Altered Physiology and Diseases of the Muscles

The skeletal muscles or flesh are essential for the motor functions as well as the shape and features of our body. The muscular atrophy (shrinkage of muscle mass) may lead to a variety of diseases of the muscles. These diseases are distinguished with respect o the site of origin of a disorder as mentioned below:

1. Origin in motor neurons: Polymyelitis, progressive muscular atrophy

2. Origin in the nerve fibers: Polyneuritis

3. Origin in the myoneural junction: Myasthenia gravis, myotonia congenital, and

4. Origin in the muscle only: Primary muscular dystrophy.

All voluntary muscle have innervation by motor neurons. The muscle fibers are composed of myofibrils and these fibrils appear to be the ultimate functional units of the muscle and have alternate light and dark bands. The contractile protein of the muscle is called actomycin (AM) and is composed of actin and myosin. The actomycin is considered to be the structural protein of the resting myofibrils and contain many enzymes necessary the muscle metabolism. The organic phosphate compound called adenosine triphosphate (ATP) is an energy rich compound and is attached to actomycin of myofibrils. The neuronal spark of the motor neurons fires the adenosine triphosphate-actomycin linkage and breaks it. The adenosine triphosphate (ATP) is liberated and its breakdown provides energy for the muscle contraction. During contraction of the muscle, the actin threads could be shortened to 40% of its original relaxed phase size. The physiology of muscle contraction involves a series of molecular interactions and rearrangements within the complex structure of actin, myosin, and adenosine triphosphate.

The change in the functions of any part of the above cited metabolic pathway may lead muscle weakness. The microscopic examination of muscle biopsy may help to achieve a proper diagnosis. There muscle biopsy could reveal an involvement of a whole bundle of muscle fibers in the cases with neurogenic origin. I cases affected by primary muscular dystrophy only some the fibrils may be involved. The ultrastructural study of the muscle biopsy by a transmission electron microscope is always helpful in achieving an accurate diagnosis of the diseases of the muscles.