Mr Brannon Thought you might enjoy a few colorful muscle slides

Figure 8.2. Exercise Physiology, 4 th Ed. SK Powers & ET Howley. McGraw-Hill 2001.

Summary: Early steps in skeletal muscle development Portion of dorsal mesoderm Divides into tissue blocks (somites) Activin B Portion of somitic mesoderm committed to form muscle MyoD Myf-5 Myogenin Myf-6 Proliferation of myoblasts Activin B FGFs TGF-B Immediate early genes (fos, myc, jun) Differentiation and fusion to form myotubes MyoD Myf-5 Myogenin Myf-6 Maturation to myofibers Muscle assembly and fiber type determination

I IIa IIx

Type I fibers = red Type II fibers = white Capillaries appear as black dots around fibers Capillary supply is highest in type I myofibers

Mixture of small (atrophied) fibers and large (hypertrophied) fibers. The small ones are dying and the enlarged ones are compensating. Comparison of normal vs. diseased muscle Normal healthy sample Muscle fibers are similar in size Diseased Copper = type I muscle fibers Green = type IIa muscle fibers Black = type IIx muscle fibers

Satellite cells are key players in growth and repair of muscle fibers Satellite cell outside of muscle fiber Satellite cells isolated from muscle in cell culture

Satellite cells fuse together during development and repair

Myostatin is a negative regulator of muscle mass and it is important during development to ensure that muscle develops normally. This is what happens when the anti-growth factor myostatin fails (genetic mutation) Belgian Blue7 mo. male

I had to include my favorite cartoon…