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