Motor Tracts, Basal Ganglia, and Dopamine Pathways
Several
major neuronal tracts coordinate somatic motor functions. One is the pyramidal
tract, whose direct motor component goes from the precentral gyrus through the
internal capsule and midbrain and terminates on motor neurons in the anterior
horn of the spinal cord. Extrapyramidal tracts (eg,
rubrospinal, reticulospinal, and corticoreticular) are also important for motor
control. The basal ganglia (including caudate nucleus, putamen, and globus
pallidus) are subcortical masses found between the cerebral
cortex and thalamus that, together with the substantia nigra,
help to coordinate movement. A major pathway, the nigrostriatal, originates in
the substantia nigra and connects with basal ganglia and other structures. The substantia
nigra receives reciprocal input from these structures
plus others. Efferent pathways (nigrostriatal) are dopaminergic; afferent input
is from neurons containing 5HT, GABA, and substance P. Defects in these pathways
lead to motor incoordination or incapacity.
