Anterior Ramus of Fifth Sacral Nerve (Left)
Ramus anterior nervi sacralis quinti
Read moreQuick Facts
Origin: Fifth sacral nerve (S5).
Course: Exits from the sacral hiatus and ascends to penetrate the coccygeus muscle and enter the pelvic cavity, where it joins with the anterior ramus of S4 and coccygeal nerve to form the coccygeal plexus.
Branches: Anococcygeal nerves.
Supply: Motor innervation to the coccygeus muscle. Sensory innervation to the perianal skin in the anal triangle.
Origin
The anterior (ventral) ramus of fifth sacral nerve originates as one of two branches of the fifth sacral nerve, the other branch being the posterior ramus.
Course
The fifth sacral nerve bifurcates into anterior and posterior rami. Both rami exit from the sacral hiatus along with the cooccygeal nerve (Co). The anterior ramus of fifth sacral nerve, along with the anterior ramus of coccygeal nerve, penetrates the coccygeus muscle and join with a communicating branch from the anterior ramus of the fourth sacral nerve to form the coccygeal plexus. Anococcygeal nerves are given off from this coccygeal plexus.
Branches
The anterior ramus of fifth sacral nerve is a mixed nerve which contains both somatic efferent (motor) and afferent (sensory) neurons.
The somatic efferent neurons emerge from the anterior gray horn of the fifth sacral segment of the spinal cord. These are lower motor neurons that exit the cord through the anterolateral sulcus, as they travel inside the anterior motor rootlets and root of fifth sacral spinal segment. They subsequently travel through the fifth sacral nerve to enter the anterior ramus, prior to reaching the coccygeal plexus. They ascend to reach the anterior ramus of fourth sacral nerve and travel through the muscular branches of the fourth sacral anterior ramus to innervate the coccygeus muscle.
The dendrites of the somatic afferent neurons travel through the anococcygeal nerve (S4—Co) to enter the sacral plexus. These descend to reach the coccygeal plexus. From there onwards, these neurons travel through the sensory root and rootlets of the fifth sacral nerve. The cell bodies of these neurons are located inside the posterior root ganglion of the fifth sacral nerves. The axons then travel through the posterolateral sulci to enter the right posterior sensory horn of the fifth sacral cord segment.
The anterior ramus of fifth sacral nerve is also connected to the sympathetic trunk through the gray communicating branch (ramus communicans), which serves as a conduit for the postganglionic sympathetic neurons.
Supplied Structures & Function
The anterior ramus of fifth sacral nerve supplies motor innervation to the coccygeus muscle, through the general somatic efferent neurons, as they run inside the direct muscular branches of the anterior ramus of fourth sacral nerve. The general somatic afferent neurons conduct cutaneous general sensory information from the perianal skin via the anococcygeal nerve.
