Sacral Plexus

INTRODUCTION:
  • Lies immediately inferior to the lumbar plexus. 
  • Formed by the anterior rami of spinal nerves L4, L5, and Si through S4. 
  • Contain fibers from the nerves of the lumbar plexus through the lumbosacral trunk; hence the two plexuses are described collectively as the lumbosacralplexus. 
STRUCTURE:
  • Sacral plexus is formed by: 
  1. Lumbosacral trunk 
  2. Anterior division of the first sacral nerve 
  3. Portions of the anterior divisions of the second and third sacral nerves 
  • The nerves forming the sacral plexus converge toward the lower part of the greater sciatic foramen, and unite to form a flattened band, from the anterior and posterior surfaces of which several branches arise. 
  • The band itself is continued as the sciatic nerve, which splits on the back of the thigh into the tibial nerve and common fibular nerve; these two nerves sometimes arise separately from the plexus, and in all cases their independence can be shown by dissection. 
  • Often, the sacral plexus and the lumbar plexus are considered to be one large nerve plexus, the lumbosacral plexus. 
  • The lumbosacral trunk connects the two plexuses. 
  • Sacral plexus, Nervi erigentes (S2,3,4) & pudenal nerve are involved in process of erection of penis 
RELATIONS:
  • The sacral plexus lies on the back of the pelvis between the piriformis muscle and the pelvic fascia. 
  • In front of it are the internal iliac artery, internal iliac vein, the ureter, and the sigmoid colon. 
  • The superior gluteal artery and vein run between the lumbosacral trunk and the first sacral nerve, and the inferior gluteal artery and vein between the second and third sacral nerves. 
  • Structures passing through Greater sciatic foramen: 
  1. Above pyriformis — superior gluteal nerves and vessels 
  2. Below pyriformis- pudenal nerve leaves pelvis to enter gluteal region 
  • Structures passing through lesser sciatic foramen: 
  1. Pudendal nerve( leaves gluteal region to enter pudenal canal) lies in relation to Ischial spine 
  2. Internal pudendal vessels 
  3. Nerve to obturator internus 
  4. Tendon of obturator internus 
OTHER BRANCHES OF THE SACRAL PLEXUS

Nerve SpinalComponents Innervation
Superior gluteal L4, L5, S1 Abductor muscles of thigh (gluteus minimus, gluteus medius, tensor fasciae latae)
Inferior gluteal L5-52 Extensor muscle of hip joint (gluteus maximus)
Nerve to piriformis S1, 52 Abductor and rotator of thigh (piriformis)
Nerve to quadratuslemon's L4, L5, S1 Rotators of thigh (gemellus inferior, quadratus femoris)
Nerve to internalobturator L5-S2 Rotators of thigh (gemellus superior, internal obturator)
Perforating cutaneous S2, S3 Skin over lower medial surface of buttock
Posterior cutaneousfemoral S1 -S3 Skin over lower lateral surface of buttock, anal region, upper posterior surface of thigh, upper aspect of calf, scrotum in male and labia majora in female
Sciatic L4-S3 Composed of two nerves (tibial and common fibular); splits into two portions at popliteal fossa; "hamstring muscles" (biceps femoris, semitendinosus, semimembranosus) and adductor magnus muscle
Sacral muscular S4 Levator ani, External anal sphincter
Sacral visceral S2-S4 Pelvic splanchnic nerve
Pudendal( sensory & motor) S2-S4 Skin of penis and scrotum in male and skin of clitoris, labia majora, labia minora, and lower vagina in female; muscles of perineum, anal canal
Exam Question
  • Nerves passing through lesser sciatic foramen are obturator internus & pudenal nerve 
  • Superior gluteal nerve supplies Gluteus medius, Gluteus minimus & Tensor fasia lata 
  • Pudendal nerve supplying motor part to external sphincter is derived from S2-S4 roots 
  • Gluteus medius is supplied by superior gluteal nerve 
  • Pudenal nerve is both sensory and motor 
  • Sacral plexus, Nervi erigentes (S2,3,4) & pudenal nerve are involved in process of erection of penis 
  • Pudendal nerve leaves pelvis and enters gluteal region through greater sciatic foramen 
  • Pudendal nerve leaves the gluteal region by passing through the lesser sciatic foramen and enters the pudendal canal 
  • Anal canal Supplied by pudendal nerve 
  • Ischial spine is related to pudenal nerve
Don't Forget to Solve all the previous Year Question asked on Sacral Plexus