Lumbar and sacral plexus

1. Lumbar
and sacral
plexuses

2. Nerve plexuses
• Networks of successive
ventral rami that
exchange fibers
(crisscross & redistribute)
– Why would this be
protective?
• Mainly innervate the
limbs
• Thoracic ventral rami do
not form nerve plexuses

3. Plexuses
• Cervical
• Brachial
• Lumbar
• Sacral

4. Lumbar plexus
• L1-L4
• Lies within the psoas major muscle
• Innervates anterior and medial muscles of
thigh through femoral and obturator nerves
respectively
• Femoral nerve also innervates skin on
anterior thigh (including quads) and medial
leg

5. Diaphragm and posterior abdominal wall:
The psoas major and minor muscles, the quadratus lumborum
muscle. The lumbar plexus and its related nerves.

6. LUMBAR PLEXUS
Spinal nerves branching
from the lumbar region of
the cord form the lumbar
plexus. Branches of this
plexus stimulate muscles
of the back, hip and
thigh. The plexus also is
responsible for sensation
in the skin of the thighs,
the pubic area and the
external genitalia in
males and females.

7. LUMBOSACRAL SPINAL CORD
POSTERIOR VIEW
The area within the rectangle shows
the lower portion of the spinal cord.
The branches leaving the sacral region
pass through the sacral foramina
forming the sacral plexus.

9. 29 Oct. 2012 Spinal-Nerves.ppt 9
Lumbar plexus
• L1 – L4 (+ L5)
• Ilioinguinal nerve
– mostly sensory from
skin of thigh &
genitals
• Genitofemoral nerve
– mostly sensory from
scrotum, labia majora,
ant. Thigh
• Femoral Nerve
– to quadriceps,
sartorius

10. Lumbosacral plexus
Lumbar plexus (T12- L4):
1- Obturator nerve (L2-L3-L4)
2- Femoral nerve (L2-L3-L4)
3- Lumbosacral trunk (L4-L5)
7- subcostal nerve (T12)
8- iliohypogastric N. (T12-L1)
9- ilioinguinal N. (L1)
10- genitofamoral N. (L1-L2)
11- lateral cutaneous N. of the thigh (L2-L3)

11. Lumbar Plexus
• Femoral nerve
– Cutaneous branches
• Thigh, leg, foot (e.g. saphenous nerve)
– Motor branches
• Anterior thigh muscles (e.g. quadriceps,
sartorius, iliopsoas)
• Obturator nerve
– Sensory
• Skin medial thigh; hip, knee joints
– Motor
• Adductor muscles
• Lateral femoral cutaneous
– Sensory
• Skin lateral thigh
• Genitofemoral
– Sensory
• Skin scrotum, labia major, anterior thigh
– Motor
• Cremaster muscle

12. Lumbar plexus
(be able to label femoral, obturator and saphenous
nerves)

13. SACRAL PLEXUS
Spinal nerves branching from
the lumbar (L4 and L5) and
sacral (S1, S2, S3 and S4)
region of the cord form the
sacral plexus.
Nerves branching from
this plexus innervate the limb
and pelvic area. Because the
lumbar and sacral plexuses
are interconnected, they are
sometimes referred to as the
lumbosacral plexus.

14. Sacral plexus
• L4-S4
• Supplies muscles and
skin of posterior thigh
and almost all of the
leg
• Main branch is the
large sciatic nerve,
which consists of:
– Tibial nerve – to most of
hamstrings, calf and sole
– Common fibular nerve –
to muscles of anterior
and lateral leg and skin
• Other branches supply
pelvic girdle (gluteus
muscles) and perineum
(pudental nerve)

15. 29 Oct. 2012 Spinal-Nerves.ppt 15
Sacral plexus
• L4 – S4
• Superior & inferior
gluteal nerves
– To gluteus muscles
• Sciatic nerve
– To hamstrings & other
posterior thigh & leg
muscles
• Pudendal nerve
– Sensory from penis,
clitoris, labia minora,
anus

