Muscle Types, Functions, and Microscopic Anatomy Pg. 162 – 167

1. Muscle Types, Functions, and Microscopic AnatomyPg. 162 – 167 October 2, 2012

2. Overall Function of Muscles • Contraction, a.k.a. shortening • A unique characteristic that sets it apart from any other body tissue • Muscles are responsible for basically all body movement and can be viewed as the “machines” of the body.

3. Muscle Structure • Muscles are a tissue made up of many muscle cells • All muscle cells are elongated and are called muscle fibers • Muscle cells, or fibers, are made up of myofilaments • Myofilaments allow a muscle to contract

4. Muscle Types – Skeletal Muscle • Location: covers the skeleton • Multinucleate • Largest of the muscle fiber types • Striated muscle – fibers appear to be striped • Voluntary • Often activated by reflexes as well • Contracts rapidly with great force, but tires rapidly

5. Muscle Types – Skeletal Muscle • Bundled in several sets of connective tissue • Endomysium surrounds each muscle fiber (cell) • Perimysium surrounds bundles of fibers (cells) called fascicles • Epimysium surrounds a bundle of fascicles (the whole muscle) • Tendons • Anchor muscle to bone and provides durability

6. Muscle Types – Smooth Muscle • Location: lining of hollow organs • Uninucleate • No striations • Involuntary • Propels substances along a pathway through the body • Arranged in sheets or layers – usually two, one running lengthwise and one circling the outside • Contraction is slow and sustained

7. Muscle Types – Cardiac Muscle • Location: heart ONLY • Serves as a pump that propels blood around the body • Uninucleate • Striated • Involuntary • Cardiac muscle cells are connected by intercalated disks, which allow free movement of substances between cells

8. Muscle Functions • Producing movement • Muscles allow us to move, respond, express emotions, pump blood, move substances through body organs • Maintaining posture • Skeletal muscles can hold us upright despite gravity • Stabilizing joints • Tendons help reinforce and stabilize joints, especially those that are articulated poorly • Generating heat • A by-product of muscle activity – body temperature is 37˚C or 98.6˚F.

9. Microscopic Anatomy of Skeletal Muscle • Each muscle fiber (cell) is made up of many myofibrils • Myofibrils are made up of units called sarcomeres • Each sarcomere includes myofilaments called actin and myosin • Actin = thin filament • Myosine = thick filament • The myofilaments are arranged in light (I) and dark (A) bands – this is what gives the muscle is striped, or striated, appearance • Light (I) bands have a Z disc • Dark (A) bands have an H zone