pars compacta

Structure

• the pars compacta of the substantia nigra is a dorsal stratum of 450,000 closely spaced pigmented, melanin-containing dopaminergic neurons.
• these darkly pigmented dopaminergic neurons contain 80% of dopamine in the central nervous system.

Afferents

• the nigrostriatal system is reciprocated by a massive striatonigral fiber system with multiple neuro-transmitters, but chiefly GABA
• the substantia nigra receives smaller afferent projections from the subthalamic nucleus, the lateral segment of the globus pallidus, the dorsal nucleus of the raphe, & the pedunculopontine nucleus of the midbrain.

Efferents

• the dopaminergic neurons project inhibitory fibers to the striatum (caudate & putamen)
• other non dopaminergic neurons project to the rostral part of the ventral nucleus of the thalamus

Pathology

• the pars compacta appears depigmented with loss of neurons in brains from victims of Parkinson's disease

More general terms

• CNS nucleus

Component of

• substantia nigra (nucleus niger, Soemmerring's ganglion)