The word ’sciatica’ derives from the term sciatic nerve. Sciatic pain is a very specific kind of referred pain, one that is experienced at one or more places along the course of the sciatic nerve, which is the major nerve of the leg (and, incidentally, the nerve with the largest diameter in the human body). The sciatic nerve – one for each leg, of course – starts at the lower end of the spine and continues down behind the thigh. Directly above the knee joint, the sciatic nerve divides into two main branches – the tibial and common peroneal nerves – one branch travelling down the shin to the big toe, and the other running down the back of the calf to the heel before it winds around to the front of the foot and then extends into the toes.
The above is, of course, but a simplified description of the sciatic nerves; if you were to look in Gray’s Anatomy, the classic volume that still remains a standard medical reference nearly 150 years after it was first published, you’d find that more than four pages of small type are devoted to listing all the intricate sub-divisions of these nerves. While little purpose would be served by going into all this detail, it is important to note that almost any part of the leg can be affected by sciatic pain.