sacral spinal nerve 3 sacral spinal nerve 3 the sacral spinal nerve 3 (s3) is a spinal nerve of the sacral segment. sacral spinal nervethe plan of the lumbosacral plexusdetailsidentifierslatinnervi spinalisfma6425anatomical terminology it originates from the spinal column from below the 3rd body of the sacrum. sacrum, showing bodies in center. muscles s3 supplies many muscles, either directly or through nerves originating from s3. they are not innervated with s3 as single origin, but partly by s3 and partly by other spinal nerves. the muscles are: iliococcygeus puborectalis coccygeus sphincter urethrae membranaceae superior gemellus additional images sacral spinal nerve 3