A large mass of nerve fibers that originate in the motor control areas of the cerebral cortex in an area called the primary motor cortex and travel through the cerebral hemispheres (including the posterior internal capsule, which lies between the thalamus and globus pallidus), the brainstem (crossing at the bottom of the medulla), and the lateral part of the spinal cord before synapsing on the motor neurons that exit the spinal cord as nerve roots, eventually joining nerves to innervate individual muscles. It also is called the pyramidal tract or the corticospinal tract. The pyramidal pathway is so named because its course over the surface of the brainstem’s medulla resembles a pyramid in shape. Pyramidal nerves control gross voluntary and reflexive muscle function; the Extrapyramidal systEm refines this control to regulate fine motor movements. The extrapyramidal system often uses the same nerve structures to conduct its signals. The pyramidal pathway is not damaged in Parkinson’s disease, but the extrapyramidal system is, affecting the functions of both. A common representation of the relationship between the two is that of the relationship between musical instrument and musician. The pyramidal pathway is the instrument; the extrapyramidal system, the musician.