Nerve to coccygeus muscle

The nerve to coccygeus muscle innervates the coccygeus muscle, which forms the posterior part of the pelvic floor. The coccygeus helps to support the pelvic viscera–along with the levator ani–and pulls the coccyx forwards after defecation. A lesion to the nerve could lead to weakening of the posterior pelvic floor.

The nerve to coccygeus muscle comprises of neuronal fibers arising from the anterior rami of the fourth and fifth sacral spinal nerves (S4 and S5), which could reach out to the coccygeus muscle directly from the sacral plexus or indirectly via the coccygeal plexus. To understand the later, one has to know that the coccygeal plexus is formed underneath the pelvic floor mainly from the anterior rami of the fifth sacral (S5) and coccygeal (Co) spinal nerves. The plexus gives off neuronal offshoots that penetrate the coccygeus muscle from underneath to ascend in the pelvic cavity, where they join with the anterior ramus of S4 spinal nerve to form a single neuronal trunk. This trunk gives off anococcygeal nerves that penetrate and innervate the coccygeus muscle, apart from providing cutaneous innervation to the peri-anal skin.