MUSCLES copy - MUSCLES Muscle Functions (6): Supply force...

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MUSCLES Muscle Functions (6): Supply force for movement and together with the skeletal system, they allow an animal to act Restrain movement, by keeping the body in place Surround visceral organs, blood vessels, respiratory channels, and glands and influence their activities Form sphincters that control the passage of material through tubular structures Produce heat for thermoregulation (shivering) Produce electrical energy Muscles Types (3): 1. Skeletal 2. Cardiac 3. Smooth Muscle Structure: Skeletal (striated, voluntary) o 40% of body mass o Myotomes of embryo o Myoblast end to end fusion o Bundles of fibers, connective tissue, blood vessels, and nerves o Wrapped in connective tissue sheath o Cells = largest of body, extend length of muscle, called muscle fibers (membrane = sarcolemma, cytoplasm = sacroplasm) Composed of myofibrils Multinucleated Actin and myosin o Sacromeres (A band, H zone, M line, I band) Sarcoplasmic reticulum Surrounded by T-tubules (transverse tubules) Neuromuscular junctions connect to nervous system Motor end plate Cardiac (striated, involuntary) o Heart only o Single branching nucleus, elongated fibers o Intercalated disk connect o Involuntary contraction Autorhythmic cell electrical impulses o Embryonically – Hypomere
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Smooth (smooth, involuntary) o Spindle-shaped, single nucleus o Surround organs, blood vessels, muscles, etc o Involuntary, slow contraction Autonomic nervous system, hormones o Splanchnic mesoderm mesenchyme cells splanchnopleure Muscle Movement (Skeletal): Contraction o Tendons Aponeuroses = origin/insertion o Fibers = >1000 myofibrils Proteins: actin/myosin (contractile), tropomyosin/troponin (regulatory), titin/ nebulin (accessory) Myosin = thick filament – clustered, hinge-like heads – swivel Actin = thin filament – (G-actin), myosin head binding site / (F-actin) – twist to form thin o Sliding Filament Theory (5 steps) Myosin = motor motion energy, 45 ° heads, no actin ATP ADP and P, cocked 90 ° heads (cross bridge) No P, 45 ° heads = power stroke Myosin no ADP, actin bonded = rigor state Repeat actin to M line, shortening o Isotonic contraction = shorten, pull together o Isometric contraction = held by forces o Negative work contraction = lengthen, tension Antagonistic force (groups) o Relaxation = resting length o Synergistic action – modify muscle actions Properties: tonic and phasic o Tonic – slow, low force, not tired, multiple end plates Grade = nerve action frequency o Phasic (twitch) – single end plate, action potential, fast Grade = All-or-None, number active motor units 2 categories: fast and slow phasic fibers Slow fibers – oxidative metabolism, blood vessel rich + mitochondria and myoglobin “red muscle” o Slow (wait for oxygen), isometric/slow repetitive isotonic Fast fibers – rapid movements, oxidative and anaerobic glycolysis
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This note was uploaded on 04/29/2010 for the course BIOL 1404 taught by Professor Machaeldini during the Fall '09 term at Texas Tech.

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MUSCLES copy - MUSCLES Muscle Functions (6): Supply force...

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