Final answer:
The sciatic nerve, correctly defined by Option 3, is a major peripheral nerve running from the sacral plexus to just above the knee, and it is involved in controlling voluntary muscle movements in the lower limb.
Step-by-step explanation:
The sciatic nerve option that correctly defines it is Option 3: Major peripheral nerve of the hind limb coursing caudal to the femur. This nerve is a systemic nerve arising from the sacral plexus and is formed by a combination of the tibial and fibular nerves. The sciatic nerve is the longest and thickest in the body, running from the lower region of the spinal cord to just above the knee. It extends across the hip joint and gluteal region into the upper posterior leg, and when inflamed or compressed, it can lead to a painful condition known as sciatica.
The somatic nervous system (SNS) controls mainly voluntary muscle movements, and the sciatic nerve as part of this system, plays a significant role in the mobility of the lower limb by innervating muscles and skin of the posterior thigh, part of the lower leg, and the foot.