What must a muscle cell do to keep contracting?

A muscle cell must keep contracting by maintaining a constant supply of:

1. Calcium ions (Ca2+): Ca2+ ions are essential for muscle contraction to occur. They bind to troponin, causing a conformational change that allows myosin to bind to actin and form cross-bridges. This process repeats itself for as long as there are Ca2+ ions available.

2. Energy: Adenosine triphosphate (ATP) is the energy source for muscle contraction. ATP is broken down into adenosine diphosphate (ADP) and inorganic phosphate (Pi), releasing energy that is used to power the formation, dissociation, and reforming of the cross-bridges between myosin and actin filaments.

3. Oxygen and Nutrients: Muscle cells require a constant supply of oxygen and nutrients, such as glucose, to generate ATP through cellular respiration. Without oxygen and nutrients, the muscle cell will eventually fatigue and be unable to sustain contraction.