The muscular system is the body system responsible for movement. The muscles are attached to bones and make up important organs, like the heart, digestive organs and blood vessels.

Explore antagonistic muscles. Learn the definition of an antagonist muscle and understand how it differs from an agonist muscle. See examples of...

Learn about antagonistic muscles in our engaging video. Learn how these muscles work in pairs to create movement and stability in the body, followed by a quiz.

Learn what the iris of the eye is, its definition, and various functions. Discover the purpose of the human iris and what the iris does.

Understand the physiology of erection and ejaculation by understanding their main differences. Learn what nerves control erectile function and trigger ejaculation.

See an arm muscle diagram to learn about arm muscle anatomy. Explore the parts of arm muscle and discover the purpose and function of each part.

Learn the difference between agonist and antagonist muscles in this 5-minute video lesson. Understand how contractions work and test your knowledge with a quiz.

In this lesson, learn about arm anatomy. Understand arm muscle names and groups, including the upper arm muscles and the forearm muscles.

Actin and Myosin in Muscle Contraction So, how do muscles contract? The functional units of muscle fibers are called sarcomeres. When viewed under the microscope skeletal muscle has a striped pattern.

In this lesson you will find basic background on the muscle system and skeletal system as well as how they work collaboratively to perform the important function of human movement.