<prompt> Pudendal nerve supplying motor pa to external sphincter is derived from :L5-S1 roots51-S2 rootsL2-L3 rootsS2-S3 rootsPHYSIOLOGY  <response>: S2-S3 roots There are two sphincters of the urethraa. Internal urethral sphincter also ka sphincter vesicae- it is involuntary in nature- made up of smooth muscle- supplied by sympathetic nerves, from lower thoracic upper lumbar segments of spinal cordb. External urethral sphincter also ka sphincter vesicae- it is voluntary in nature- made up of striated muscle fibres- supplied by the perineal branch of the pudendal nerve derived from spinal nerves S2,S3 S4 - it controls the membranous urethra and is responsible for the voluntary holding of urine. 