Location: Mesencephalon (midbrain), ventral tegmentum. Named for its dark colour — SNc neurons accumulate neuromelanin as a by-product of dopamine synthesis. Depigmentation visible at autopsy in Parkinson’s disease.
Full explanation with circuits, clinical detail, and tables: Substantia Nigra – Anatomy, Subdivisions & Function
Two subdivisions
| Division | Neurotransmitter | Key Function |
|---|---|---|
| SNc (pars compacta) | Dopamine | Nigrostriatal projection → dorsal striatum (D1 + D2 MSNs) → motor action selection |
| SNr (pars reticulata) | GABA | BG output nucleus; tonically suppresses superior colliculus → gates saccades (functionally equivalent to GPi) |
SNc vs VTA — same transmitter, different target
| SNc | VTA | |
|---|---|---|
| Pathway | Nigrostriatal | Mesolimbic |
| Target | Caudate + Putamen | Nucleus accumbens, PFC |
| Function | Motor selection | Reward, motivation |
| Disease | Parkinson’s | Depression, addiction |
→ See ventral tegmentum for the mesolimbic side.
Dopamine effect on striatum
- DA → D1 MSNs: excitatory → direct pathway → movement facilitated
- DA → D2 MSNs: inhibitory → indirect pathway suppressed → competing movements blocked
- Both = “go” signal. Loss of DA → D1 falls + D2 disinhibited → GPi overactive → thalamus clamped → bradykinesia
Symptoms only emerge when >60–70% of SNc neurons are lost (large reserve capacity).
Clinical
- Parkinson’s disease — selective SNc degeneration; Lewy bodies (alpha-synuclein) in surviving neurons
- MPTP model — MPTP → MPP+ (via MAO-B) → destroys SNc via DAT uptake + Complex I inhibition; spares VTA
see also
ventral tegmentum
Parkinson’s disease
basal ganglia
Tags: neuroscience science gehirnregion
Superlink: 050 🧠Neuroscience
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Created: 30-05-24 18:06