The muscular system is the body system that produces movement, supports posture, and helps protect internal organs. More than 600 skeletal muscles work with bones and joints so the body can walk, lift, breathe, speak, and make facial expressions. Muscles also help maintain body temperature because contracting muscle fibers release heat.
Understanding this system helps explain athletic performance, injuries, fatigue, and everyday body movements.
Key Facts
- Skeletal muscles pull on bones through tendons to create movement at joints.
- Muscles contract when actin and myosin filaments slide past each other inside muscle fibers.
- The main muscle types are skeletal, cardiac, and smooth muscle.
- Force increases when more motor units are recruited by the nervous system.
- Power = work / time, so faster muscle work produces greater power if the work is the same.
- ATP provides the direct energy for muscle contraction and must be continually regenerated.
Vocabulary
- Skeletal muscle
- A voluntary muscle attached to bones that produces body movement and helps maintain posture.
- Tendon
- A strong band of connective tissue that attaches muscle to bone.
- Muscle fiber
- A long muscle cell that contains protein filaments specialized for contraction.
- Motor unit
- A motor neuron and all the muscle fibers it controls.
- Antagonistic pair
- Two muscles or muscle groups that produce opposite actions at a joint, such as the biceps and triceps.
Common Mistakes to Avoid
- Thinking muscles push bones, because skeletal muscles can only pull when they contract, so movement usually requires muscles arranged in opposing pairs.
- Confusing tendons with ligaments, because tendons attach muscle to bone while ligaments attach bone to bone at joints.
- Assuming bigger muscles always mean more strength, because strength also depends on nervous system recruitment, fiber type, training, leverage, and tendon attachment.
- Ignoring recovery after exercise, because muscle tissue needs time, nutrients, and rest to repair microscopic damage and restore energy stores.
Practice Questions
- 1 A student lifts a 20 N backpack upward by 1.5 m. How much work is done on the backpack?
- 2 During a curl, a muscle does 60 J of work in 3 s. What is the average power output?
- 3 Explain why bending and straightening the elbow requires both the biceps and triceps rather than only one muscle.