Human Anatomy Vol 1

(mdmrcog) #1
UPPER LIMB

Definilion
The area of skin supplied by one spinal segment is
called a dermatome.-R typical dermatome extends
from the posterior median line to the anterior median
line around the trunk (see Fig.5.2). However, in the
limbs the dermatomes have migrated rather irregularly,
so that the original uniform pattern is disturbed.

Embryologicol Bosis
The early human embryo shows regular segmentation
of the body. Each segment is supplied by the
corresponding segmental nerve. In an adult, all
structures, including the skin, developed from one
segmen! are supplied by their original segmental nerve.
The limb may be regarded as an extension of the body
wall, and the segments from which they are derived
can be deduced from the spinal nerves supplying them.
The timb buds arise in the area of the body wall
supplied by the lateral branches of anterior primary
rami. The nerves to the limbs represent these branches
(Fig.7.2).

lmpodonl Feotutes
L The cutaneous innervation of the upPer limb is
derived:
a. Mainly from segments C5-C8 and T1 of the spinal
cord, and

Lower limb bud

Fig.7.2: The body wall is supplied by (A) the posterior primary
rami, (B) the lateral branches of the anterior primary rami, and
(C) the anterior branches of the anterior primary rami of the
spinal nerves. The limb buds develop from the area supplied by
the lateral branches of the anterior primary rami

b. Partly from the overlapping segments from above
(C3, C4) as well from below (T2, T3). The addi-
tional segments are found only at the proximal
end of the limb (Fig.7.3).
Since the limb bud appears on the ventrolateral
aspect of the body wall, it is invariably supplied by
the anterior primary rami of the spinal nerves.
Posterior primary rami do not supply the limb.
It is possible that the ventral and dorsal divisions of
the trunks of the brachial plexus represent the
anterior and posterior branches of the lateral
cutaneous nerves (see Figs 4.1'4, 5.2 and 7.4).
There is varying degree of overlapping of adjoining
dermatomes, so that the area of sensory loss
following damage to the cord or nerve roots is always
less than the area of distribution of the dermatomes
(Fig.7.5).
Each limb bud has a cephalic and a caudal border,
known as preaxial and postaxialborders, respectively.

Fig. 7.3: The upper limb bud grows out opposite C5, C6, C7,
C8 and T1 segments of the spinal cord

Fig.7.4; The upper limb bud grows out from the part of the
body wall supplied by the lateral cutaneous branches of the
anterior primary rami of spinal nerves

Upper mb
bud

ll
tr
5


oCL
CL
D


co
.F
oo
a

Lateral branch of
anterior primary ramus
Free download pdf