510
UNIT 3
Regulation and Integration of the Body
13
basically reflects the areas supplied by the lumbar and sacral
plexuses, respectively.)
Adjacent dermatomes are not as cleanly separated as a
typical dermatome map indicates. On the trunk, neighboring
dermatomes overlap considerably (about 50%). As a result, de-
struction of a single spinal nerve will not cause complete numb-
ness anywhere. In the limbs, the overlap is less complete and
some skin regions are innervated by just one spinal nerve.
Innervation of Joints
Te easiest way to remember which nerves serve which synovial
joint is to use
Hilton’s law
:
Any nerve serving a muscle that pro-
duces movement at a joint also innervates the joint and the skin over
with spinal cord injuries, you can pinpoint the damaged nerves
and the injured region of the spinal cord by determining which
dermatomes are affected.
Adjacent dermatomes on the body trunk are fairly uniform
in width, almost horizontal, and in direct line with their spi-
nal nerves
(Figure 13.13)
. Te dermatome arrangement in the
limbs is less obvious. (It is also more variable—different clini-
cians have mapped a variety of areas for the same dermatomes.)
Te skin of the upper limbs is supplied by ventral rami of C
5
±
1
(or ±
2
). Te lumbar nerves supply most of the anterior sur-
faces of the thighs and legs, and the sacral nerves serve most
of the posterior surfaces of the lower limbs. (Tis distribution
C2
C3
C4
C5
T1
T2
T2
T3
T4
T5
C6
C8
C7
C7
C6
T6
T7
T8
T9
T10
T11
T12
L1
S2
S3
L1
L2
L3
L4
L5
L2
L3
L4
L5
S1
C5
C6
C8
T2
C5
C6
S1
(a) Anterior view
C2
C3
C4
C5
C6
C7
C8
C8
C8
C7
C7
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L3
S1
(b) Posterior view
L5
S2
S1
S1
S3
S2
S1
S2
S4
S5
L5
L5
L4
L5
L5
L4
C6
C6
C5
L4
L3
L2
L1
L4
Figure 13.13
Map of dermatomes.
Each dermatome is the skin segment innervated by the
cutaneous sensory branches of a single spinal nerve. All spinal nerves except C
1
participate in
the innervation of the dermatomes.
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