Muscular System

Muscular System

1. 10.1 Overview of Muscular Tissue

   • 1. There are three types of muscular tissue are skeletal, cardiac, and smooth. Skeletal muscle tissue is primarily attache to bones; it is striated and voluntary. Cardiac muscle tissue forms the wall of the heart; it is striated and involuntary. Smooth muscle tissue is located primarily in internal organs; it is nonstriated (smooth) and involuntary.
     • 2. Through contraction and relaxation, muscular tissue performs four important functions: producing body movements, stabilizing body position, moving substances within the body and regulating organ volume, and generating heat.
       • 3. Four special properties of muscular tissues are (1) electrical excitability, the property of responding to stimuli by producing action potentials; (2) contractility, the ability to generate tension to do work; (3) extensibility, the ability to extend (stretched); and (4) elasticity, the ability to return to original shape after contraction or extension.

2. 10.2 Structure of Skeletal Muscle Tissue

   • 1. The subcutaneous layer separates skin from muscles, provides a pathway for blood vessels and nerves to enter and exit muscles, and protects muscles from physical trauma. Fascia lines the body wall and limbs that surround and support muscles, allows free movement of muscles, carries nerves and blood vessels, and fills space between muscles
     • 2. Tendons and aponeuroses are extensions of connective tissue beyond muscle fibers that attach the muscle to bone or to other muscle. A tendon is generally ropelike in shape; an aponeurosis is wide and flat
       • 3. Skeletal muscles are well supplied with nerves and blood vessels. Generally, an artery and one or two veins accompany each nerve that penetrates a skeletal muslce
         • 4. Somatic motor neurons provide the nerve impulses that stimulate skeletal muscle to contract
           • 5. Blood capiilaries bring in oxygen and nutrients and remove heat and waste products of muscle metabolism
             • 6. The major cells of skeletal muscle tissue are termed skeletal muscle fibers. Each muscle fiber has 100 or more nuclei because it arises from the fusion of many myoblasts. Satellite cells are myoblasts that persist after birth. The sarcolemma is a muscle fiber's plasma membrane; it surrounds the sarcoplasm. Transverse tubules are invaginations of the sarcolemma.
               • 7. Each muscle fiber (cell) contains hundreds of myofibrils, the contractile elements of skeletal muscle. Sarcoplasmic reticulum (SR) surrounds each myofibril. Within a myofibril are thin and thick filaments, arranged in compartments called sarcomeres
                 • 8. The overlapping of thick and thin filaments produces striations. Darker A bands alternate with lighter I bands.
                   • 9. Myofibrils are composed of three types of proteins: contractile, regulatory, and structural. The contractile proteins are myosin (thick filament) and actin (thin filament). Regulatory proteins are tropomyosin and troponin, both of which are part of the thin filament. Structural proteins include titin (links Z disc to M line and stabilizes thick filament)