[Histogenesis, degeneration, regeneration and adaptation, aging and compensation in the skeletal muscles]

The concept of multicellular histogenesis of skeletal muscle fibre is the basis for understanding embryonal genesis of the voluntary muscles as well as muscle fibre regeneration. Formation and maintenance of the neuromuscular units are preconditions for function. Embryonic development and histogenesis regeneration are described. Changes resulting from metabolic defects, trauma, neurogenic and muscular disease are contrasted. Changes in nerves and synaptic junctions due to degeneration and regeneration are illustrated. Alteration in fibre type composition and muscle fibre diameter are regarded as the principle form of muscle adaptation to a changed loads. A central nervous system mechanism influencing fibre type and a peripheral humoral mechanism influencing the magnitude of peripheral motor units are postulated. The role of intramuscular sprouting is underlined. The structurally recognizable correlates of aging, such as decreased fibre diameter, increasing fibre type grouping and reduction of the total number of muscles fibres should be viewed as physiological phenomena. Sensomotor regulation of compensatory mechanism of muscular activity including fibre type grouping, compensatory hypertrophy, target fibres and ring fibres results in distinctive patterns under etiologically distinct pathological conditions.