Science · Support & movement
Muscles and Contraction
Estimated time includes reading and one quiz. Take the time you need.
Start here: key ideas
- Skeletal, cardiac, and smooth muscle have different locations and controls.
- A sarcomere shortens when actin slides past myosin.
- Calcium exposes binding sites, and ATP powers cross-bridge cycling.
- Motor units and opposing muscles control force and movement.
What you’ll be able to do
- Compare the three muscle tissue types.
- Explain how a sarcomere contracts.
- Connect motor units and opposing muscles to movement.
Follow a muscle signal from the motor neuron to force and relaxation.
Optional review
If you’d like to review the basics, visit Skeleton and Bone Structure, Joints and Movement. You can start this lesson without completing those first.
Three tissues, three control patterns
Skeletal muscle attaches to bones, is striated, and is usually under voluntary control. Cardiac muscle forms the heart, is striated, and contracts without conscious control. Its branched cells connect through intercalated discs. Smooth muscle is in hollow organs and vessels. It lacks visible striations and moves materials or changes tube width automatically.
Structure fits each job. Skeletal fibers can produce quick, directed movement. Cardiac cells connect electrically so the heart contracts as a coordinated pump. Smooth muscle contracts more slowly and can maintain pressure or move material for long periods, as in blood vessels and intestines.
From whole muscle to fibers
Read from large to small: whole muscle → bundles → muscle cells (fibers) → myofibrils → repeating units called sarcomeres. The extra labels for tissue coverings help locate parts; they are not a required name list.
From whole muscle to fibers — OpenStax College, Anatomy & Physiology (2014 CC BY archive). CC BY 3.0. Original source image reproduced unchanged; explanatory caption added.
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