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Chapter 9 Muscular System Three Types of Muscle Tissues Cardiac Muscle Skeletal Muscle • • • • • • Smooth Muscle • • • 9-2 Structure of a Skeletal Muscle Skeletal Muscle • organ of the muscular system • skeletal muscle tissue • nervous tissue • blood • connective tissues • fascia • tendon 9-3 Structure of a Skeletal Muscle • • • • • muscle • fascicles • muscle fibers • myofibrils • thick and thin filaments 9-4 Skeletal Muscle Fiber • sarcolemma • sacroplasm • • • triad • cisterna of sarcoplasmic reticulum • transverse tubule • myofibril • • • sarcomere 9-5 Sarcomere • I band • A band • H zone • Z line • M line 9-6 Myofilaments Thick Filaments • • Thin Filaments • • associated with troponin and tropomyosin Muscle 3.mov 9-7 Neuromuscular Junction • site where axon and muscle fiber communicate • • motor end plate • • synaptic vesicles • 9-8 Motor Unit • • 9-9 Stimulus for Contraction • acetylcholine (ACh) • • binds to acetylcholine receptors on motor end plate • • Muscle 2.mov 9-10 Excitation Contraction Coupling • • • position of tropomyosin is altered • • 9-11 Sliding Filament Theory • When sarcromeres shorten, thick and thin filaments slide past one another • • 9-12 Cross-bridge Cycling • • myosin crossbridge pulls actin •ADP and phosphate released from myosin • • linkage between actin and myosin cross-bridge break •ATP splits • Muscle 4.mov 0010.exe 9-13 Relaxation • acetylcholinesterase – • • Muscle 4.mov 9-14 Energy Sources for Contraction 1) Creatine phosphate 2) Cellular respiration • creatine phosphate – 9-15 Oxygen Debt Oxygen debt – • oxygen not available • glycolysis continues • • liver converts lactic acid to glucose 9-17 Muscle Fatigue • • commonly caused from • decreased blood flow • • • cramp – 9-18 Heat Production • by-product of cellular respiration • muscle cells are major source of body heat • blood transports heat throughout body 9-19 Muscular Responses Threshold Stimulus • Recording a Muscle Contraction • twitch • latent period • period of contraction • period of relaxation • refractory period • all-or-none response 9-20 Summation • process by which individual twitches combine • produces sustained contractions • can lead to tetanic contractions 9-21 Recruitment of Motor Units • recruitment - • whole muscle composed of many motor units • as intensity of stimulation increases, recruitment of motor units continues until all motor units are activated 9-22 Sustained Contractions • smaller motor units recruited first • larger motor units recruited later • • muscle tone – 9-23 Types of Contractions • isotonic – • eccentric – • concentric – • isometric – 9-24 Fast and Slow Twitch Muscle Fibers Slow-twitch fibers (type I) • • • • most myoglobin • good blood supply Fast-twitch fatigueresistant fibers (type IIb) • intermediate fibers • • • Fast-twitch glycolytic fibers (type II) • • • 9-25 Smooth Muscle Fibers Compared to skeletal muscle fibers • • single nucleus • elongated with tapering ends • myofilaments randomly organized • • lack transverse tubules • sarcoplasmic reticula not well developed 9-26 Smooth Muscle Contraction • Resembles skeletal muscle contraction • interaction between actin and myosin • both use calcium and ATP • both depend on impulses • Different from skeletal muscle contraction • smooth muscle lacks troponin • two neurotransmitters affect smooth muscle • • • stretching can trigger smooth muscle contraction • • 9-28 Cardiac Muscle • • muscle fibers joined together by intercalated discs • fibers branch • network of fibers contracts as a unit • self-exciting and rhythmic • longer refractory period than skeletal muscle 9-29 Skeletal Muscle Actions • origin – • insertion – • prime mover (agonist) – primarily responsible for movement • synergists – assist prime mover • antagonist – resist prime mover’s action and cause movement in the opposite direction 9-30 Major Skeletal Muscles 9-31 Major Skeletal Muscles 9-32 Life-Span Changes • myoglobin, ATP, and creatine phosphate decline • by age 80, half of muscle mass has atrophied • adipose cells and connective tissues replace muscle tissue • exercise helps to maintain muscle mass and function 9-65 Clinical Application Myasthenia Gravis • autoimmune disorder • receptors for acetylcholine on muscle cells are attacked • weak and easily fatigued muscles result • difficulty swallowing and chewing • ventilator needed if respiratory muscles are affected • treatments include • drugs that boost acetylcholine • removing thymus gland • immunosuppressant drugs • antibodies 9-66
