Sacral plexus (dave's notes)

Question 1

Describe the sacral plexus

Answer 1

The sacral plexus is a flat triangular formation on the front of piriformis from the lumbosacral trunk and the upper four sacral nerves. There are six branches ??before dividing, then three from anteriorly and three from posteriorly??

Question 2

What nerve do nerve roots S1 and S2 create?

Answer 2

Nerve to piriformis. Twigs pass back into the muscle

Question 3

What nerve do nerve roots S2 and S3 create?

Answer 3

The perforating cutaneous nerve which supplies skin over the lower medial side of the buttock

Question 4

List the three groups of the sacral plexus

Answer 4

Six branches of the plexus, then branches of the anterior division of the anterior rami, and branches of the posterior division of the anterior rami

Question 5

From which division does the inferior gluteal nerve arise?

Answer 5

The posterior division of the anterior rami

Question 6

List the six nerves of the sacral plexus and their nerve roots

Answer 6

Nerve to piriformis S1 S2
The perforating cutaneous nerve S2,3
Posterior femoral cutaneous S2,3
Pelvic splanchnic S2,3,4
Pudendal S2,3,4
Perineal branch of S4 - S4

Question 7

List the branches of the anterior division of the anterior rami, and their nerve roots

Answer 7

Nerve to quadratus femoris L4,5, S1
Nerve to obturator internus L5, S1
Tibial part of the sciatic nerve, all five divisions

Question 8

List the branches of the posterior division of the anterior rami and their nerve roots

Answer 8

Superior gluteal nerve L4,5,S1
Inferior gluteal nerve L5, S1, S2
Common perineal (fibular part of sciatic) L4, L5, S1, S2

Question 9

Describe the course of quadratus femoris

Answer 9

Runs down deep in contact with the bone to sink into quadratus femoris

Question 10

Describe the course of the nerve to obturator internus

Answer 10

Passes below prifomis, curls around the base of the ischial spine and sinks into obturator internus, supplying the superior gemellus

Question 11

Describe the course of the superior gluteal nerve

Answer 11

Passes back around the sciatic notch above piriformis between gluteus medius and maximus, supplying both

Question 12

Describe the course of the inferior gluteal nerve

Answer 12

Passes back below piriformis and sinks into gluteus maximus

Question 13

Describe the origin of the common perineal nerve

Answer 13

Formed from four posterior divisions, joins the tibial nerve in the pelvis forming the sciatic nerve

Question 14

Describe the course of the posterior femoral cutaneous nerve

Answer 14

Runs down below piriformis on the sciatic nerve. Remains beneath the fascia and has a series of perforating branches supplying from the buttock to the mid calf

Question 15

Describe the pelvic splanchnic nerve. What does it supply?

Answer 15

Sacral parasympathetic outflow with contributions to the iliohypogastric plexus. Motor to the bladder and sigmoid, descending colon and causes erection.

Question 16

Describe the course and branches of the pudendal nerve.

Answer 16

Enters the pudendal canal being the nerve to the pelvic floor and perineum. Has inferior rectal, perineal and dorsal nerve branches.

Question 17

What does the perineal branch of S4 supply?

Answer 17

Levator ani, skin at the anal margin, and has sympathetic fibres hitch hiking to reach the dartos muscle.