In a study of aging in dolphins that were stranded on the beach, researchers took muscle biopsies and stained them for the fast isoform of myosin heavy chain. (Blue = stain for the fast isoform). Image A on the left is from a young dolphin and Image B on the right is from an old dolphin. If you could use the muscles in an experiment similar to the one in Rome et al, which one would reach tetanus at a lower stimulation frequency? Justify your answer (3 sentences max)
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- The single-fiber twitch experiments shown here were generated by stimulating the muscle cell membranes to threshold with an electrode and measuring the resulting action potential and force. How would the results differ if Ca21 were removed from the extracellular solution just before the electrical stimulus was applied?The sliding filament model depicts how myosin motors attached to actin lead to muscle contraction. This process proceeds in a precise series of events. Indicate which of the following shows the correct order of steps in the sliding filament model. Group of answer choices Myosin binds ATP; myosin tightly binds actin; power stroke; myosin releases actin Myosin binds GTP; myosin releases actin; power stroke; myosin tightly binds actin Actin binds ATP; power stroke; myosin tightly binds actin; actin releases ADP Actin binds ADP; myosin releases actin; power stroke; actin releases ADPWhich of the following step(s) about the excitation of skeletal muscle is/are incorrect? 1. Acetylcholine is released and binds to motor end plate receptors 2. An action potential is created and moves down T-tubules 3. Calcium is released from the sarcoplasmic reticulum 4. Calcium ions bind to tropomyosin to shift troponin off the binding sites for cross-bridging 5. Myosin forms cross-bridges and binds with actin to pull it towards middle of sarcomere
- A study of muscle fibers between chimpanzees and humans revealed that although muscle mass per body size are approximately equivalent, the ratio of red (slow) and white (fast) fibers were significantly different. Chimps tend to have a ratio of 30% red to 70% white where humans are 60/40 respectively. Speculate about what this ratio difference means in terms of muscle activity potential and a possible evolutionary significance of this difference.What happens to contraction of a muscle cell if some of the Ca2+ that was released during a contraction is still in the cytoplasm (sarcoplasm) when the next stimulus arrives? - The muscle contracts with the same tension generated as during the first contraction, because the number of cross-bridges formed is always the same during a contraction. - The muscle contracts with greater tension generated because more troponin molecules bound means greater myosin-binding sites (active sites) are revealed on the actin, leading to a larger number of cross-bridges formed. - The muscle contracts with greater tension generated because there will be more Ca2+ in the sarcoplasm after the second stimulation, which will bind to more troponin molecules. - The muscle contracts with the same tension generated as during the first contraction, because muscles contract in an all-or-none fashion.With regard to muscle contraction, which of the following is an INCORRECT statement with regard to the interactions of filaments that occur in the sarcomere? A. When muscles are relaxed tropomyosin blocks binding sites on actin subunits, which keeps cross-bridges from forming. B. The myosin heads conduct a power stroke motion to slide when bound to actin, to move the "thin" filaments towards the center of the sarcomere. C. During contraction, actin subunits are removed from the ends of the "thin" filaments to shorten actin polymers, thus reducing the length of the sarcomere. D. "Thick" filaments are anchored at the M-line, while "thin" filaments are anchored at the Z-line. E. Numerous myosin heads engage with the actin filaments simultaneously, such that there is no back-slipping during the contraction process.
- Skeletal muscle cells undergo contractions based on a molecular mechanism involving: 1)the sliding of actin and myosin filaments past each other without any change in filament length 2) the shortening of actin filaments following direct interaction with myosin 3) dynamic instability of microtubules 4)noneAn unexpected discovery from studies of ameboid movement is that the same proteins found in the contractile system of animal muscle—actin and myosin—are present in ameboid cells. Explain how these and other proteins interact during ameboid movement.Put these events that occur in skeletal muscle in the correct chronological sequence: 1. Activation of voltage-gated dihydropyridine (DHP) receptor in the T-tubule 2. Opening of mechanically-gated ryanodine receptors (RyR) on the sarcoplasmic reticulum 3. Na+ influx through ligand-gated ion channels on the motor end plate 4. Ca2+ binding to troponin 2, 1, 4, 3 4, 3, 2, 1 4, 3, 1, 2 3, 1, 4, 2 3, 1, 2, 4
- Describe in details the biochemical and mechanochemical series of events that enables motor neurons to trigger muscle contraction, using the biceps brachii as an example.First, explain how resting membrane potential is established in terms of ion concentration and electric charge. Next, explain the process of neural signal transmission from an alpha motor neuron to the muscle fiber. Do this by explaining how an AP is generated (ions and membrane proteins) at the neuron, how the signal is propagated, what happens at the axon terminal, what happens at the motor endplate, and explain all the molecular events that occur to cause muscle contraction.Put these events that occur in skeletal muscle in the correct chronological sequence: 1. Opening of mechanically-gated ryanodine receptors (RyR) on the sarcoplasmic reticulum 2. Ca²+ binding to troponin to initiate contraction 3. Activation of voltage-gated dihydropyridine (DHP) receptor in the T-tubule 4. Na+ influx through ligand-gated ion channels on the motor end plate 4, 3, 2, 1 2, 1, 4, 3 3, 1, 2, 4 4, 3, 1, 2 3, 1, 4, 2