Aging of the neuromuscular apparatus.

With age marked changes in metabolism and function of muscle fibers appear: electroexcitability thresholds rise, critical polarization level and membrane resistance decrease, time of action potential increases and its amplitude decreases, lability is reduced. The level of intracellular sodium increases and that of potassium decreases. Shifts in ionic asymmetry of muscle fibers are connected with changes in their membrane permeability and a modified function of the sodium-potassium pump. Along with the impairment of nervous influences on muscle fibers in old age, their sensitivity to many hormonal factors increases. Loading levels all age differences in the regulation of skeletal muscle vascular tone. The relationships between the activity of the genetic apparatus and electrical properties of the cell are altered.