Lumbar-Sacral Plexus

Question 1

Which spinal nerves contribute to the lumbar plexus?

Answer 1

The anterior rami of L1, L2, L3 and L4 (also contributions from T12)

Question 2

What are the five major peripheral nerves that arise from the lumbar plexus?

Answer 2

Ilioinguinal 
Genitofemoral 
Lateral cutaneous nerve of the thigh
Femoral nerve
Obturator nerve

Question 3

Ilioinguinal nerve

• Nerve root?
• Motor functions?
• Sensory functions?

Answer 3

• Nerve root is L1
• Motor function: innervates internal oblique and transversus abdominis
• Sensory: innervates skin on upper middle thigh, males: skin over root of penis and anterior scrotum, females: skin over mons pubis and labia majora.

Question 4

Genitofemoral nerve

• Nerve roots?
• Motor functions?
• Sensory functions?

Answer 4

• Nerve roots are L1 and L2
• Motor: genital branch of this nerve innervates cremasteric muscle
• Sensory: genital branch - skin of anterior scrotum (males) and skin over mons pubis and labia majora (females). Femoral branch -skin of upper anterior thigh.

Question 5

Lateral cutaneous nerve of the thigh

• Nerve roots?
• Sensory function?
• Motor function?

Answer 5

• Nerve roots are L2 and L3
• No motor functions.
• Sensory: anterior and lateral thigh down to knee

Question 6

Obturator nerve

• Nerve roots?
• Motor functions?
• Sensory functions?

Answer 6

• Nerve roots are L2, L3, L4.
• Motor functions: obturator externus, pectineus, adductor longus, adductor brevis, adductor magnus, gracilis (all perform adduction)
• Sensory: skin over medial thigh

Question 7

Femoral nerve

• Nerve roots?
• Motor functions?
• Sensory functions?

Answer 7

• Nerve roots are L2, L3 and L4
• Motor: illiacus, pectineus, sartorius and all quadriceps muscles.
• Sensory: anterior thigh and medial leg

Question 8

Mnemonic for remembering branches of lumbar plexus: I Get Leftovers On Fridays

Answer 8

I = Ilioinguinal
Get = Genitofemoral
Leftovers = Lateral cutaneous nerve of thigh 
On = Obturator 
Fridays = Femoral

Question 9

In what order top to bottom do the five major peripheral nerves come out of the lumbar plexus?

Answer 9

L1 ilioinguinal
L1 & L2 genitofemoral 
L2 & L3 lateral cutaneous 
L2, L3 & L4 femoral 
L2, L3 & L4 obturator

Question 10

Which spinal nerves contribute to the sacral plexus?

Answer 10

Anterior rami of S1, S2, S3 and S4 (plus contributions from L4 and L5)

Question 11

What are the four major peripheral nerves of the sacral plexus?

Answer 11

Superior gluteal nerve
Inferior gluteal nerve
Sciatic nerve and divisions
Posterior cutaneous nerve of thigh
(Some Irish Sailor Pesters Polly)

Question 12

How do the peripheral nerves of the sacral plexus leave the pelvis?

Answer 12

Via the greater sciatic foramen.

Question 13

Superior gluteal nerve

• Nerve roots?
• Motor functions?
• Sensory functions?

Answer 13

• Nerve roots L4, L5 & S1
• Motor: gluteus minimus, gluteus medium and tensor fascia lata
• No sensory functions

Leaves the pelvis superior to piriformis muscle via greater sciatic foramen.

Question 14

Inferior gluteal nerve

• Nerve roots?
• Motor functions?
• Sensory functions?

Answer 14

• Nerve roots L5, S1 and S2
• Motor: gluteus maximus
• No sensory functions

Enters the gluteal region inferior to piriformis muscle.

Question 15

Sciatic nerve

• Nerve roots?
• Motor functions?
• Sensory functions?

Answer 15

• Nerve roots L4, L5, S1, S2 and S3
• Motor:
  Tibial portion -all muscles of posterior thigh (except short head of biceps femoris), posterior leg and sole of foot.
  Fibular portion -short head of biceps femoris, all muscles in anterior and lateral leg
• Sensory:
  Tibial -skin of posterolateral & medial foot and sole of foot
  Fibular -skin of anterolateral surface of leg, dorsal foot.

Question 16

Posterior Femoral Cutanous

• Nerve roots?
• Motor functions?
• Sensory functions?

Answer 16

• Nerve roots S1, S2 and S3
• No motor functions
• Sensory: skin of posterior thigh and leg, perineum