Spinal Nerves

Spinal nerves

• 31 pairs arise from spinal cord

• Five groups correspond to regions of spinal cord and vertebrae– Cervical 8 pr.– Thoracic 12 pr.– Lumbar 5 pr.– Sacral 5 pr.– Coccygeal 1 pr.

Structure of a Nerve

• Bundle of axons • Layers of

connective tissue– Epineurium – Perineurium – Endoneurium

Structure of a spinal nerve

• Tree analogy• Dorsal root & ventral

root fuse lateral to dorsal root ganglion

• Whole nerve "trunk" lies in intervertebral foramen

Structure of a spinal nerve

• Branches • Dorsal ramus• Ventral ramus• Communicating rami

to sympathetic chain ganglion (ANS)

Spinal Nerve Plexuses

Spinal Nerve Plexuses

• Ventral rami of spinal nerves fuse and form networks with ventral rami of other spinal nerves.– Crossing of fibers

• A peripheral nerve may contain axons from several spinal segments.

• T2 – T12 do not form plexuses

Spinal Nerve Plexuses

• Cervical plexus• Brachial plexus• Lumbar plexus• Sacral plexus

Cervical plexus

• C1 – C4 (+ C5)– cutaneous nerves, mostly sensory from skin of neck & back

of head– Phrenic nerve to diaphragm

• Motor stimulation for breathing!

Brachial plexus• C5 – T1

• Complex fusion, splitting, fusion, & division into nerves

• Axillary Nerve– to deltoid

• Musculocutaneous nerve– to biceps brachii,

brachialis

Brachial plexus

• Radial nerve– to triceps brachii, extensors of wrist, hand, fingers

• Wrist drop

• Median nerve– to flexors of wrist, hand, fingers– can be compressed

• Carpal Tunnel Syndrome

• Ulnar nerve – (“funny bone”)– to flexors in hand

• “Claw hand”

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

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