Chapter 70. Dermatome and Cutaneous Innervation of The Limbs - Review of Medical Embryology Book

Dermatome distribution and cutaneous innervation are related to the growth and rotation of the limbs

A DERMATOME is an area of skin (sensory) supplied by a single spinal nerve and its dorsal root ganglion

Peripheral spinal nerves grow from the brachial plexi into the upper limb buds, and lumbosacral plexi grow into the lower limb buds, during week 5
The spinal nerves (dermatome nerves) are distributed in segmental bands to supply the dorsal and ventral surfaces of the limb buds

As the bud elongates, the cutaneous nerves migrate out along the limbs, and although the original dermatomal patterns change with growth, there is still an orderly sequence of nerve distribution
The limb dermatomes can be traced down the lateral side of the arm and up its medial side, while those of the lower limb can be traced down the ventral side and up the dorsal side
Autonomic nerves that supply the blood vessels grow out into the limb buds with the spinal nerves

A CUTANEOUS NERVE supplies an area of the skin that is related to a peripheral nerve. Note that any cutaneous nerve may contain fibers from several individual spinal nerves. Therefore, cutaneous nerve areas and dermatome areas show much overlapping. A cutaneous nerve area is generally broader and wider than an area supplied by only a single spinal (dermatome) nerve