Nerves - Sacral Plexus

Question 1

What makes up the sacral plexus?

Answer 1

The sacral plexus is made up of the anterior rami of S1, S2, S3, S4 fibres. They are joined by L4 and L5, which combine to make up the lumbosacral trunk.

Question 2

What nerves are derived from the sacral plexus?

Answer 2

There are 5 periphereal nerves of the sacral plexus:

1) Superior gluteal nerve
2) Inferior gluteal nerve
3) Sciatic nerve
4) Posterior femoral cutaneous
5) Pudendal nerve

Tip: Some Irish Sailor Pesters Polly

Question 3

Superior gluteal nerve

Answer 3

Root - L4, L5, S1

Motor function - gluteus minimus, gluteus medius, and tensor fascia lata

Sensory function - none

Pathway - leaves the pelvis via the great sciatic foramen - enters superior to the piriformis muscle. Accompanied by the superior gluteal artery and vein.

Question 4

Inferior gluteal nerve

Answer 4

Root - L5, S1, S2

Motor function - gluteus maximus

Sensory function - none

Pathway - leaves via the greater sciatic foramen, inferior to the piriformis muscle. Accompanied by the inferior gluteal artery and vein for much of its course.

Question 5

Sciatic nerve

Answer 5

Roots - L4, L5, S1, S2, S3,

Motor function:

Tibial portion - innervates muscles of the posterior compartment (apart from the short head of the biceps femoris) and the hamstring component of the adductor magnus. Innervates all muscles in the posterior compartment of the leg and sole of the foot.

Common fibular portion - short head of the biceps femoris. All muscles in the anterior and lateral compartment, as well as the extensor digitorum brevis.

Sensory functions:

Tibular portion - supplies the skin of the posterolateral leg, lateral foot and sole of the foot.

Common fibular portion - supplies the skin of the lateral leg and dorsum of the foot.

Question 6

Posterior femoral cutaneous

Answer 6

Roots - S1, S2, S3

Motor functions - none

Sensory functions - skin of posterior leg and thigh, as well as the skin of the perineum.

Question 7

Pudendal

Answer 7

Roots - S2, S3, S4

Motor functions - skeletal muscles in the perineum, the external urethral sphincter, the external anal sphincter, levator ani.

Sensory innervation - penis and clitoris and skin of the perineum.

Pathway - leaves the pelvis via the greater sciatic foramen and re-enters via the lesser sciatic foramen. It moves anterosuperiorly along the lateral wall of the ischiorectal fossa and terminates by dividing into several branches.

Tip - S2, 3, 4 keeps shit off the floor!

Question 8

Other branches

Answer 8

Perforating cutaneous nerve - inferior gluteal region

Pelvic splanchnic nerves - abdominal viscera

Nerve to piriformis

Nerve to obturator internus

Nerve to quadratus femoris