in the case where sensory nerves are stimulated, the reflex arcs are triggered by the stimulation on sensory nerve axons at specific peripheral sites. one example of such a reflex is the flexor withdrawal reflex. the flexor withdrawal reflex occurs naturally when a sudden, painful sensation is applied to the sole of the foot. it results in flexion of the hip, knee and ankle of the affected leg, and extension of the contralateral leg in order to get the foot away from the painful stimulus as quickly as possible. the sensory nerve stimulation can be used to generate desired motor tasks, such as evoking flexor withdrawal reflex to facilitate walking in individuals following stroke, or they can be used to alter reflexes or the function of the central nervous system. in the later case, the electrical stimulation is commonly described by the term "neuromodulation".