Figure 1.

The sensorimotor system incorporates all the afferent, efferent, and central integration and processing components involved in maintaining functional joint stability. Although visual and vestibular input contributes, the peripheral mechanoreceptors are the most important from a clinical orthopaedic perspective. The peripheral mechanoreceptors (pictured on the lower left) reside in the cutaneous, muscular, joint, and ligamentous tissues. Afferent pathways (dotted lines) convey input to the 3 levels of motor control and associated areas such as the cerebellum. Activation of motor neurons may occur in direct response to peripheral sensory input (reflexes) or from descending motor commands, both of which may be modulated or regulated by the associate areas (gray lines). Efferent pathways from each of the motor control levels (solid lines) converge upon the alpha and gamma motor neurons located in the ventral aspects of the spinal cord. The contractions by the extrafusal and intrafusal muscle fibers cause new stimuli to be presented to the peripheral mechanoreceptors.