
Spinal
nerves – 31
pairs,
emerging at
each
vertebral
level
Figure 13-10: The Cervical Plexus
Cervical Plexus
Accessory
nerve (XI)
Great auricular nerve
Cranial nerves
Hypoglossal
nerve (XII)
Lesser occipital nerve
Geniohyoid muscle
Transverse cervical nerve
Nerve roots of
cervical plexus
C1
Thyrohyoid muscle
C2
Ansa cervicalis
C3
C4
Omohyoid muscle
C5
Phrenic nerve
Sternohyoid muscle
Supraclavicular nerves
Sternothyroid muscle
Clavicle
Brachial Plexus
Lumbarsacral
plexus
MYOTOMES & DERMATOMES

Myotomes
Each muscle in the
body is supplied
by a particular
level or segment
of the spinal cord
and by its
corresponding
spinal nerve.

Dermatomes
~Greek for"skin
cutting"
~An area of the
skin supplied by
specific nerve
fibers.
Sensory
Dermatomes and Myotomes

Dermatome- sensory region of skin
innervated by a nerve root
 Myotome- muscles innervated by a single
nerve root
Common Dermatomal Levels

C5- Shoulder

C6- Lateral Arm and Digits 1&2

C7- Middle Digit

C8- Digits 4 & 5
Common Dermatomal Levels

L4- Anteromedial Shin

L5- Anterolateral Shin, dorsum of foot to
big toe
Common Dermatomal Levels

S1- toe, lateral foot, sole and calf
ASIA, 2006
Neurologic Level C5


The muscles found
within this myotomal
pattern are the deltoid
and the biceps brachii.
Because the latter is
also innervated by C6,
the deltoid is the most
"pure" C5 muscle.
One of the most
commonly used tests
for shoulder abduction
is to instruct the patient
to flex the elbow at 90
degrees, then offer
gradual resistance to
abduction
Neurologic Level C6

the biceps brachii is
innervated by C5 and
C6. C6 also innervates
the most powerful wrist
extensors, carpi radialis
longus and brevis,
which do radial
extension. To test for
wrist extension,
stabilize the patient’s
forearm and wrist
extension
Neurologic Level C7

The muscles found
within this myotomal
pattern are the triceps,
wrist flexors. The
triceps muscle primarily
does elbow extension.
A common test for this
action is to ask the
patient to fully flex the
arm, offer firm, constant
resistance until
discerning the
maximum resistance
h/she can overcome.
Neurologic Level C8:

The muscles found
within this myotomal
pattern are finger
flexors—flexor
digitorum superficialis,
flexor digitorum
profundis, and the
lumbricals. To test for
finger flexion, the
patient fully flexes h/her
fingers at all joints while
you curl your fingers
into them. Ask the
patient to resist your
attempt to pull h/her
fingers out of flexion.
Neurologic level T1:


The muscles found
within this myotomal
pattern are those
involved in finger
abduction—dorsal
interossei and abductor
digiti minimi, and
adduction—palmar
interossei.
To test for finger
adduction, ask the
patient to extend h/her
fingers and hold a piece
of paper (or a dollar bill)
between two of h/her
fingers. Then you pull it
out
Neurologic Levels T12 to L3:
The muscles found
within this myotomal
pattern are the
iliopsoas, quadriceps,
and the adductors
Because this myotomal
pattern includes
multiple muscle groups
an injury to this nerve
root level can be more
easily evaluated by
sensory testing of the
dermatomal patterns.
Neurologic Level L4:


The muscle
predominantly
innervated at this root
nerve level is the tibialis
anterior, which does
dorsiflexion.
Instruct the patient to
dorsiflex and invert
h/her foot. With your
free hand, hold the
patient’s foot and ask
h/her to resist your
attempt to move the
foot into plantarflexion
Neurologic Level L5:

The muscles found
within this myotome
are the extensor
hallucis longus (big
toe extensor) &
extensor digitorum
(heel walk)
Neurologic Level S1:

The muscles found
within this myotome
are the peroneus
longus (eversion) &
peroneus brevis
(eversion)