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Unformatted text preview: Ch. 12 Muscle Physiology I) Skeletal Muscle Structure a) With few exceptions, skeletal muscles are connected to at least 2 bones; muscles are connected to bones via tendons b) Structure at the Cellular Level i) The part of the muscle that generates force is the body ; it contains many bundes (aka fascicles ) of individual muscle cells, as well as connective tissue, blood vessels, and nerves ii) Each fascicle contains hundreds of thousands of muscle cells, called fibers because of their elongated shape iii) Muscle cells have MANY NUCLEI because each is formed during embryonic life from the fusion of many cells iv) These nuclei lie immediately below the fiber’s plasma membrane, called the sarcolemma v) The sarcoplasm (cytoplasm) is packed with mitochondria and hundreds of banded, rodlike elements called myofribrils (a bundle of overlapping thick and thin filaments made of myosin and actin) vi) A saclike membranous network called the sarcoplasmic reticulum surrounds each of the myofibrils and is closely associated with transverse tubules , which are connected to the sarcolemma and penetrate into the cell’s inerior vii) The sarc retic stores calcium ions and then releases them into the cytosol when a muscle cell is stimulated to contract c) Structure at the Molecular Level i) Skeletal muscle cells have a striped appearance, called striated ii) Myofribirls composed of a fundamental unit called a sarcomere that repeats over and over; each sarcomere is bordered on either end by Z lines which run perpendicular to the long axis and anchor the thin filaments on one end; the thick filaments are connected by M lines (1) A band – region spanning the length of the filaments (2) H zone – lighter region in the center, absence of thin filaments (3) I band – brightest region, occupies space between A band and adjacent sarc.; no thick filaments iii) Thin and thick filaments made up of actin and myosin, called contractile proteins (1) Thin filaments are actin monomers (called G actin because they are globular proteins), each of which has a myosin binding site; G actins linked together end to end to form strands called F actin (fibrous); two F actins arranged in a double helix to form the actin strands in a thin filament (a) Also present are two special proteins called regulatory proteins (i) Tropomyosin – long fibrous molecule that blocks the myosin binding sites in muscles at rest (ii) Troponin – complex of three proteins, one that attaches to actin strandm one that binds to tropomyosin, one containing a site which calcium ions can bind to reversibly (b) Each thick filament is made of hundreds of myosin molecules (each looks like...
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This note was uploaded on 04/07/2008 for the course APK 2105 taught by Professor Brooks during the Spring '07 term at University of Florida.
- Spring '07