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
• 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
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