Questions: - Review what is the main activity of all muscles - Know how cardiac muscle differs from skeletal muscle

The main activity of all muscles is contraction. Muscles contract to produce movement, maintain posture, and generate heat.

Cardiac muscle differs from skeletal muscle in several ways:

1. Location: Cardiac muscle is found only in the heart, while skeletal muscle is attached to bones and is responsible for voluntary movements.
2. Control: Cardiac muscle is involuntary, meaning it contracts without conscious control, whereas skeletal muscle is voluntary and controlled consciously.
3. Structure: Cardiac muscle cells are branched and interconnected, allowing for synchronized contractions, while skeletal muscle cells are long, cylindrical, and multinucleated.
4. Function: Cardiac muscle is specialized for continuous, rhythmic contractions to pump blood, while skeletal muscle is designed for quick, forceful contractions to move the body.

In summary, the main activity of all muscles is contraction, and cardiac muscle differs from skeletal muscle in terms of location, control, structure, and function.