Anterior Ramus of Second Lumbar Nerve

Origin

The anterior (ventral) ramus of the second lumbar nerve originates as one of two branches of the second lumbar nerve. The other branch is the posterior ramus of the same L2 nerve.

Course

The bifurcation of the second lumbar nerve into anterior and posterior rami takes place immediately after its exit from the intervertebral foramen. The anterior ramus of L2 contributes to the formation of the lumbar plexus, which also receives nerve fibers from the anterior rami of L1, L3, L4, and T12 (subcostal) nerves. The lumbar plexus is situated inside the substance of the psoas major muscle anterior to its attachment to the transverse processes of the lumbar vertebrae.

Branches

The anterior ramus of second lumbar 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 L2 segment of the spinal cord. These are lower motor neurons which exit the spinal cord through the anterolateral sulcus as they travel inside the anterior motor rootlets and root of L2 spinal segment. They subsequently travel through the second lumbar nerve to enter the anterior ramus before reaching the lumbar plexus. These efferent neurons travel through the branches of the genital branch of genitofemoral, femoral, and obturator nerve to supply motor innervation to various structures.

Somatic afferent neurons travel through the genital and femoral branches of genitofemoral nerve, lateral femoral cutaneous nerve of the thigh, cutaneous nerve branches of the obturator, and femoral nerve (medial, intermediate, and saphenous cutaneous nerves), to enter the lumbar plexus. From here onwards, these neurons travel through the anterior ramus of the second lumbar nerve to enter the sensory root and rootlets. The cell bodies of these sensory neurons are located inside the spinal ganglion of the second lumbar nerve. The axons then travel through the posterolateral sulcus to enter the posterior sensory horn of the L2 spinal cord segment.

The anterior ramus of second lumbar nerve is also connected to the sympathetic trunk through the white and gray communicating branches (rami communicantes). These serve as conduits for the preganglionic and postganglionic sympathetic neurons, respectively.

Supplied Structures & Function

The anterior ramus of second lumbar nerve supplies motor innervation to the cremaster muscle through the somatic efferent neurons running inside the genital branch of the genitofemoral nerve. They also provide motor innervation to the posterior abdominal wall musculature (psoas major and quadratus lumborum). In addition, these efferent neurons travel through the muscular branches of femoral nerve to innervate muscles of the anterior compartment of the thigh (iliacus, pectineus, sartorius, rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis muscles). Moreover, the efferent neurons from the anterior ramus of the second lumbar nerve travel through muscular branches of the obturator nerve to innervate muscles (adductor brevis, adductor longus, adductor magnus, gracilis, pectineus, and obturator externus muscles).

The somatic afferent neurons from the genitofemoral nerve conduct general sensory cutaneous information from the skin of the mons pubis, labium majus, and upper anterior part of the thigh. Those from the lateral femoral cutaneous nerve of thighs conduct sensory information from the anterior and lateral thigh to the level of the knee joint.

The general somatic afferent neurons from the medial, intermediate, and saphenous cutaneous branches of the femoral nerve transmit general sensations from the anterior and medial parts of thigh, and skin on the medial side of the leg, ankle, and foot. Some neurons exit from the obturator and femoral nerves to innervate the hip joint.