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Substantia Nigra

Substantia NigraLatin for 'black substance'

The substantia nigra is a brain structure located in the midbrain, and forms part of the basal ganglia. It is the largest nucleus in the midbrain. The function of the basal ganglia is to control voluntary movement, to produce the neurotransmitter dopamine, and to regulate mood. The substantia nigra also plays an important role in reward and addiction. Essentially there are two compartments within the substantia nigra: pars compacta  and pars reticulata, both of which have very different functions and connections. 

Pars compacta - Ingoing
This part of the brain mainly provides input to the basal ganglia circuit, in particular supplying the striatum with dopamine. Due to it's large involvement within motor control, death of dopamine can result in a disease called Parkinson's disease 

Pars Reticulata - Outgoing
This part of the brain mainly works as an output, conveying signals from the basal ganglia to the other brain structures. The neurons of the pars reticulata produce the neurotransmitter GABA (gamma-aminobutyric acid).