Human Anatomy Vol 1

(mdmrcog) #1
-Hippocrotes

INIRODUCTION

The superficial fascia seen after the reflection of skin
contains cutaneous nerves, cutaneous or superficial
veins and lymphatics. The cutaneous nerves are the
continuation of the spinalnerves and carry sympathetic
fibres for supplying the sweat glands, arterioles in the
dermis and arrector pilorum muscles in relation to the
hair follicle. Thus, the effects of sympathetic on the skin
are sudomotor (increase sweat secretion); vasomotor
(narrow the arterioles of skin) and pilomotor (contract
arrector pilorum muscle to make the hair erect or
straight) respectively. The nerves also carry sensation
of pain, touch, temperature and pressure. Superficial
veins are seen along with the cutaneous nerves. These
are utilised for giving intravenous transfusions, cardiac
catheterisation and taking blood samples. Lymphatic
vessels are not easily seen in ordinary dissection.


Dissection

Make one horizontal incision in the arm at its junction
of upper one-third and lower two-thirds segments
(see Fig. 3.2) and a vertical incision through the centre
of arm and forearm till the wrist where another
transverse incision is given.
Reflect the skin on either side on the front as well as
on the back of the limb. Use this huge skin flap to cover
the limb after the dissection.

Posilion

The skin of the upper limb is supplied by 15 sets of
cutaneous nerves (Table 7.1). Out of these only one set
(supraclavicular) is derived from the cervical plexus,
and another nerve (intercostobrachial) is derived from
the second intercostal nerve. The remaining 13 sets are


derived from the brachial plexus through the
musculocutaneous, median, ulnar, axillary and radial
nerves. Some branches arise directly from the medial
cord of the plexus.
It should be noted as follows;
a. The areas of distribution of peripheral cutaneous
nerves do not necessarily correspond with those
of individual spinal segments. (areas of the skin
supplied by individual spinal segments are called
dermatomes). This is so because each cutaneous
nerve contains fibres from more than one ventral
ramus (of a spinal nerve); and each ramus gives
fibres to more than one cutaneous nerve.
b. Adjacent areas of skin supplied by different cuta-
neous nerves overlap each other to a considerable
extent. Therefore, the area of sensory loss after
damage to a nerve is much less than the area of
distribution of the nerve. The anaesthetic area is
surrounded by an area in which the sensations are
somewhat altered.
c. In both the upper and lower limbs, the nerves of
the anterior surface have a wider area of
distribution than those supplying the posterior
surface.
The individual cutaneous nerves, from above
downwards, are described below with their root values.
Figure 7.1 shows the cutaneous nerves of the upper
limb.
1 The supraclaaicular neraes (C3, C4) are branches
of the cervical plexus. They pierce the deep fascia
in the neck, descend superficial to the clavicle,
and supply:
a. The skin of the pectoral region up to the level
of the second rib.
b. Skin covering the upper half of the deltoid.
2 The upp er later al cutaneous nerae of the arm (C5, C6)
is the continuation of the posterior branch of the
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