16. Lumbosacral plexus
Sacral plexus:
Sciatic nerve (roots):
L4
L5
S1
S2
S3
*Sciatic nerve is the thickest nerve of body.
*It is composed of Common Peroneal and
Tibial nerves.
*Com. Peroneal: composed of dorsal rami
Tibial: composed of ventral rami
*L4+L5= Lumbosacral trunk
3- Lumbosacral trunk
4- Sciatic nerve
5- common peroneal N.
6- tibial N.
12- posterior femoral cutaneous nerve
13- pudendal nerve
14- superior gluteal nerve

17. Sacral plexus (L4-S4)
 Sciatic nerve (L4-S3)
 Tibial nerve
 Common peroneal (fibular)
nerve
Motor to muscles of pelvis and lower extremity (gluteal,
posterior femoral, lower leg & foot)
Sensory from posterior pelvis, posterior thigh, anterior,
posterior & lateral leg

19. SCIATIC NERVE
The sciatic nerve (astrerisk) is formed
from spinal nerves arising from the
lumbar (L4 and L5) and sacral (S1, S2
and S3) regions of the spinal cord. It
passes into the thigh and lower leg
supplying innervation of sensation and
movement for the entire lower limb.
When giving a gluteal intramuscular
injection, it is important to inject into
the gluteus medius muscle to avoid
damage to this large nerve.

20. Sacral Plexus
• Sciatic
– Motor:
• Hamstring
– Branches into:
• Tibial nerve
– Cutaneous
» Posterior leg and sole of foot
– Motor
» Posterior leg, foot
• Common fibular (peroneal) nerve
– Cutaneous
» Anterior and lateral leg, dorsum foot
– Motor
» Lateral compartment, tibialis anterior,
toe extensors
• Superior gluteal nerve
– Motor
• Gluteus medius and minimus, tensor
fasciae latae

21. Sacral Plexus (continued)
• Inferior gluteal nerve
– Motor
• Gluteus maximus
• Posterior femoral
cutaneous nerve
– Sensory
• Inferior buttocks, posterior
thigh, popliteal fossa
• Pudendal nerve
– Sensory
• External genitalia, anus
– Motor
• Muscles of perineum

23. • The only one of the three that travel below
the knee is the sciatic nerve.
• The sciatic nerve branches into two nerve:
1. tibial nerve
2. common peroneal nerve
a. Superficial peroneal nerve
b. Deep peroneal nerve

24. femur
medial
lateral
Anterior compartment-
Extensors of the knee
Femoral Nerve
Medial compartment-
Adductors of the knee
Obturator Nerve
Posterior
compartment-
Flexors of the
knee
Sciatic Nerve

25. L2
L3
L4
iliopsoas
Rectus
femoris
pectineus
Vastus
medialis
Vastus
intermedius
sartorius
Vastus
lateralis
Motor Branches of the
Femoral Nerve

26. Adductus magnus
gracilis
Adductor
longus
Adductor
brevis
Motor Branches of the
Obturator Nerve

27. L4
L5
S1
S2
S3
Semitendinosis
Biceps femoris
semimembranosus
Hamstrings
Gastrocnemius
and posterior
compartment of
the leg and foot
Tibial
nerve
Common
peroneal
nerve Deep peroneal
nerve
Anterior
compartment of
leg
Lateral
compartment of leg
Superficial peroneal
nerve
Motor Branches of the
Sciatic Nerve

28. • Sacral plexus
nerves:
(Be able to label
sciatic, tibial and
common fibular
nerves)

29. Diaphragm?
Phrenic nerve C3-5
Arm and forearm extensors?
Radial nerve
Medial hand?
Ulnar nerve
Lateral palm?
Median nerve
Quad?
Femoral nerve
Footdrop?
Common fibular/peroneal nerve
(branch of Sciatic nerve)
Cervical plexus C1-5
Brachial plexus C5-T1
Lumbar plexus L1-4
Sacral plexus L4-S4
Nerve plexuses (very) simplified….

30. Dermatomes (innervation of skin)
Dermatomes
(area of skin innervated by the
cutaneous branches from a single
spinal nerve is called a dermatome)
Reveal sites of
damage to spinal
nerves or spinal cord