ABSTRACT
For Sherrington, the reflex was the elementary unit of behavior. A complex behavior was a compound of allied reflexes, reflexes that operated simultaneously or in sequence and served a common purpose. The starting point for Sherrington's analysis of the problem of coordination was the principle of the final common path. This principle refers to a simple but important fact: Different reflexes involve the same muscles. A flexion reflex excites the motor neurons to the flexor muscles and inhibits the motor neurons to the extensor muscles. An extension reflex uses the same motor neurons, but to different effect. The motor neurons are a keyboard upon which different reflexes play. Any process in the nervous system that is to be expressed in action must use much the same set of motor neurons as any other. What distinguishes one reflex from another is the spatial and temporal pattern of motor neuron activity, just as one piece of music is distinguished from another by the spatial and temporal pattern in which the piano keys are struck.
