Nerves - Sciatic

Question 1

What are the nerve roots of the sciatic nerve?

Answer 1

L4, L5, S1, S2, S3

Question 2

Motor function?

Answer 2

Innervates the muscles of the posterior thigh (biceps femoris, semimembranosous and semitendinosus), hamstring portion of the adductor magnus (remaining portion is supplied by the obturator nerve).

Indirectly, innervates the muscles of the leg and foot.

Question 3

Sensory functions?

Answer 3

No direct sensory function.

Indirectly innervates skin of the lateral leg, heel, and both the dorsal and plantar surfaces of the foot.

Question 4

Anatomical course of the sciatic nerve

Answer 4

Leaves the pelvis and enters the gluteal region, via the greater sciatic foramen.

It emerges either inferior or through the piriformis muscle and descends in an inferoposterior direction.

As the nerve passes through the gluteal region, it crosses the posterior surface of the superior gemellus, obturator internus, inferior gemellus, and quadratus femoris muscles. It enters the posterior thigh by passing deep to the long head of the biceps femoris.

When the sciatic nerve reaches the apex of popliteal fossa, it bifurcates into the tibial and common fibular nerves.

Question 5

Clinical relevance: intramuscular injections

Answer 5

Intramuscular injections are only given to the upper quadrant of the gluteal region to avoid damaging the nerve.