Onuf's nucleus is a distinct group of neurons located in the ventral part (laminae IX) of the anterior horn of the sacral region of the human spinal cord involved in the maintenance of micturition and defecatory continence, as well as muscular contraction during orgasm. It contains motor neurons, and is the origin of the pudendal nerve. The sacral region of the spinal cord is fourth segment (cervical, thoracic, and lumbar being the first three) of vertebrae in the spinal cord which consists of the vertebrae 26-30.