Page 111 - 84 human physiolofy part-1

The Muscular System

Sliding Filament theory

When a muscle contracts, the actin is pulled along myosin toward the center of the sarcomere until
the actin and myosin filaments are completely overlapped. The H zone becomes smaller and smaller
due to the increasing overlap of actin and myosin filaments, and the muscle shortens. Thus when the
muscle is fully contracted, the H zone is no longer visible (as in the bottom diagram, left). Note that the
actin and myosin filaments themselves do not change length, but instead slide past each other.

Sliding myofibril (GFDL - Slashme)
Cellular Action of Skeletal Muscles

During cellular respiration the mitochondria, within skeletal muscle cells, convert glucose from the
blood to carbon dioxide and water in the process of producing ATP (see cell physiology). ATP is
needed for all muscular movement. When the need of ATP in the muscle is higher than the cells can
produce with aerobic respiration, the cells will produce extra ATP in a process called anaerobic
respiration. The first step of aerobic respiration(glycolysis) produces two ATP per glucose molecule.
When the rest of the aerobic respiration pathway is occupied the pyruvate molecule can be converted to
lactic acid. This method produces much less ATP than the aerobic method, but it does it faster and
allows the muscles to do a bit more than if they relied solely on ATP production from aerobic

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