Dermatomes are regions of skin innervated by a single spinal nerve. In the limbs, long strips of skin are innervated by a single segment of the cord.

The neck and hands are innervated by cervical spinal nerves; the legs are innervated by lumbar and upper sacral nerves, while the perineum has innervation from the sacral cord.

There is some overlap between adjacent spinal nerves, so that there is no precise dividing line between dermatomes.

As a consequence division of one spinal nerve does not usually cause a complete loss of sensation in its dermatome, although an alteration in sensation may be found.

Shingles is a painful skin rash caused by infection of nerves within one or more dermatomes with a virus. The red rash appears within the affected dermatomes.

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Myotomes are groups of muscles innervated by a single spinal nerve.

The table shows that, unlike the dermatomes, each spinal nerve innervates muscles in one section of the limb - focused around the joint that is being moved.

Proximal muscles in the upper limb are innervated by upper segments of the cervical cord , and distal muscles by lower segments (via the brachial plexus); the same is true of the lower limb and the lumbar cord and the lumbosacral plexus.

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