• Document: Chapter 7 The Muscular System. Most abundant tissue (600+)
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Chapter 7 The Muscular System Most abundant tissue (600+) I. Characteristics of Skeletal Muscle 1) Function: motion; posture; body heat – Excitable, Contract/Extend, Elastic 2) Structure A. Connective tissue: – Epimysium (fascia): wraps whole muscle – Perimysium: wrap fasciculi (bundle of cells) – Endomysium: wrap muscle cell (fiber) B. Muscle Cell/Fiber: a) Sarcolemma (cell membrane): long striated cylinder w/nuclei • T (transverse) tubules: wrap sarcolemma & connect (pass message-Action Potential) to Sacroplasmic Reticulum: Hi Ca++ conc (conduct (AP) to actin) b) Sarcoplasm: cytoplasm w/2 myofibril types 1) Actin: thin, beaded – Troponin: Ca-binding sites – Tropomyosin: regulates myosin binding sites (block w/no AP) 2) Myosin: thick, golf clubs, binds/moves actin Sarcolemma: C) Sarcomere: basic repeating myofibril units 1) Z disk: anchors actin; divides sarcomeres 2) I band: light zone: actin only; spans Z disk 3) A band: dark zone; length of myosin (w/actin) 4) H Zone: myosin only; middle 5) M line: anchors myosin; center 3) Nerve/Muscle Membrane Potential (polarized): sends message for action Resting: + out (Na+, K+ leak/- in (protns-) Depolarization: AP-charge reversd; Na+ in Repolarization: K+ out Na/K pump returns resting potential 4) Nerve Supply Motor Neurons to Muscles Motor Motor Unit: – 1 neuron to all muscle fibers – Many units per muscle  Neuromuscular Junction or synapse 1. AP to presynaptic terminal (Ca++ in) 2. Acetylcholine (Ach): neurotransmitter crosses synaptic cleft (space) open Na+ channels 3. Depolarization (postsyn) muscle fiber sarcolemma Na channel closed without Ach Na channel opened with Ach Acetylcholinesterase: brkdwn Ach Myasthenia Gravis: antibodies destroy Ach receptors (weakness) Curare binds ACH receptors–flaccid paralysis 5) Muscle Contraction Sliding Filament Mechanism: – Myosin cross-bridges pull actin toward H zone – H/I shorten/A unchanged 1. AP from nerve to muscle 2. Ach released; Na channels open 3. Na in; AP->sarcolemma->T tubls->s. reticlm 4. S. reticulum releases Ca to actin troponin 5. W/Ca++ Tropomyosin exposes binding sites 6. Myosin form cross-bridge w/actin (rigor) 7. Power stroke moves actin w/ADP+P release 8. Cross-bridge broken/head rests w/2ND ATP • Rigor Mortis: No ATP avail for release w/death 9. Contraction continues w/Ca and ATP 1. ACH released 2. AP moves along membrane and T-tubules 3. Ca released from SR voltage gated Ca channel opens 4. Ca binds to Troponin-C conformation changes favor tropomyosin opens actin sites 5. myosin cross-bridges attach- detach from actins/pulls filament toward M-line 6. Ca removed (uptake by SR) 7. tropomyosin blocks actin sites relaxation 6) All-or-none contraction: all fibers fully Motor Unit All the muscle fibers (cells) innervated by the same motor neuron All-or-None Principle: All muscle fibers that make up a motor unit contract fully together. This principle holds true at the sarcomere, myofibril, and muscle fiber levels as well. Partial contraction occurs at the muscle level because all motor units are not contracting at the same time. Recruitment: The process by which the number of actively contracting motor units is increased. 7) Summation: increased contraction force w/↑ stimulation=tetanus: sustained contractn (no relax) Fused or Complete Tetanus: A sustained maximum contraction in which individual contractions are not discernable. In fused tetanus, multiple stimuli are occurring so fast, the muscle does not undergo any relaxation. 8) Recruitment:↑ units over time = smooth strength 9) Energy Requirements: • Aerobic Resp: Glucose + O2 = ↑ ATP • Anaerobic Resp: Glucose = ATP + lactic acid – ATP↓/Creatine P↑: rapidly converted to ATP Food source Creatine level;grams/pound Herring 3.0/lb Pork 2.3/lb Salmon 2.0/lb Beef 2.0/lb Tuna 1.8/lb Cod 1.4/lb Cranberries .0009/lb 10) Types of Muscle Contractions: a) Isometric: no shortg w/↑ tensn: posture b) Isotonic: constant tensn w/shortg: movemt • Concentric (tension ↑ w/shortening) • Eccentric (constant tensn w/lengthenin-lower wght) 11) Myofibril Types: a) Sl

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