Lumbar and sacral plexuses

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

Plexuses

• Cervical

• Brachial

• Lumbar

• Sacral

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

Diaphragm and posterior abdominal wall:The psoas major and minor muscles, the quadratus lumborum

muscle. The lumbar plexus and its related nerves.

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.

LUMBOSACRAL SPINAL CORDPOSTERIOR 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.

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

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)

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

Lumbar plexus(be able to label femoral, obturator and saphenous

nerves)

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.

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)

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

Lumbosacral plexusSacral plexus:Sciatic nerve (roots):L4L5S1S2S3

*Sciatic nerve is the thickest nerve of body.*It is composed of Common Peroneal andTibial nerves.*Com. Peroneal: composed of dorsal rami Tibial: composed of ventral rami

*L4+L5= Lumbosacral trunk

3- Lumbosacral trunk4- Sciatic nerve5- common peroneal N.6- tibial N.12- posterior femoral cutaneous nerve13- pudendal nerve14- superior gluteal nerve

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

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.

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

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

• 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

femurmedial

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

L2

L3

L4

iliopsoas

Rectus femoris

pectineus

Vastus medialis

Vastus intermedius

sartorius

Vastus lateralis

Motor Branches of the

Femoral Nerve

Adductus magnus

gracilis

Adductor longus

Adductor brevis

Motor Branches of the

Obturator Nerve

L4

L5

S1

S2

S3

Semitendinosis

Biceps femoris

semimembranosus

Ham

strin

gs

Gastrocnemius and posterior compartment of the leg and foot

Tibial nerve

Common peroneal nerve Deep peroneal

nerveAnterior compartment of leg

Lateral compartment of leg

Superficial peroneal nerve

Motor Branches of the

Sciatic Nerve

• Sacral plexus nerves:

(Be able to label sciatic, tibial and common fibular nerves)

Diaphragm? Phrenic nerve C3-5

Arm and forearm extensors? Radial nerveMedial hand? Ulnar nerveLateral 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….

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