A method and system for selective inhibition of somatic nerve fibers in a mixed nerve containing both somatic and autonomic nerve fibers where the method finds use in treatment of chronic pain, spastic muscles and for sensory and motor control of a bladder. The methods and systems utilize alternate phase rectangular electrical pulses. An electrical pulse generator is coupled to a nerve. An alternate phase high frequency, low amplitude pulse is first applied to selectively inhibit somatic nerves when present in a mixed nerve. An alternate phase low frequency, high amplitude phase pulse subsequently supplied to stimulate the autonomic nerve fibers and in the case of the sacral root will permit a controlled voiding of the bladder and bowel.