Muscle Development - Anatomy & Physiology
Introduction
Muscle cells can come from two lineages in the somite. Limb and body muscle develop from hypaxial muscle in the lateral regions of the somite. Back muscle develops from epaxial muscle in the dorsal regions of the somite. Muscle fibres have hundreds of nuclei and function as a syncytium.
Muscle Cell Differentiation
Precursor mesenchymal cells migrate from the dermomyotome. They divide rapidly en route and are undifferentiated. The cells with muscle gene expression differentiate to form myoblasts, they are still mesenchymal cells, but can no longer migrate as they are differentiated. The myotube is formed and cells become multi - nucleated to form a syncytium. Muscle enzymes and the myofibre is produced. Contractile proteins are present.
Limb Muscle Development
Skeletal muscle of the limbs originates from those somites closest to the limbs. Signalling factors from the limbs cause cells to migrate from the somite and causes the hypaxial lamina to break down, allowing cells to migrate. Few cells migrate but they rapidly proliferate during migration to increase cell numbers. Muscle precursors migrate into the limb bud (proliferating). At the proximal region of the limb, two populations of cells exists, these are the dorsal and ventral masses. Cells continue migration within these populations. Once cells have reached their destinations, they differentiate.