Pathophysiology of rigidity and akinesia in Parkinson's disease.

Although rigidity and akinesia are two of the cardinal features of Parkinson's disease, their exact pathophysiology remains uncertain. Mechanisms which may contribute to rigidity include accentuation of the long-latency component of the stretch reflex and enhanced fusimotor drive causing increased sensitivity of muscle spindles. Current evidence concerning the role of these factors in rigidity is reviewed. The relationship between akinesia, prolonged reaction times, and delay in initiation of internally generated movements in parkinsonian patients is discussed.