Spinal Nerves - Lumbar and Sacral Plexuses

Question 1

Lumbar Plexus - Function, Formation and Nerves

Answer 1

Supplies the skin and musculature of the lower limb.
Formed by ventral rami of L1, L2, L3 and L4 nerves that divide into cord.
Cords combine to form 6 major peripheral nerves:
- Iliohypogastric nerve
- Ilioinguinal nerve
- Genitofemoral nerve
- Lateral cutaneous nerve of the thigh
- Obturator nerve

Question 2

Lumbar Plexus - Iliohypogastric Nerve

Answer 2

Roots: L1 (T12 for some)
Motor function: transversus abdominis, internal oblique.
Sensory function: Posterolateral gluteal skin in pubic region.

Question 3

Lumbar Plexus - Ilioinguinal Nerve

Answer 3

Root: L1
Motor function: (with iliohypogastric) transversus abdominis, internal oblique.
Sensory function: upper middle thigh. Male: root of penis and anterior scrotum. Female: mons pubis and labia majora.

Question 4

Lumbar Plexus - Genitofemoral Nerve

Answer 4

Roots: L1 and L2.
Divides into genital branch and femoral branch after psoas major.
Motor function: Genital branch: cremaster (only male).
Sensory function:
Genital branch: Males: anterior scrotum. Female: mons pubis and labia majora.
Femoral branch: upper anterior thigh.

Question 5

Lumbar Plexus - Lateral Cutaneous Nerve

Answer 5

Roots: L2 and L3
Motor function: none.
Sensory function: anterior and lateral thigh down to knee.

Question 6

Lumbar Plexus - Obturator Nerve

Answer 6

Roots: L2, L3, L4
Motor Function: obturator externus, pectineus, adductor longus, brevis, magnus, gracilis.
Sensory Function: medial thigh.

Question 7

Lumbar Plexus - Femoral Nerve

Answer 7

Roots: L2, L3, L4.
Motor function: iliacus, pectineus, sartorius, quadriceps femoris muscles.
Sensory function: medial and lateral branches of anterior cutaneous of the thigh: anterior thigh and medial leg.
Saphenous nerve: front and side of knee, leg and foot down to base of big toe.

Question 8

Sacral Plexus - Function, Formation and Nerves

Answer 8

Supplies the skin and muscles of the pelvis and lower limb.
Formed by ventral rami of S1, S2, S3 and S4 nerves. Can have contributions from L4, L5.
5 major peripheral nerves:
- Superior gluteal nerve Inferior gluteal nerve
- Sciatic nerve
- Posterior femoral cutaneous nerve
- Pudendal nerve
Leave pelvis via greater sciatic foramen.

Question 9

Sacral Plexus - Superior Gluteal Nerve

Answer 9

Roots: L4, L5, S1
Motor function: gluteus minimus, medius, tensor fascia lata.
Sensory function: none.

Question 10

Sacral Plexus - Inferior Gluteal Nerve

Answer 10

Roots: L5, S1, S2.
Motor function: Gluteus max.
Sensory function: none

Question 11

Sacral Plexus - Posterior Femoral Cutaneous Nerve

Answer 11

Roots: S1, S2, S3.
Motor function: none
Sensory function: posterior thigh and leg. Skin of perineum.

Question 12

Sacral Plexus - Pudendal Nerve

Answer 12

Roots: S2, S3, S4.
Motor function: Skeletal muscles in perineum, external urethral sphincter, external anal sphincter, levator ani.
Sensory function: penis and clitoris. skin of perineum.

Question 13

Sacral Plexus - Sciatic Nerve - Division and Roots

Answer 13

Biggest, goes through sciatic foramen. Divides at the knee: tibial and fibular nerves.
4 pathways: through piriformis, anterior, posterior or medial to piriformis.
Roots: L4 to S3.

Question 14

Sacral Plexus - Sciatic Nerve - Motor Functions

Answer 14

Tibial Portion: Muscles in posterior compartment of thigh and hamstring component of adductor magnus. Muscles in posterior compartment of leg and sole of foot.
Fibular portion: Short head of biceps femoris. Muscles in anterior and lateral compartments of leg and extensor digitorum brevis.

Question 15

Sacral Plexus - Sciatic Nerve - Sensory Functions

Answer 15

Tibial portion: posterolateral and medial surface of foot and sole of foot.
Fibular portion: anterolateral surface of leg and dorsal foot.

Question 16

Sciatic Nerve - Common Peroneal (fibular) Nerve - Cutaneous Branches

Answer 16

Lateral sural cutaneous nerve: upper 2/3 of lateral leg.
Sural communicating nerve: posterolateral calf and joins sural nerve.

Question 17

Sciatic Nerve - Common Peroneal (fibular) Nerve - Motor Branche

Answer 17

Superficial peroneal nerve: fibularis longus, brevis.
Deep peroneal nerve: tibialis anterior, extensor digitorum longus, extensor hallucis longus and some intrinsic muscles of the foot.

Question 18

Sciatic Nerve - Tibial Nerve - Cutaneous Branches

Answer 18

Sural nerve: (merges with fibular nerve) posterolateral side of leg and lateral side of foot.
Medial calcaneal branches: heel.
Medial plantar nerve: plantar surface of medial 3,5 digits and associated sole area.
Lateral plantar nerve: plantar surface of lateral 1,5 digits and associated sole area.

Question 19

Sciatic Nerve - Tibial Nerve - Motor Branches

Answer 19

Posterior compartment of the leg: popliteus, flexor hallucis longus, flexor digitorum longus, tibialis posterior, plantaris, soleus, gastrocnemius.