Muscle Development - Anatomy & Physiology

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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

1. Prescursor cells migrate from the dermomyotome.
   • They are mesenchymal
   • Divide rapidly en route and are undifferentiated.
2. Cells differentiate to form myoblasts.
   • Cells still mesenchymal but can no longer migrate as differentiated.
   • Muscle gene expression.
3. The myotube is formed; cells become multi - nucleated to form a syncytium.
   • Muscle enzymes are produced.
4. The myofibre is produced.
   • Contractile proteins are present.

Limb Muscle Development

• Skeletal muscle of the limbs originates from those somites closest to the limbs.

1. Signalling factors from the limbs cause cells to migrate from the somite.
   • Singalling factors cause the hypaxial lamina to break down.
   • This allows cells to migrate.
   • Few cells migrate; but they rapidly prolifate during migration to increase cell numbers.
2. 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.
3. Cells continue migration within these populations.
4. Once cells have reached their destinations, they differentiate.