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• The blood supply of the spinal cord: the spinal cord is supplied
any one spinal nerve (a dermatome) can be mapped out and these are
with blood by spinal arteries that are derived from the vertebral, inter-
shown in Fig. 72.1. Knowledge of the dermatome map is of great value
costal, lumbar and lateral sacral arteries. Each artery divides into dor-
in diagnosing lesions of the spinal nerves but it must be remembered
sal and ventral branches that follow the corresponding nerve roots to more than one peripheral nerve. However, the area of skin supplied by
the spinal cord where they form longitudinally arranged anterior and that these areas are subject to some variation from one person to
paired posterior spinal arteries. These longitudinal anastomoses, how- another and there is also a good deal of overlap. Thus a lesion of, say,
ever, are incomplete and the spinal arteries themselves vary in size. The T4 may cause little or no loss of sensation because of overlap with T3
largest are in the lower thoracic and upper lumbar regions, and the and T5.
blood supply of the cord may be jeopardized if some of these larger Similarly, certain groups of muscles (myotomes) can be recognized
spinal arteries are damaged, for example in resection of the thoracic as being supplied by particular spinal nerves. For example, C5 supplies
aorta. the abductors of the shoulder, the flexors of the elbow and the supin-
ators so that a lesion of this nerve or of the upper trunk of the brachial
The spinal nerves plexus will cause the arm to be held in a position of adduction of the
As has been described in Chapter 2, the spinal nerves from T2 to L1 shoulder, extension of the elbow and pronation (Erb–Duchenne para-
supply segmental areas of skin and muscles but elsewhere they form lysis). Similarly, T1 supplies the small muscles of the hand so that a
plexuses so that the areas supplied by each nerve become more complic- lesion of this nerve, due perhaps to the presence of a cervical rib, will
ated. Each named peripheral nerve may contain components of more cause global wasting of the hand muscles.
than one spinal nerve and each spinal nerve may contribute fibres to

The spinal cord 161