Skeletal Muscle: Structure and Function
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| Human body contains how many skeletal muscles? | over 400; which constitute 40-50% of total body weight
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| 3 Functions that Skeletal Muscle perform: | 1) Force generation for locomotion and breathing 2) force generation for postural support 3) heat production during periods of cold stress
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| Muscles attach to bone via... | tendons!
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| origin of muscle- | one end of muscle attached to bone that does not move
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| insertion point of muscle- | opposite muscle fixed to a bone that moves during muscle contraction
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| muscles that decrease joint angle are | flexors
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| muscles that increase joint angle are | extensors
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| epimysium | surrounds entire muscle
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| perimysium | surrounds individual bundles of muscle fibers
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| endomysium | connective tissue around each individual muscle fiber
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| basement membrane | just below endomysium, surrounding each muscle fiber- extra layer of protective tissue
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| sarcolemma | cell membrane surrounding muscle fiber cell
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| satellite cells | play role in muscle growth and repair, contribute to muscle growth during strength training
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| myonuclear division | cytoplasm surrounding each nucleus
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| more nuclei allow for.. | greater protein synthesis
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| myofibrils | contain contractile proteins actin (thin) and myosin (thick)
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| a sarcomere includes.. | Z line, M line, H zone, A band, I band
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| Sarcoplasmic reticulum (SR) | storage sites for calcium
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| transverse tubules extend from | sarcolemma ---> SR
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| motor unit- | the motor unit and the muscle fibers it innervates
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| neuromuscular junction | junction between motor neuron and muscle fiber
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| motor end plate | pocket formed around motor neuron by sarcolemma
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| neuromuscular cleft- | short gap between neuron and muscle fiber
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| acetylcholine being released from a motor neuron causes what.. | EPP- End Plate Potential
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| EPP is ALWAYS.. | large enough to exceed threshold and is signal to begin contractile process
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| The Sliding Filament Model | best explains the process of muscular contraction; andrew huxley and colleagues, actin and myosin interaction
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| First step of The General Process of Muscular Contraction | Myofilaments actin and myosin do not change length during muscle contraction
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| Second step of Muscular contraction | during contraction, actin myofilaments at each end of the sarcomere slide past the myosin filaments toward each other. Z discs become closer together as the sarcomere shortens.
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| Third step of Muscular contraction | As actin myofilaments slide over the myosin myofilaments, the H zones and I bands narrow. The A bands stay the same, they do NOT narrow.
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| Fourth step of muscular contraction | In a fully contracted muscle, the ends of the actin myofilaments overlap and the H zone disappears.
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| 3 Sources of ATP production in muscle contraction: | 1) phosphocreatine 2) glycolysis 3) oxidative phosphorylation
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| Excitation-Contracting coupling | sequence of events in which a nerve impulse (AP) reaches the muscle membrane and leads to shortening by cross-bridge activity
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| breakdown of ATP for contraction energy is by what enzyme?? | myosin ATPase (located of head of myosin cross-bridges)
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| power stroke | a single contraction cycle
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| when muscles are relaxed... | actin and myosin have a weak binding state
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| The 2 Regulatory Proteins which Control Muscular contraction (regulate interaction between actin and myosin) | troponin and tropomyosin
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| where are troponin and tropomyosin located? | on the actin molecule
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| in relaxed muscle, which protein blocks the active sites on actin molecules where myosin cross-bridges must attach? | tropomyosin
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| what is released from the SR that diffuses into muscles to bind to troponin? | Calcium
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| What is the trigger step in the detailed outline of muscular contraction? | When the AP reaches the SR and calcium is released and diffuses into the muscle to bind to the protein troponin.
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| The trigger for contraction to occur is linked to release of stored Ca++ from where? | lateral sac aka terminal cisternae of SR
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| In a resting (relaxed) muscle, the concentration of Ca++ is .. | very low
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| The contraction cycle can be repeated as long as... | there is free Ca++ available to bind to troponin and ATP can be hydrolized to provide the energy
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| what is muscle fatigue? | decline in muscle power output, decrease in force generation, decrease in shortening velocity
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| what causes muscle fatigue? | build up of hydrogen, lactic acid, high intensity, accumulation of ADP + Pi and free radicals, long duration exercises (2-4 hrs), disturbances in muscle/ extracellular electrolyte homeostasis
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| what are muscle cramps? | spasmodic, involuntary muscle contraction
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| what causes muscle cramps? | electrolyte depletion and dehydration theory
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