The nerves of the lower limb are formed by a few important plexuses. The lumbar plexus and the sacral plexus are the two main plexuses of the lower limb that are responsible for providing sensory and motor innervation to the muscles and structures in the lower limb.
The lumbar plexus is formed by the anterior rami of spinal nerves L1-L4 and lies within the posterior abdominal wall. The lumbar plexus has three terminal branches, namely, the femoral nerve, obturator nerve, and lateral cutaneous nerve of the thigh. Each of these nerves has important functions in providing sensory and motor innervation to the muscles and structures of the lower limb.
The femoral nerve descends through the psoas major muscle and gives off four branches that provide sensory and motor innervation to the anterior thigh. The obturator nerve passes through the obturator foramen to provide sensory and motor innervation to the medial thigh and hip joint. The lateral cutaneous nerve of the thigh emerges from the lateral border of the psoas major and provides sensory innervation to the skin of the anterolateral thigh.
The sacral plexus is formed by the anterior rami of spinal nerves L4-S4 and lies between the piriformis and the coccygeus muscles. The sacral plexus gives rise to the sciatic nerve, which is the largest nerve in the body and provides motor and sensory innervation to the entire lower limb. The sciatic nerve is composed of two main nerve branches: the tibial nerve and the common fibular (peroneal) nerve.
The tibial nerve descends through the popliteal fossa and enters the posterior compartment of the leg to innervate the muscles and structures on the posterior aspect of the leg. This nerve branch is responsible for providing motor and sensory innervation to the rear of the leg.
The common fibular (peroneal) nerve descends to provide sensory and motor innervation to the lateral and anterior compartments of the leg. This nerve branch divides into two branches, the superficial fibular (peroneal) nerve and the deep fibular (peroneal) nerve, in the fibular neck region. The superficial fibular (peroneal) nerve supplies the muscles and skin on the lateral aspect of the leg and dorsum of the foot, while the deep fibular (peroneal) nerve provides motor innervation to the muscles in the anterior compartment of the leg and dorsal extensor muscles of the foot.
The lumbar plexus and the sacral plexus are primarily responsible for the sensory and motor innervation of the lower limb. Together, these two plexuses provide the neurological input necessary for the functioning of the lower limb muscles and structures.
