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43 Cards in this Set
- Front
- Back
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What key roles does ATP play in muscle contraction?
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It must bind to the myosin head in order for myosin to detach from actin; It must be hydrolyzed to enable re-cocking of the myosin head; it is required for uptake of Ca by pumps in the SR. ATP also fuels calcium pumps in the PM, which is especially important in cardiac and smooth muscle, where more Ca comes from outside the cell. It also fuels the Na/K pumps.
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What is the backup system in muscle cells to ensure there's an ATP supply?
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ATP and creatine are created from phosphocreatine and ADP. Muscle contains a lot of phosphocreatine for this reason.
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What is isometric contraction?
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Generation of tension with no change in muscle length.
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What is isotonic contraction?
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A shortening of muscle with a constant load.
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What is the series elastic component?
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Slack. Tendons, ligaments, z-line material, cross bridges all create slack which must be taken up before muscle shortening occurs. This promotes smooth, graded movements.
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What's the parallel elastic component?
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Connective tissue sheath around the muscle. Only activated when muscle is stretched to 150% of its resting length. It runs in parallel with the sarcomeres.
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What happens to the crossbridges with increasingly heavy loads?
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As load increases, more cross bridges are needed just to balance the load, and less are available to move it. Eventually, all crossbridges are used just balancing the load and it can't move (maximum load).
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A single AP produces a single ____.
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Twitch.
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What results from temporal summation of APs?
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Tetanus--maximal contraction resulting from repetitive stimulation at high frequency.
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What is the chemical cause behind tetanus?
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An accumulation of intracellular Ca; there isn't enough time between APs for Ca to be pumped back into the SR.
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Why don't APs sum?
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The absolute refractory period. Na channels become inactivated.
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What is a motor unit?
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A single motorneuron and all the muscle fibers it innervates.
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What is spatial summation?
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Recruitment of multiple motor units by increasing stimulus strength.
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What types of sensory receptors control skeletal muscle contraction?
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Muscle spindles and Golgi tendon organs.
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Why don't APs sum?
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The absolute refractory period. Na channels become inactivated.
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What are muscle spindles?
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Specialized "intrafusal" muscle fibers arranged in parallel with, and mingled among, normal "extrafusal" muscle fibers that generate force.
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What is a motor unit?
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A single motorneuron and all the muscle fibers it innervates.
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What function do muscle spindles serve?
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They report muscle length and the rate of muscle stretch. When the muscle contracts, they become slack and are stimulated by efferent neural input to shorten iot remain responsive to changes in the extrafusal fiber length.
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What is spatial summation?
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Recruitment of multiple motor units by increasing stimulus strength.
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What are Golgi tendon organs?
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Bare nerve endings that are intertwined among the collagen matrix of the tendon near where it connects to the muscle.
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What types of sensory receptors control skeletal muscle contraction?
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Muscle spindles and Golgi tendon organs.
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How do Golgi tendon organs work?
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They report the force generated by the muscle. When muscles contract or are passively stretched, the tension in the tendon compresses the Golgi tendon organ, leading to firing of APs which give feedback to the brain.
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What are muscle spindles?
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Specialized "intrafusal" muscle fibers arranged in parallel with, and mingled among, normal "extrafusal" muscle fibers that generate force.
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How do smooth muscle cells differ from skeletal muscle cells?
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They lack T-tubules and sarcomeres; their actin and myosin are molecularly different; they lack the troponin regulatory system; Ca for contraction comes from outside the cell; contraction/relaxation is much slower; some cells are electrically coupled and some are very responsive to stretch.
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What function do muscle spindles serve?
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They report muscle length and the rate of muscle stretch. When the muscle contracts, they become slack and are stimulated by efferent neural input to shorten iot remain responsive to changes in the extrafusal fiber length.
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Does smooth muscle use the sliding filament method of contraction?
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Yes, there are still thin/thick filaments.
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What are Golgi tendon organs?
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Bare nerve endings that are intertwined among the collagen matrix of the tendon near where it connects to the muscle.
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How do Golgi tendon organs work?
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They report the force generated by the muscle. When muscles contract or are passively stretched, the tension in the tendon compresses the Golgi tendon organ, leading to firing of APs which give feedback to the brain.
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How do smooth muscle cells differ from skeletal muscle cells?
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They lack T-tubules and sarcomeres; their actin and myosin are molecularly different; they lack the troponin regulatory system; Ca for contraction comes from outside the cell; contraction/relaxation is much slower; some cells are electrically coupled and some are very responsive to stretch.
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Does smooth muscle use the sliding filament method of contraction?
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Yes, there are still thin/thick filaments.
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How are the actin and myosin different in smooth muscle cells?
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Smooth muscle myosin has only one tenth the ATPase activity as in skeletal muscle.
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How does Ca stimulate contraction in smooth muscle?
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Ca binds to calmodulin. That complex binds to myosin light chain kinase, which phosphorylates the light chain of myosin, allowing the heavy chain to bind actin. Relaxation requires dephosphorylation of the myosin by a phosphatase.
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How do smooth muscle cells get Ca?
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Most comes from the cell exterior via voltage-gated Ca channels in the PM. Some does come from intracellular SR. Ca removal during relaxation is done by pumps in the PM and SR, as well as Na/Ca exchange carriers in the PM.
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How are some smooth muscle cells electrically coupled?
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Gap junctions, also gives them intrinsic pacemaker activity.
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What's the usefulness of stretch sensitivity in smooth muscle?
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When the gut is stretched by food, smooth muscle cells respond by contracting and leading to peristalsis.
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How is cardiac muscle similar to smooth muscle?
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Gap junctions, electrical coupling, pacemaker activity, and use of extracellular Ca via V-gated Ca channels.
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How is cardiac muscle similar to skeletal muscle?
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It's striated (has sarcomeres), has T-tubules, troponin regulation, and has a similar contraction mechanism.
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What line of the sarcomere do the T-tubules come in at?
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The Z line.
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What does the heavy myosin head do?
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Binds actin and hydrolyzes ATP.
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What does the light myosin head do?
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Modulates ATPase activity of heavy chains.
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What are the 4 steps of the sliding filament model?
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1) Myosin head + ADP + P, binds to actin filament when Ca is present.
2) Binding causes release of P, then ADP, and the myosin head power strokes. 3) ATP binds to myosin and myosin releases from actin. 4) ATP is hydrolyzed to ADP + P and myosin re-cocks its head. Rinse and repeat. |
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What are the names/roles of the troponin subunits?
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T- Binds tropomyosin
I- Binds actin C- Binds Ca++ |
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How, in fact, do T-tubules actually elicit the release of Ca from SR?
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Ryanodine receptors serve as direct mechanical connections between Ca release channels in the SR membrane and the voltage-gated Ca channels in the T-tubule. Additionally, there is further activation of the Ca release channels by Ca ions entering the cytoplasm from the T-tubule ("Ca induced Ca release"). Ca induced Ca release is most important in cardiac muscle, where there are NO Ryanodine receptors.
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