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REVIEW AND COMPARISON skeletal smooth cardiac
actin & myosin yes yes yes sarcomeres (banding) yes no yes t-tubules yes no yes sarcoplamic reticulum source of Ca SR SR & ECF SR & ECF speed of contraction fast/slow very slow slow spontaneous contraction no yes/no yes effect of nerve stimulation excit. excit./inhib. excit./inhib. stretch prod. contraction no yes/no yes
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Cardiac Muscle Autonomic Myogenic Slower contraction
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Smooth Muscle Parts of two muscle cells
Thick and thin filaments interdigitate, but not arranged in sarcomeres Thin filaments anchored to dense bodies Muscle fibers connected by gap junctions
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Muscle Energetics ATP 5 µmol•g-1 in fiber
µmol•g-1•min-1 needed muscle fiber myosin ATPase contraction relaxation SR Ca-ATPase creatine~P arginine~P ATP oxidative metab. glycolysis glycogen lactate O2 glucose lipids (amino acids)
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Although it takes a lot more glucose,
ATP can actually be produced faster by glycolysis than by oxidative phosphorylation: Rel. rate Glucose used Lactate prod. oxidative metabolism ATP glycolysis ATP
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Three types of vertebrate skeletal muscle fibers:
Fast glycolytic (white) (FG) Fast oxidative-glycolytic (FOG) Slow oxidative (red) (SO)
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White and Red Fibers
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FG FOG SO Speed of contraction fast fast slow Source of ATP glycolysis mixed oxid. met. Myoglobin content low intermed. high # mitochondria few many many # capillaries few intermed. many Glycogen content high intermed. low Lipid content low intermed. high Rate of fatigue fast intermed. slow
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Skeletal muscles may be a combination of fiber types:
e.g. cat soleus - postural muscle - all SO cat gastrocnemius - 45% FG, 25% FOG 25% SO, 5% FG/FOG Different fiber types can be recruited in response to exercise: e.g. gastrocnemius of sprinter - high in FG distance runners - high in FOG + SO
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Insect flight muscle: Time to relaxation in vert. striated muscle is msec. Some insect wings beat at > 1000 beats • s-1 (midge with wings clipped beats • s-1) Must have contraction/relaxation cycle of < 0.45 msec !! - surpasses electrical properties of the membrane
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Indirect or Asynchronous
Direct or Synchronous Indirect or Asynchronous
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1. Stretching of muscle induces contraction - no neural activity or depolarization necessary
2. Resonance of exoskeleton stores energy to stretch muscles: notum wing pleuron sternum
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