Human Anatomy Vol 1

CUIANEOUS NERVES, SUPERFICIAL VEINS AND LYMPHATIC DRAINAGE

for touch, pain and temperature. Note that injury

to a peripheral nerve produces sensory loss

corresponding to the area of distribution of that

neIve.

o The spinal segments do not lie opposite the

corresponding vertebrae. In estimating the

position of a spinal segment in relation to the

surface of the body, it is important to remember

that a vertebral spine is always lower than the

corresponding spinal segment. As a rough guide

it maybe stated that in the cervical region there is

a difference of one segment, e.g. the 5th cervical

spine overlies the 5th cervical spinal segment.

Spinal segments

C1_C8

T1_T6

T7112

L1_L5

S1-S5 and Co1

Spine of vertebra

CI_C7

T1_T4

T5_T9

T10-T11

T12-L1,

In the upper limb, the thumb and radius lie along the

preaxial border, and the little finger and ulna along

the postaxial border.

The dermatomes of the upper limb are distributed

in an orderly numerical sequence (Figs7.6a and b).

a. Along the preaxial border from above downward,

by segments C3-C6 with overlapping of the

dermatomes.

b. The middle three digits (index, middle and ring

fingers) and the adjoining area of the palm are

supplied by segment C7.

c. The postaxial border is supplied (from below

upwards) by segments C8, T7, T2. There is

overlapping of the dermatomes.

As the limb elongates it rotates laterally and gets

adducted and the central dermatome C7 gets pulled

in such a way that these are represented only in the

distal part of the limb, and are buried proximally.

On the front of the limb, areas supplied by C5 and

C6 segments adjoin the areas supplied by CB, T1 and

T2 segments. There is a dividing line between them,

known as the aentral axial line along which C7 is

buried proximeilly. It reaches the skin just proximal

to the wrist (Fig. 7.6a).

On the back of the limb, C7 reaches the skin just

proximal to the elbow. So the dorsal axinl line ends

more proximal to the ventral axial line. There is no

overlapping across the ventral and dorsal axial lines

(Fig.7.6b).

Superficial veins of the upper limb assume importance

in medical practice because these are most commonly

used for intravenous injections and for withdrawing

blood for testing.

Generol Remolks

1 Most of the superficial veins of the limb join together

to form two large veins, cephalic (preaxial) and

basilic (postaxial). An accessory cephalic vein is often

present.

2 The superficial veins run away from pressure points.

Therefore, they are absent in the palm (fist area),

along the ulnar border of the forearm (supporting

border) and in the back of the arm and trapezius

region (resting surface). This makes the course of the

veins spiral, from the dorsal to the ventral surface of

the limb.

3 The preaxial vein is longer than the postaxial. In other

words, the preaxial vein drains into the deep

(axillary) vein more proximally (at the root of the

limb) than the postaxial vein which becomes deep

in the middle of the arm.

4 The earlier a vein becomes deep the better, because

the venous return is then assisted by muscular

compression. The load of the preaxial (cephalic) vein

is greatly relieved by the more efficient postaxial

(basilic) vein through a short circuiting channel (the

median cubital vein situated in front of the elbow)

and partly also by the deep veins through a

perforator vein connecting the median cubital with

the deep vein.

o The area of sensory loss of the skin, following

injuries of the spinal cord or of the nerve roots,

conforms to the dermatomes. Therefore, the

segmental level of the damage to the spinal cord

can be determined by examining the dermatomes

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Fig. 7.5: Overlapping of the dermatomes