Sciatic Nerve

Question 1

What shape is the sciatic nerve?

Answer 1

A thick, flat band, approx 2cm wide

Question 2

What are the nerve roots of the sciatic nerve?

Answer 2

L4-S3

Question 3

What are the motor functions of the sciatic nerve?

Answer 3

Innervates the muscles of the posterior thigh and the hamstring portion of the adductor magnus
 Indirectly innervates (via its terminal branches) the muscles of the leg and foot

Question 4

What are the sensory functions of the sciatic nerve?

Answer 4

No direct sensory functions
 Indirectly innervates (via its terminal branches) the skin of the lateral leg, heel, and both of the dorsal and plantar surfaces of the foot

Question 5

What is the sciatic nerve derived from?

Answer 5

The lumbosacral plexus

Question 6

What anatomical course does the sciatic nerve take?

Answer 6

After its formation, it leaves the pelvis and enters the gluteal region via the greater sciatic foramen
It emerges inferiorly to the piriformis muscle and descends in an inferolateral direction
As the nerve moves through the gluteal region, it crosses the posterior surface of the superior gemellus, obturator internus, inferior gemellus and quadratus femoris muscles
It then enters the posterior thigh by passing deep to the long head of the biceps femoris

Question 7

What happens to the sciatic nerve in the posterior thigh?

Answer 7

It gives rise to branches to the hamstring muscles and adductor magnus

Question 8

When does the sciatic nerve terminate?

Answer 8

When it reaches the apex of the popliteal fossa

Question 9

How does the sciatic nerve terminate?

Answer 9

By bifurcating into the tibial and common fibular nerves

Question 10

What can the sciatic nerve be described as?

Answer 10

Two individual nerves bundled together in the same connective sheath- the tibial and common fibular nerve

Question 11

When do the tibial and common fibular nerves separate?

Answer 11

Usually at the apex of the popliteal fossa

In approx 12% of people, separate as they leave the pelvis

Question 12

When must the anatomical course of the sciatic nerve be considered?

Answer 12

When administering intramuscular injections into the gluteal regions

Question 13

How can the gluteal region be divided?

Answer 13

Into quadrants, using two lines, marked by bony landmarks-
One line descends vertically from the highest point on the iliac crest
The other horizontal line passes through the vertical line half way between the highest point on the iliac crest and ischial tuberosity

Question 14

Regarding quadrants, where does the sciatic nerve pass?

Answer 14

Through the lower medial quadrant

Question 15

What must be done to avoid damaging the sciatic nerve?

Answer 15

Intramuscular injections are given only in the upper lateral quadrant of the gluteal region

Question 16

What muscles does the sciatic nerve directly innervate?

Answer 16

The muscles in the posterior compartment of the thigh, and the hamstring portion of the adductor magnus

Question 17

How does the sciatic nerve indirectly innervate other muscles?

Answer 17

Via its two terminal branches, the tibial nerve and the common fibular nerve

Question 18

What muscles does the tibial nerve innervate?

Answer 18

The muscles of the posterior leg (calf muscles), some of the intrinsic muscles of the foot

Question 19

What muscles does the common fibular nerve innervate?

Answer 19

The muscles of the anterior leg, lateral leg, and the remain intrinsic foot muscles

Question 20

In total, how much of the lower limb does the sciatic nerve innervate?

Answer 20

Muscles of the posterior thigh, entire leg and entire foot

Question 21

Does the sciatic nerve have any direct cutaneous function?

Answer 21

No

Question 22

How does the sciatic nerve provide indirect sensory innervation?

Answer 22

Via its terminal branches, the tibial nerve and common fibular nerve

Question 23

What does the tibial nerve innervate?

Answer 23

The posterolateral and anterolateral sides of the leg

The plantar surface of the foot

Question 24

What does the common fibular nerve innervate?

Answer 24

The lateral leg and dorsal surface of foot