
- putamen
- precentral cortex
