There are certain general principles about the dis- tribution of nerves to the skin which are of clinical importance.
1. Each nerve which passes to the skin is distributed to a circumscribed area. The area of the upper limb skin supplied by spinal nerves C. 4 to T. 2 is shown in Fig. 5.12.
2. Limb plexuses are formed by the plaiting together of the ventral rami of several spinal nerves. As a result of this: (a) each part of the plexus and each they pierce the fascial floor of the axilla; however,
some lymphatics on the medial aspect enter the superficial cubital nodes, and efferents from these nodes pass through the deep fascia with the basilic vein; (3) a few vessels from the lateral side of the arm and shoulder run with the cephalic vein into the apical axillary nodes; and (4) vessels from the shoulder and upper parts of the thoracic wall curve round the anterior and posterior axillary folds to enter the pectoral and subscapular groups of ax- illary nodes; those from the walls of the lower parts of the thorax and upper abdomen converge directly on the axilla.
Fig. 5.8 Superficial veins and nerves of the back of the upper limb.
Supraclavicular Nn.
Upper lateral cutaneous N. of arm
Lower lateral cutaneous N. of arm
Posterior cutaneous N. of forearm
Lateral cutaneous N. of forearm
Superficial branch of radial N.
Cephalic V.
Dorsal branch of ulnar N.
Basilic V.
Posterior branch of medial cutaneous N. of forearm Medial cutaneous N. of arm Intercostobrachial N.
Posterior cutaneous N. of arm
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Cutaneous nerves of the upper limb
destroyed is different from the loss resulting from the destruction of a ventral ramus.
3. Cutaneous nerves supplying adjacent areas of skin overlap with each other to a considerable degree.
Thus, the destruction of a single cutaneous nerve leads to a total loss of sensation only in a small area within the area of distribution of that nerve.
Surrounding this anaesthetized area, there will be an area of altered sensation due to the presence of nerve fibres from adjacent uninjured nerves.
branch of the brachial plexus contain nerve fibres from more than one ventral ramus—examples: the upper trunk contains fibres from C. 5 and C. 6; the ulnar nerve contains fibres from C. 8 and T. 1; and (b) several of these branches contain some nerve fibres from the same ventral ramus—example: the suprascapular nerve and the axillary nerve con- tain fibres from C. 5 and C. 6 [see Fig. 3.21]. Thus, the area of distribution of a cutaneous nerve, and consequently the area of sensory loss, when it is
Supraclavicular Nn.
Upper lateral cutaneous N. of arm
Cephalic V.
Lower lateral cutaneous N. of arm
Lateral cutaneous N. of forearm
Cephalic V.
Digital N.
Palmaris brevis Palmar cutaneous branch of median N.
Palmar cutaneous branch of ulnar N.
Anterior branch of medial cutaneous N. of forearm
Posterior branch of medial cutaneous N. of forearm
Basilic V.
Basilic V.
Medial cutaneous N. of arm
Medial cutaneous N. of forearm
Fig. 5.9 Superficial veins and nerves of the front of the upper limb.
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The free upper limb
make a detailed diagnosis of the site of an injury depends on knowing the distribution of the indi- vidual cutaneous nerves and the approximate site of origin of these nerves from the parent trunk [see Fig. 10.1].
The diagrams of nerve distribution in this book take no account either of the overlap or of the fact that nerve fibres may sometimes pass to their des- tinations by unusual routes and hence modify the expected clinical effects of destruction of a particu- lar nerve.
5. In both upper and lower limbs, the nerves which pass to the anterior surface supply a greater area of the skin than those which pass to the posterior sur- face. In the upper limb, this means that a greater part of the skin is supplied by nerves arising from the medial and lateral cords of the brachial plexus which are formed from the anterior divisions of the trunks of the plexus.
Dissection 5.2 continues the study of the cutane- ous nerves of the forearm.
Each thoracic spinal nerve (except for T. 1 which is involved in the formation of a plexus) supplies a strip of skin (dermatome) which overlaps those of adjacent nerves, so that destruction of a single thoracic spinal nerve produces only altered sensa- tion within its dermatome. In the plexus regions, each ventral ramus supplies a circumscribed area of skin in sequence with, and overlapped by, the areas of adjacent ventral rami. The overlap of these dermatomes is accounted for by the presence of nerve fibres from multiple ventral rami in every branch of the plexus.
4. Major branches of the plexus, i.e. the main nerves of a limb, give rise to several cutaneous branches which leave them at different points.
Destruction of a nerve before it has given off any branches will produce a different distribution of sensory loss to that which occurs when the nerve is destroyed after giving off one or more branch- es. It is more important to know the total distri- bution of these major nerves than that of their individual cutaneous branches. But the ability to
Brachialis Biceps
Cephalic V.
Radial recurrent A.
Lateral cutaneous N. of forearm Median cephalic V.
Brachioradialis Radial A.
Median V. of forearm Cephalic V.
Pronator teres Deep communicating V.
Ulnar A.
Bicipital aponeurosis Median basilic V.
Brachial A.
Brachialis Median N.
Basilic V.
Medial cutaneous N. of forearm
Basilic V.
Fig. 5.10 Commonly seen arrangement of superficial veins at the bend of the elbow.
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Cutaneous nerves of the upper limb