MUSCLE CHEMISTRY

Living muscles are like laboratories where quick, chemical reactions make energy. Mitochondria, which are microscopic structures inside cells, produce the chemical adenosine triphosphate (ATP). ATP is the major
chemical that produces the energy muscles need to move. However, muscle fibers only have a small amount of available ATP. They must get ATP more to keep moving.

This is the molecular structure of ATP. The human body stores and uses ATP to create the energy

needed for everyday life-sustaining activities.

When muscles use up stored ATP, the body breathes harder to take

in more oxygen. The heart pumps faster to send more oxygenated blood

to muscle cells to make more ATP. Increased oxygen in the blood stimulates

the liver to convert glucose sugars from nutrients in food. The liver

then releases the glucose into muscle cells, which builds up the ATP levels.

With more ATP, thick myofilaments can detach themselves from thin myofilaments

so that they can move.

Another chemical reaction begins when electrical signals from the

brain cause the release of acetylcholine. This neurotransmitter triggers

electrical activity in muscle cells. The cells release stored calcium ions.

In turn, calcium makes it possible for thin and thick muscle filaments to

slide past each other. When that happens, muscles move.