Substantia nigra

Location and borders

• Brainstem localization — located in the midbrain (Mesencephalon), which lies rostral to the pons.
• Topography on section — lies between the tegmentum (tegmentum) and the crus cerebri (crus cerebri).
• Adjacent structures — posteriorly, the structure borders the rostral part (the so-called red zone) of the globus pallidus (globus pallidus).

Structure and biochemical features

• Anatomical division — subdivided into the pars compacta and pars reticulata.
• Cellular composition — contains dopaminergic neurons.
• Biochemistry — characterized by a high iron content; a high level of iron is also characteristic of the globus pallidus and the red nucleus. The dark, saturated color of the substantia nigra is due to a high content of melanin.
• System affiliation — belongs to the midbrain nuclei associated with the basal ganglia.

Functions and pathways

• Connections with the striatum — maintains reciprocal relationships with the striatum (corpus striatum).
• Connections with the cortex — connected to the cerebral cortex via projection fibers passing through the internal capsule (capsula interna).
• Motor function — participates in the regulation of fine movements, such as finger movements.
• Regulation of complex acts — participates in chewing, swallowing, and their sequencing.
• Higher nervous activity — participates in the organization of emotional behavior.

Clinical significance and pathologies

• Parkinson's disease — a degenerative disease primarily affecting the substantia nigra. The pathological process involves the selective and progressive destruction of pigmented dopaminergic neurons. Degeneration begins in the presynaptic axon terminals; one hypothesis is a disruption of retrograde axonal transport of neurotrophic factors. Histological findings include a decrease in neuron count, gliosis, and Lewy bodies. Clinically, the disease manifests as resting tremor, muscle rigidity, hypokinesia, and postural instability.
• Weber's syndrome — an alternating brainstem syndrome involving the crus cerebri. A frequent cause is occlusion of the interpeduncular branches of the posterior cerebral and posterior choroidal arteries; the syndrome may also occur in generalized arterial hypertension. Involvement of the substantia nigra is accompanied by contralateral parkinsonism and rigidity, combined with ipsilateral oculomotor nerve palsy.
• Wilson's disease — a disorder of copper metabolism. On T2-weighted MRI, a high-intensity signal is noted from the midbrain gray matter due to parenchymal brain tissue damage caused by elevated blood copper concentrations.
• Vascular parkinsonism — a reliable diagnosis requires mandatory MRI verification of changes in the substantia nigra, putamen, and thalamus.
• Psychopharmacology — atypical antipsychotics are used in the treatment of psychoses. Blockade of 5-HT₂A receptors reciprocally increases dopamine activity in the nigrostriatal system, reducing the risk of extrapyramidal symptoms.

Class and exam questions

What else to study on this topic

• Extrapyramidal system and basal ganglia
• Red nucleus (Nucleus ruber)
• Weber's syndrome (alternating syndrome)
• Parkinson's disease and Lewy bodies

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.