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