1. Muscle Physiology Anatomy & Physiology/Tissues, Bones and Muscles

2. Muscle Functions Muscles have four major roles in our bodies: 1. Produce movement 2. Maintain posture 3. Stabilize joints 4. Generate heat: a by-product of muscle activity

3. Anatomy of a Muscle To understand how muscles move, it is essential to understand their basic anatomy. The outermost layer of a muscle is called the epimysium, which is a very tough connective tissue Epimysium

4. Muscle Anatomy Continued… Below the epimysium is another layer of connective tissue called the perimysium, which covers bundles of muscle cells called a fascicle. Epimysium Perimysium Fascicle

5. Anatomy of a Muscle Continued… Each muscle fiber in the fascicle is wrapped by a thin connective tissue called an endomysium. Epimysium Perimysium Fascicle Endomysium

6. Muscle Fibers Successful muscle movement (contraction or relaxation of a muscle) depends on a very organized coordination of many parts of the muscle. A single muscle cell is often called a muscle fiber, because it is long and contains multiple nuclei.

7. Myofibrils A single muscle fiber is made of many myofibril organelles.

8. Actin and Myosin Filaments Each myofibril is made of a combination of actin filaments, which are thin, and myosin filaments, which are thick. The actin and myosin are arranged in repeating units called sarcomeres.

9. Parts of the Sarcomere Each area of the sarcomere has a specific name, because these units are essential for understanding how muscles contract and relax: Thin (actin) filaments are attached to membranes called Z discs (or Z lines). A full sarcomere extends from one Z disc to another. A bands contain both thin (actin) and thick (myosin) filaments. I bands contain only thin (actin) filaments and span parts of two sarcomeres. Alternating light (I) and dark (A) bands give the myofibril a striped appearance. The H zone contains only thick (myosin) filaments.

12. Muscle Movement When muscles contract (shorten) the Z discs move closer together. This means that the H zone becomes smaller and the the I bands shorten. When muscle relax (lengthen), the Z discs move apart. The means that the H zone becomes larger and the I bands get longer.

13. Muscle Movement Continued… The movement of sarcomeres is controlled by crossbands that connect actin and myosin. These crossbands attach the myosin and actin filaments and use ATP as a source of energy to slide the filaments across each other. This model of muscle movement is known as the Sliding Filament Theory. http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter42/animations.html#

15. Prentice Hall Muscle Contraction Video 4 minutes http://www.youtube.com/watch?v=83yNoEJyP6g