Nerves of the Pelvis

Question 1

What forms the sacral plexus?

Answer 1

1. lumbosacral trunk (L4, L5): part of the lumbar plexus

2. anterior primary rami of S1-S4

Question 2

Where does the sacral plexus lie?

Answer 2

primarily on the anterior surface of piriformis

Question 3

Where do the anterior primary rami of S1-S4 enter the pelvis?

Answer 3

through the anterior sacral foramina

Question 4

What are the branches of the sacral plexus that supply the buttock and lower limb?

Answer 4

1. superior gluteal nerve (L4-S1)
2. inferior gluteal nerve (L5-S2)
3. sciatic nerve (L4-S3)
4. nerve to obturator internus muscle (L5-S2)
5. nerve to quadratus femoris muscle (L5-S1)
6. posterior cutaneous nerve of the thigh (S1-S3)

Question 5

Describe the superior gluteal nerve.

Answer 5

• from L4-S1
• exits the pelvis through the greater sciatic foramen superior to piriformis
• supplies the gluteus medius, gluteus minimus, and tensor fasciae latae muscles
• impingement or injury results in trendelenberg’s gait
• anterior gluteal muscles prevent pelvis from slumping to unsupported side during gait

Question 6

Describe the inferior gluteal nerve.

Answer 6

• from L5-S2
• exits the pelvis through the greater sciatic foramen inferior to piriformis
• supplies the gluteus maximus
• gluteus maximus functions in trunk control and standing from a seated position

Question 7

Describe the sciatic nerve.

Answer 7

• from L4-S3
• the largest nerve in the body
• exits the pelvis through the greater sciatic foramen inferior to piriformis
• supplies numerous structures in the lower extremity
• impingement causes sciatica

Question 8

Describe the nerve to obturator internus muscle.

Answer 8

• from L5-S2
• exits the pelvis through the greater sciatic foramen inferior to piriformis
• then enters the perineum through the lesser sciatic foramen
• supplies the obturator internus and superior gemellus

Question 9

Describe the nerve to the quadratus femoris muscle.

Answer 9

• from L5-S1
• exits the pelvis through the greater sciatic foramen inferior to piriformis
• supplies the quadratus femoris and inferior gemellus

Question 10

Describe the posterior cutaneous nerve of the thigh.

Answer 10

• from S1-S3
• exits the pelvis through the greater sciatic foramen inferior to piriformis
• sensory to part of the gluteal region and perineum

Question 11

What are the branches of the sacral plexus which supply the pelvis?

Answer 11

1. nerve to piriformis muscle (S1, S2)
2. nerves to levator ani and coccygeus muscles (S3, S4)
3. nerve to external anal sphincter muscle (S4)
4. pudendal nerve (S2-S4)

Question 12

Describe the nerve to piriformis.

Answer 12

• from S1 and S2
• supplies the piriformis
• impingement leads to Piriformis Syndrome, which contributes to Sciatica

Question 13

Describe the nerves to levator ani and coccygeus.

Answer 13

• from S3 and S4
• supply levator ani and coccygeus
• impingement may affect:
  1. integrity of the pelvic floor
  2. urinary continence
  3. fecal continence
  4. parturition

Question 14

Describe the nerve to the external anal sphincter.

Answer 14

• from S4
• supplies the external anal sphincter
• impingement may affect fecal continence

Question 15

Describe the pudendal nerve.

Answer 15

• from S2-S4
• exits the pelvis through the greater sciatic foramen inferior to piriformis
• enters the perineum through the lesser sciatic foramen, traveling in the pudendal canal
• gives off important branches to the perineum
• supplies the external genitalia and underlying musculature; also sensory
• impingement may affect sexual function

Question 16

What are the routes by which sympathetic fibers reach the pelvis?

Answer 16

1. the downward continuation of the sympathetic trunk

2. the downward continuation of the aortic plexus, as the superior hypogastric plexus

Question 17

What is the ganglion impar?

Answer 17

the union of the left and right sympathetic trunks in front of the coccyx

Question 18

What are the components of the pelvic autonomic system?

Answer 18

1. superior hypogastric plexus
2. left and right hypogastric nerves
3. left and right inferior hypogastric plexuses (pelvic plexuses)
4. sacral splanchnic nerves
5. pelvic splanchnic nerves (nervi erigentes)

Question 19

Describe the superior hypogastric plexus.

Answer 19

• the downward continuation of the aortic plexus below the bifurcation of the abdominal aorta
• contains mainly:
  1. sympathetic fibers from the lumbar splanchnic nerve
  2. visceral afferent fibers

Question 20

Describe the left and right hypogastric nerves.

Answer 20

• formed by the superior hypogastric plexus

- two long, narrow nerve plexuses which connect the superior hypogastric plexus to the inferior hypogastric plexus

Question 21

Describe the left and right inferior hypogastric plexuses (pelvic plexuses).

Answer 21

• formed by the union of the hypogastric, pelvic splanchnic, and sacral splanchnic nerves
• they contain:
  1. sympathetic fibers
  2. parasympathetic fibers
  3. visceral afferent fibers

Question 22

What do the inferior hypogastric plexuses give rise to?

Answer 22

subsidiary plexuses which supply pelvic viscera

Question 23

Describe the sacral splanchnic nerves.

Answer 23

preganglionic sympathetic nerves which arise from the sympathetic trunk and synapse in the inferior hypogastric plexus

Question 24

Describe the pelvic splanchnic nerves (nervi erigentes).

Answer 24

• parasympathetic nerves which arise from the sacral segments of the spinal cord (S2-S4)
• they contribute to the formation of the inferior hypogastric plexuses
• supply pelvic viscera