17.24: Spinal Nerves: Plexus II
The plexuses of the lower body include the lumbar, sacral, and coccygeal plexuses, which innervate the abdomen, pelvis, legs, and coccygeal region. These plexuses control the transmission of sensory information and coordinate motor functions of the lower body.
The Lumbar Plexus
The lumbar plexus is situated within the lumbar region of the back and is primarily formed by the first four lumbar spinal nerves (L1 to L4). This plexus extends its branches into several nerves, including the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves. These nerves provide sensory and motor innervation to the muscles and skin of the abdomen, pelvis, and parts of the lower limbs. The lumbar plexus facilitates movements and transmits sensory information from these areas, enabling functions such as walking, posture maintenance, and the protection of abdominal organs.
The Sacral Plexus
Within the pelvis, the sacral plexus is formed by the nerves spanning from the fourth lumbar (L4) to the fourth sacral (S4) segments. This plexus gives rise to several vital nerves, including the pudendal, superior and inferior gluteal, posterior femoral cutaneous, and sciatic nerves. Notably, the sciatic nerve is recognized as the thickest and longest nerve in the body, extending down to the lower leg and foot. This nerve is a common source of pain and discomfort when irritated or compressed — a condition called sciatica. The sacral plexus primarily provides sensory and motor innervation to the pelvis and legs, overseeing functions such as leg movement, pelvic organ control, and sensation in the lower extremities.
Due to the substantial overlap in the nerves originating from the lumbar and sacral plexuses, these two networks are sometimes collectively referred to as the lumbosacral plexus. This combined structure highlights the complexity of neural pathways and their essential roles in bodily operations.
The Coccygeal Plexus
Though the smallest among the three, the coccygeal plexus plays a specific role in innervating the skin over the coccygeal area. It is located at the very base of the spine around the coccyx and primarily comprises the anococcygeal nerve. Despite its limited size and scope compared to the lumbar and sacral plexuses, the coccygeal plexus is crucial for transmitting sensory information from the coccygeal region, contributing to the overall sensory map of the lower body.
