Sciatic Nerve

INTRODUCTION:
  • Thickest nerve in the body & Largest branch of sacral plexus.
  • Sciatic nerve ( also called ischiadic nerve, ischiatic nerve) is a large nerve in humans and other animals.
  • It begins in the lower back and runs through the buttock and down the lower limb.
  • It is the longest and widest single nerve in the human body, going from the top of the leg to the foot on the posterior aspect.
  • The sciatic nerve provides the connection to the nervous system for nearly the whole of the skin of the leg, the muscles of the back of the thigh, and those of the leg and foot.
  • It is derived from spinal nerves L4 to S3.
  • It contains fibers from both the anterior and posterior divisions of the lumbosacral plexus.
BRANCHES:
  1. Tibial Nerve
  2. Common Peroneal Nerve.
COURSE:
  • In pelvis: lies in front of piriformis.
  • Sciatic nerve leaves the pelvis and runs posteriorly in the thigh.
  • In the upper angle of popliteal fossa, sciatic nerve divides into tibial nerve and common peroneal nerve
  • In gluteal region: the nerve enters the gluteal region through greater sciatic foramen below the piriformis.
RELATIONS:
  • Relations in gluteal region:
  1. Superficial or posterior: gluteus maximus
  2. Deep or anterior: body of the ischium, tendon of obturator internus with gemelli, Quadratus femoris, obturator externus , capsule of hip joint & upper transverse fibres of adductor magnus.
  3. Medial: inferior gluteal nerve and vessels
  4. In the thigh: the nerve enters the back of the thigh at the lower border of the gluteus maximus.
  • Relations in thigh region:
  1. Superficial or posterior: nerve is crossed by long head of biceps femoris.
  2. Deep or anterior: nerve lies on the & supplies adductor magnus.
  3. Medial: semi membranosus Ex semitendinosus
  4. Lateral: biceps femoris.
  • The sciatic nerve in the buttock lies deep to the gluteus maximus muscle, midway between the greater rochanter and the ischial tuberosity.
CLINICAL SIGNIFICANCE:
  • A posterior dislocation of the hip joint will generally injure the sciatic nerve.
  • A herniated disc or pressure from the uterus during pregnancy may damage the nerve roots, resulting in a condition called sciatica (sharp pain in the gluteal region that extends down the post. side of the thigh.)
  • An improperly administered injection into the buttock may injure the sciatic nerve.
Exam Question
  • Sciatic nerve is the thickest nerve of body
  • Nerve supply of adductor magnus is through sciatic & obturator nerve
  • Sciatic nerve leaves pelvis & runs posteriorly in the thighs
  • Sciatic nerve enters the gluteal region through greater sciatic foramen
  • A posterior dislocation of the hip joint will generally injure the sciatic nerve
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