Abstract
The muscles of an individual vary in their morphological and contractile properties and in their patterns of innervation. At one time, it was thought that a fairly homogeneous population of myoblasts gave rise to myotubes that were subsequently instructed to diversify by various extramuscular factors. There is now, however, considerable evidence that myoblasts are heterogeneous, and that heritable differences among them interact with environmental influences to give each muscle its distinct characteristics.
