Sciatic nerve

Question 1

What are the nerve roots, motor and sensory function of the sciatic nerve?

Answer 1

Roots: L4-S3
Motor: innervates muscles of posterior thigh & hamstring of adductor magnus, terminal branch innervates muscles of leg & foot
Sensory: indirectly innervate (terminal branches) skin of lateral leg, heel, dorsal & plantar surfaces of foot

Question 2

What are the significance of the sciatic nerve?

Answer 2

the largest nerve of the body
major nerve of lower limb
thick flat band - 2cm

Question 3

What is the sciatic nerve derived from and name the beginning of it’s anatomical course

Answer 3

from lumbosacral plexus
leaves pelvis to enter gluteal region via sciatic foramen
travels down thigh inferior to piriformis muscle, inferolaterally

Question 4

Describe the anatomical course of the sciatic nerve from the gluteal region to the thigh

Answer 4

after passing posterior to gluteus minimis and piriformis, the sciatic nerve then crosses the posterior surface of the superior gemellus, obturatus externus, inferior gemellus, obturator internus, quadratus femoris (all deep muscles of gluteal region), entering posterior thigh by passing deep to long head of biceps femoris

Question 5

What happens once the nerve is in the posterior thigh?

Answer 5

gives rise to nerve branches innervating the hamstring muscles and part of the adductor magnus
when nerve enters popliteal region, it bifurcates into the tibial and common fibular nerves

Question 6

describe the sciatic nerve

Answer 6

2 individual nerve bundles (common fibular & tibial)
normally separated at apex of popliteal fossa
can separate as they leave the pelvis in some people

Question 7

Intramuscular injections

Answer 7

careful to avoid the sciatic nerve - split gluteal region into 4 sections by 2 lines
vertical line: from highest point of iliac crest
horizontal: passes vertical line halfway between highest point of iliac crest and ischial tuberosity (sitting bones)
inject through the upper lateral quadrant as the sciatic nerve runs through the lower medial quadrant

Question 8

motor functions of sciatic nerve

Answer 8

muscles of posterior thigh, hamstring of adductor magnus

Question 9

What are the 2 terminal branches of the sciatic nerve?

Answer 9

tibial

common fibular

Question 10

what are the motor functions of tibial nerve?

Answer 10

muscles of the posterior leg (calf muscles)

some intrinsic muscles of the leg

Question 11

What are the motor functions of the common fibular nerve?

Answer 11

muscles of anterior and lateral leg

remaining instrinsic foot muscles not innervated by the tibial muscle

Question 12

including the terminal branches (tibial & common fibular nerve) which areas of the lower limb is the sciatic nerve responsible for motor functions of?

Answer 12

posterior thigh, entire leg & entire foot

Question 13

does the sciatic nerve have any sensory functions?

Answer 13

not directly, but indirectly through the common fibular and tibial nerves

Question 14

sensory innervation of the tibial nerve

Answer 14

postero-lateral & antero-lateral sides of the leg, plantar surface of foot (sole)

Question 15

sensory function of common fibular nerve

Answer 15

lateral leg & dorsal foot (top of foot)

Question 16

What are the 4 sciatic nerve branches responsible for sensory?

Answer 16

1. sural nerve (branches of common fibular & tibial postero-lateral)
2. deep fibular nerve (branch of common fibular for proximal lateral leg)
3. superficial fibular nerve (branch of common fibular for lower lateral leg)
4. medial calcaneal branches (branches of tibial for plantar foot)