LUMBAR PLEXUS REVIEW

Question 1

What are the ROOTS OF THE LUMBAR PLEXUS

Answer 1

Ventral Rami L1-L4 + a branch of the SUBCOSTAL NERVE (T12)

Question 2

Name 1 of the DIRECT BRANCHES of LUMBAR PLEXUS and what it innervates? (1 of 7)

Answer 2

1) ILIOHYPOGASTRIC NERVE (L1)
INNERVATION: muscles of ANTEROLATERAL
ABDOMINAL WALL; skin of INF. ABDOMEN &
BUTTOCK

DESCRIPTION: emerges from superolateral border
Psoas major, crosses obliquely in front Quadratus
lumborum to Iliac crest.
-then perforates posterior Transversus abdominis and
divides b/w that muscle and Obliquus internus
abdominis into LATERAL and ANT. CUTANEOUS
BRANCH

Question 3

Name 1 of the DIRECT BRANCHES of LUMBAR PLEXUS and what it innervates? (2 of 7)

Answer 3

2) ILIOINGUINAL NERVE (L1)
INNERVATION: Muscles of anterolateral
ABDOMINAL WALL, SKIN of sup. & med. aspects
of THIGH, ROOT of PENIS and SCROTUM (male) and
LABIA MAJORA and MONS PUBIS (female).

DESCRIPTION: Emerges from LAT. border of Psoas
major, just inferior to iliohypogastric, passing
obliquely across Quadratus Lumborum and Iliacus,
perforates Transversus abdominis, near anterior iliac
crest, and communicates with Iliohypogastric N. b/w
Transverus and Obliquus internus.
-Nerve then pierces Ob. internus distributing filaments
to it, accompanying Spermatic cord thru
subcutaneous Inguinal ring, is distributed to skin of
Upper & Medial thigh to skin over Root of Penis
and upper part of Scrotum or skin covering MonsPubis
and Labia (female)

Question 4

Name 1 of the DIRECT BRANCHES of LUMBAR PLEXUS and what it innervates? (3 of 7)

Answer 4

3) GENITOFEMORAL NERVE (L1/L2)
INNERVATION: CREMASTER MUSCLE; skin over middle
anterior surface of thigh, scrotum(m), labia majora(f)

DESCRIPTION: passes obliquely thru Psoas major,
emerging from its medial border close to vert. column
b/w L3/4
-it descends on surface of Psoas maj. under cover of
peritoneum and divides into EXTERNAL SPERMATIC
and LUMBOINGUINAL NERVES
-occasionally these 2 nerves emerge separately thru
the substance of the psoas

Question 5

Name 1 of the DIRECT BRANCHES of LUMBAR PLEXUS and what it innervates? (4 of 7)

Answer 5

4) LATERAL FEMORAL CUTANEOUS NERVE (L2/L3)
INNERVATION: skin over lateral, anterior and posterior
aspects of the thigh.

DESCRIPTION: arises from DORSAL DIVISIONS of the
2nd and 3rd LUMBAR NERVES
-emerges from LATERAL border of Psoas maj. and
crosses iliacus obliquely, t/w ASIS. Then passes
under INGUINAL LIGAMENT and over SARTORIUS
into thigh, where it divides into 2 branches:
ANTERIOR and POSTERIOR.

Question 6

Name 1 of the DIRECT BRANCHES of LUMBAR PLEXUS and what it innervates? (5 of 7)

Answer 6

5) FEMORAL NERVE (L2-L4)
INNERVATION: largest nerve arising from LP
-distributed to FLEXOR MUSCLES of HIP &
EXTENSOR MUSCLES of KNEE, skin over ant. and
med. aspect of thigh and medial side of leg and foot.

DESCRIPTION: arises from DORSAL DIVISION of
2nd, 3rd and 4th LUMBAR NERVES
- descends through fibres of Psoas maj, emerging from
muscle at lower lateral border; passes down b/w it
and Iliacus, behind iliac fascia; runs beneath
INGUINAL LIGAMENT, into THIGH and splits into an
ANT. and POST. DIVISION
-under inguinal lig. its separated from femoral artery by
a portion of Psoas major

Question 7

Name one DIRECT BRANCHES of LUMBAR PLEXUS and what it innervates? (6 of 7)

Answer 7

6) OBTURATOR NERVE (L2-L4)
INNERVATION: motor-ADDUCTOR MUSCLES of hip joint.
sensory-skin over MED. ASPECT of THIGH
specific muscles(3 Ducks Pecking Grass Outside)
ADDUCTOR LONGUS, BREVIS, MAGNUS (ant. head),
PECTINEUS (+ femoral), GRACILIS, OBTURATOR EXT.

DESCRIPTION: arises from VENTRAL DIVISIONS 2nd, 3rd and 4th LUMBAR NERVES.
-3rd branch is largest, 2nd very small.
-descends thru Psoas major, emerges at medial border
near PELVIS, passes behind COMMON ILIAC
VESSELS and on lateral side of HYPOGASTRIC
VESSELS and UTERER, which separate it from ureter,
run along lateral wall of lesser pelvis, above and in
front of OBTURATOR VESSELS to superior part of
OBTURATOR FORAMEN.
-Here it enters THIGH and divides into ANTERIOR and
POSTERIOR BRANCH which are separated at first by
some of the fibres of OBTURATOR EXTERNUS, and
lower down by ADDUCTOR BREVIS

Question 8

Name 1 of the DIRECT BRANCHES of LUMBAR PLEXUS and what it innervates? (7 of 7)

Answer 8

7) occasionally the ACCESSORY OBTURATOR NERVE

(L3/4)