Summary of Lumbosacral Plexus

Question 1

What spinal nerves LEVELS make up the Lumbar plexus?

Answer 1

ventral rami L1-L4

Question 2

What are the nerves make up the Lumbar plexus?

Answer 2

• Iliohypogastric n. (L1)
• Ilioinguinal n. (L1)
• Genitofemoral n. (L1-L2)
• Lateral cutaneous nerve of the thigh (L2-L3)
• Obturator n. (L2-L4)
• Femoral n. (L2-L4)

Question 3

What does the Iliohypogastric n. (L1) do?

Answer 3

• Sensory: skin of inguinal region and superolateral gluteal region
• Motor: abdominal muscles

Question 4

What does the Ilioinguinal n. (L1) do?

Answer 4

• Sensory: skin of inguinal region, scrotum or labia majora and superomedial thigh
• Motor: abdominal muscles

Question 5

What does the Genitofemoral n. (L1-L2) do?

Answer 5

• Femoral branch: sensory to skin of superomedial thigh

- Genital branch: sensory to skin of scrotum or labia majora AND motor to cremaster muscle

Question 6

What does the Lateral cutaneous nerve of the thigh (L2-L3)?

Answer 6

-Sensory: skin of lateral thigh

Question 7

What does the Obturator n. (L2-L4) do?

Where does it course?

Answer 7

-Emerges medial to psoas major –> Courses along lateral wall of pelvis and exits via obturator canal

• Motor: medial compartment of thigh
• Sensory: skin of medial thigh

Question 8

What does the Femoral n. (L2-L4) do?

Where does it course?

Answer 8

-Emerges lateral to psoas major –> Passes deep to inguinal ligament

• Motor: anterior compartment of thigh
• Sensory: skin of anteromedial thigh, leg, and foot

Question 9

What spinal nerves LEVELS make up the Sacral plexus?

Answer 9

ventral rami L4-S4

Question 10

What are the nerves make up the Sacral plexus?

Answer 10

• Lumbosacral trunk (ventral rami of L4-L5)
• Superior gluteal n.
• Inferior gluteal n.
• Sciatic n. (L4-S3)
• Pudendal n. (S2-S4)

Question 11

What does the Lumbosacral trunk (ventral rami of L4-L5) do? Where does it course?

Answer 11

-Descends medial to psoas major and joins the ventral rami of S1-S4 as they emerge from the anterior sacral foramina (and through piriformis)

Question 12

What does the Superior gluteal n. do?

Where does it course?

Answer 12

• Exits pelvis via greater sciatic foramen superior to piriformis
• Motor: gluteus medius, gluteus minimus, tensor fascia latae

Question 13

What does the Inferior gluteal n. do?

Where does it course?

Answer 13

• Exits pelvis via greater sciatic foramen inferior to piriformis
• Motor: gluteus maximus

Question 14

What does the Sciatic n. (L4-S3) do?

Where does it course?

Answer 14

• Largest nerve in the body
• Exits pelvis via greater sciatic foramen inferior to the piriformis –> Enters gluteal region (but does NOT innervate gluteal muscles)
• Motor: posterior compartment of thigh, all compartments of leg and foot
• Sensory: skin of foot and most of leg

-Note: the sciatic nerve is actually a combination of two nerves, the common fibular (peroneal) nerve and the tibial nerve

Question 15

What does the Pudendal n. (S2-S4) do?

Where does it course?

Answer 15

-Exits pelvis via greater sciatic foramen inferior to piriformis –> Courses around the ischial spine –> Enters the perineum through the lesser sciatic foramen –> Enters the pudendal (Alcock) canal on the lateral wall of the ischioanal fossa

• Motor: muscles of the UG and anal triangles
• Sensory: skin of the UG and anal triangles