SPINAL NERVES

I.   INTRODUCTION
–  A spinal nerve comes directly off of the spinal cord

–  31 pairs of spinal nerves

– on each side: 8 cervical spinal nerves, 12 thoracic spinal nerves, 5 lumbar spinal nerves, 5 sacral spinal nerves, and 1 coccygeal spinal nerve

II.  REVIEW OF SPINAL NERVE STRUCTURE
–  each spinal nerve is formed from:

1.  anterior (ventral) root: axons from motor neurons

2.  posterior (dorsal) root:  axons from sensory neurons

– when an anterior root and a posterior root unite, they form a spinal nerve
* motor and sensory

*  spinal nerves have two main branches:

1.  posterior (dorsal) ramus:
*  innervates skin of back, deep back muscles

2.  anterior (ventral) ramus:
*  innervates everything else from the neck inferiorly! 

*  also forms nerve plexuses
–  def. of nerve plexus: a network of converging and/or diverging nerve fibers

III. CERVICAL PLEXUS
–  anterior (ventral) rami of C1-C4

–  innervates the following:

1.  sensory: SKIN of neck, ear and shoulders
2.  motor: anterior neck muscles

–  phrenic nerve (receives SOME axons from cervical plexus)
* C3-C5

*  supplies diaphragm

IV.  BRACHIAL PLEXUS
–  anterior (ventral) rami of C5-T1
–  primarily innervates upper limb

– each nerve has both motor & sensory components

A.  Axillary Nerve:
– sensory:
–  motor:  deltoid and teres minor

B.  Musculocutaneous Nerve:       
– sensory:
–  motor: most muscles on anterior surface of ARM:

1.  coracobrachialis

2.  biceps brachii

3.  brachialis

C.  Radial Nerve:
– sensory:
–  motor:

1.  posterior ARM muscles

2.  posterior FOREARM muscles

D.  Median Nerve:
–  sensory: 
–  motor:

1.  Most anterior FOREARM muscles

2.  THENAR muscles in palm

3.  lumbricals going to fingers 2, 3

E.  Ulnar Nerve:
–  sensory: 
–  motor:

1.  1 ½ anterior FOREARM muscles:

a.  medial ½ of flexor digitorum profundus
b.  flexor carpi ulnaris

2.  most intrinsic hand muscles:

a.  hypothenar muscles

b.  lumbricals to fingers 4, 5   

c.  palmar and dorsal interossei

V.   LUMBAR PLEXUS
–  anterior (ventral) rami of L1-L4
–  innervates inferior abdominal wall, part of lower limb
– each nerve has motor and sensory components

A.  Femoral Nerve:
–  sensory:

–  motor:  anterior thigh muscles

B.  Obturator Nerve:
–  sensory:

–  motor:  medial thigh muscles

VI.  SACRAL PLEXUS
–  anterior (ventral) rami of L4-S4

–  innervates buttocks, pelvic structures, and majority of lower limb

A.  Sciatic Nerve:

–  splits into:

1.  Tibial Nerve
–  sensory:
–  motor:

a.  most posterior thigh muscles (hamstrings)

b.  posterior leg muscles

c.  muscles on sole of foot

 

2.  Common Fibular Nerve:
–  sensory:
–  motor:

a.  anterior leg muscles

b.  lateral leg muscles

 

c.  muscles on dorsum of foot

Which nerve most likely would be damaged if you were unable to flex your forearm/elbow joint?

a.   axillary nerve

b.   median nerve

c.   radial nerve

d.   musculocutaneous nerve

e.   ulnar nerve

Back to A215 home page