The Muscular System 36-2

1. The Muscular System36-2 BIO 1004 Flora

2. Types of Muscle Tissue • 3 Different Types of muscle tissue: • Skeletal • Smooth • Cardiac • Each type of muscle is specialized for a specific function

3. Skeletal Muscle • Usually attached to bones • Responsible for voluntary movements • Have alternating light bands and dark bands • This is the reason for the name “striated” muscle • Large and vary in length • 1-30 cm • Muscle cells are called muscle fibers • Consist of fibers, connective tissues, blood vessels, and nerves

4. Smooth Muscle • Not under voluntary control • Spindle shaped, one nucleus, and not striated • Found in stomach, intestines, and blood vessels • Forms digestive tract and controls the blood flow through circulatory system • Most can function without the CNS • Connected through “gap junctions” that allow muscle cells to communicate with each other.

5. Cardiac Muscle • Found in the heart • Much like a combination of skeletal and smooth muscle • Striated, but smaller cells than skeletal • One or two nuclei • Under control of the CNS

6. Muscle Contraction • Muscle fibers in skeletal muscle are composed of small structures called myofibrils • Striations in skeletal muscle and cardiac muscle is composed of protein filaments called actin and myosin • Filaments are arranged in clusters called “sarcomeres” • Sarcomeres are separated from each other by “z-lines”

7. Myofibril

8. Muscle Contraction Cont. • Actin and myosin are responsible for muscle contraction • Muscles contract when the thin filaments in the muscle fiber slide over the thick filaments • Myosin must form a “cross-bridge” with actin filament • As the cross-bridge changes shape, it pulls on the actin filament which decreases the distance between z-lines • When thousands of myosin bridges change shape, the muscle fiber shortens and the muscle contracts

9. Muscle Contraction Cont. • Muscle contraction energy is supplied by ATP • Controlled by the CNS – motor neurons connect to muscle cells • The point at which the motor neuron comes in contact with the muscle cell is known as the neuromuscular junction • The neurotransmitter involved in muscle contraction is acetylcholine • Muscle cells remain contracted until the release of acetylcholine stops • Max contraction vs. weak contraction • Few cells vs. all muscle cells

10. Interaction Between Muscles and Bones • Skeletal muscles are joined to bone by connective tissue called tendons