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The pars compacta (SNpc) is one of two subdivisions of the substantia nigra of the midbrain (the other being the pars reticulata); it is situated medial to the pars reticulata. It is formed by dopaminergic neurons. [1] It projects to the striatum and portions of the cerebral cortex. [2] It is functionally involved in fine motor control.
The pars reticulata (SNpr) is a portion of the substantia nigra and is located lateral to the pars compacta. Most of the neurons that project out of the pars reticulata are inhibitory GABAergic neurons (i.e., these neurons release GABA , which is an inhibitory neurotransmitter ).
The differentiation between the substantia nigra pars reticulata and compacta was first proposed by Sano in 1910. [62] In 1963, Oleh Hornykiewicz concluded from his observation that "cell loss in the substantia nigra (of Parkinson's disease patients) could well be the cause of the dopamine deficit in the striatum." [63]
The substantia nigra is located in the ventral midbrain of each hemisphere. It has two distinct parts, the pars compacta (SNc) and the pars reticulata (SNr). The pars compacta contains dopaminergic neurons from the A9 cell group that forms the nigrostriatal pathway that, by supplying dopamine to the striatum, relays information to the basal ganglia.
Pars compacta; Pars reticulata; Interpeduncular nucleus; Cerebral peduncle. Crus cerebri; Mesencephalic cranial nerve nuclei. Oculomotor nucleus (III) Edinger-Westphal nucleus; Trochlear nucleus (IV) Mesencephalic duct (cerebral aqueduct, aqueduct of Sylvius)
The GPi, along with the substantia nigra pars reticulata, comprise the primary output of the basal ganglia, with its outgoing GABAergic neurons having an inhibitory function in the thalamus, the centromedian complex and the pedunculopontine complex.
The pedunculopontine nucleus lies below the red nucleus, caudal to the substantia nigra and adjacent to the superior cerebellar peduncle.It has two divisions of subnuclei; the pars compacta, containing mainly cholinergic neurons, and the pars dissipata, containing mainly glutamatergic neurons and some non-cholinergic neurons.
The same for the substantia nigra pars reticulata. [11] The subthalamic nucleus sends axons to another regulator: the pedunculo-pontine complex (id). The lateropallido-subthalamic system is thought to play a key role in the generation of the patterns of activity seen in Parkinson's disease. [20]