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An Overview of Muscle Contraction PED 5230 The Systems • Neural • Muscular "He that wrestles with us strengthens our nerves and sharpens our skill. Our antagonist is our helper." Edmund Burke, British statesman, 1729-1797 Neural Neural Neural Neural Neural Neural Neural Neural • MOTOR UNIT • One motor nerve and all the muscle fibers it innervates • Type I - 1:10-100 • Type II - 1:1000s • All-or-none Neuromuscular Neuromuscular • Choline and Exercise • Acetylcholine levels do decrease during prolong exercise • Supplementing with choline does maintain Ach levels • Some studies show choline improves aerobic endurance performance but some studies show no effect; more studies are needed. • Lecithin/Choline and Health • Helps prevent memory loss, Alzheimer's disease, depression, and various psychiatric disorders; lower blood cholesterol; and even cure liver disease, cancer, and AIDS. • There are theories about how lecithin/choline may help against some of these disorders, but the clinical evidence is weak or nonexistent. • Full Article, Berkeley Wellness Letter, July 2002 "Great ideas originate in the muscles." Thomas Edison, the most famous American inventor who, singly or jointly, held a world record 1,093 patents. In addition, he created the world's first industrial research laboratory, 1847-1931. Muscle Facts • Muscle have several hundred to over 1 million muscle fibers • Muscle fibers: 35 – 450 mm long • A muscle fiber can have 200-300 nuclei per millimeter Muscle Anatomy • Epimysium, Endomysium, and Perimysium converge to form tendons and are very elastic Muscle Anatomy • Fiber (muscle cell) – Myofibrils • Myofilaments – Actin – Myosin Muscle Anatomy Muscle Anatomy Muscle Anatomy Muscle Anatomy Actin Myosin Muscle Anatomy Muscle Anatomy Muscle Anatomy • PROTEINS • Actin – Actin – Troponin I, C, and T – Tropomyosin • Myosin II (twisted golf clubs) – Heavy chain – determines fiber type (I, IIa, IIx, or IIb) – Light chain • Titin – largest protein inside muscle; attaches myosin • Nebulin – attaches actin • Others – Alpha-actinin – Tropomodulin Muscle Anatomy • SATELLITE CELLS • Satellite cells were identified over 40 years ago through electron microscopy. • Satellite cells are the committed stem cells of adult skeletal muscle. • Their major function is to repair, revitalize, and mediate skeletal muscle tissue and growth by differentiating into myocytes. • Satellite cells are normally non-proliferative. • They do become active, however, when skeletal muscle tissue is injured or heavily used during activities such as weight lifting or running. • Satellite cells are located at the surface of the basal lamina of the myofiber. Muscle Anatomy Muscle Anatomy • Muscle contains 75% water, 5% inorganic salts and 20% protein • Of the protein, 12% is contractile proteins and 8% is enzymes, membrane proteins, transport channels, and other proteins. • Myosin most abundant protein with approximately 300 myosin proteins in one thick filament. Muscle Contraction • ASSIGNMENT • Turn in an outline or listing of the major steps (at least 8) of muscle contraction written in your own words. • Univ. Calf. at Irvine • NISMAT Quick Time Movie • Yellow = Calcium • Green = ATP • Gray = ATPase • Two Quick Time movies of the contraction process can be download at the 5230 Web Page • Or, go to SDSU Slides of the Sliding Filament Theory ADP + P + energy ADP + P Energized New ATP Types of Muscle Contraction Muscle Contraction • TYPES OF MUSCLE CONTRACTION • Isometric (static) • Concentric (shortening) • Pliometric or Eccentric (lengthening) Muscle Contraction • CONCENTRIC • Myosin swivel • Actin slide inward • Muscle force is greater than the resistance or weight • i.e. Force (muscle) > Resistance (weight or outside resistance) • Therefore, sarcomere shortens Muscle Contraction • ISOMETRIC or STATIC • ’Iso’ = same • ’Metric’ = length • Myosin swivel • Actin does not slide • Why? • Force = Resistance • Therefore, sarcomere length doesn’t change • Example: pushing against a wall Muscle Contraction • ECCENTRIC • Myosin swivel • Actin may slide inward but... • …ultimately, actin slides away from each other. • Force < Resistance • Sarcomere gets longer • Example: lowering a weight Muscle Contraction • ECCENTRIC • Used to control agonist muscle • Example:triceps lowers dumbbell while biceps ’controls’ the lowering. • Generates greater tension. – Causes more damage than other types? • Greater repair required… • …producing a stronger muscle • Also, results in more muscle soreness. – Recruits more or different motor units? Muscle Contraction • Concentric - shortening • Isometric - same length • Eccentric – lengthening • With all three, myosin heads swivel. • With all three, ATP is required. • The difference is what actin is, or isn’t doing. Muscle Fiber Types "Every morning in Africa, a Gazelle wakes up. It knows it must run faster than the fastest lion or it will be killed. Every morning a Lion wakes up. It knows it must outrun the slowest Gazelle or it will starve to death. It doesn't matter whether you are a Lion or a Gazelle... when the sun comes up, you'd better be running." Unknown quotes Muscle Fiber Type • Myofibullar- ATPase (M-ATPase) • Succinate dehydrogenase (SDH) Muscle Fiber Type • Myosin heavy chain – Type I, – Type IIa, IIx, IIb Muscle Fiber Type Figure 18-15 Type IIb Motor Type IIa Motor Type I Motor Unit Hybrid Unit Unit IIb and IIx myosin IIx and IIa myosin I myosin heavy IIb, IIx, and I heavy chain heavy chain chain myosin heavy chain Fatiguable Fatiguable Fatigue Resistant Glycolytic Glycolytic Oxidative White Intermediate Red Phasic Phasic Tonic Fatigue Curves (see next slide) Twitch Response (see next slide) Muscle Fiber Type Type IIb Type IIa Type I Twitch Response Fatigue Curves Muscle Fiber Type • Twitch response • Fatigue curves Muscle Fiber Type Figure 18-18 • Order of recruitment; IIb additive IIa I Muscle Fiber Type • Number of motor units IIb • Graph showing % of fibers IIa used compared to the amount I of muscular force Muscle Fiber Type Architectural Factors • Series - velocity • Parallel – force • Pinnation allows for more sarcomeres Hypertrophy • Muscle hypertrophy can increase fiber diameter to the point where gas and nutrient exchange is limited thus limiting muscle endurance.
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