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?
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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?
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- As mentioned in class, one additional major use of ATP in skeletal muscle (besides powering the myosin heads) is the recycling of calcium ions back into the sarcoplasmic reticulum after depolarization. The resting concentration of Ca++ in the muscle cell cytoplasm is about 50-100 nM, and the spike concentration after depolarization is about 10-20 μΜ. a) Consider a single sarcomere. What is the number of free calcium ions within the sarcomere at rest? What is the number of free calcium ions after depolarization? b) The major ion pump responsible for calcium ion recycling is SERCA (sarco/endoplasmic reticulum calcium ATPase). SERCA uses one molecule of ATP to pump two calcium ions, and the resting level can be restored in about 10-20 ms. How many molecules of ATP are used in a single sarcomere for pumping calcium in a single "twitch"? c) Assume that a single "twitch" is sufficient to drive one sarcomere from its fully extended length (about 2.5 µm) to its fully contracted length (about 1…Why does muscle CAP Amp for both the normal Ringer's solution and Ringer's solution with Neostigmine increased as the stimulus amplitude increased, but a normal Ringer's solution would have a larger muscle CAP Amp value? Why is this the same case for a CAP Period as stimulus amplitude increases?. Why would Muscle CAP Period values for Ringer's with NEO then have larger values. Why does a normal Ringer's solution take longer to reach maximum action potential ?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.
- 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.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)noneThe ability of myosin to walk along an actin filament may be observed with the aid of an appropriately equipped microscope. Describe how such assays are typically performed. Why is ATP required in these assays? How can such assays be used to determine the direction of myosin movement or the force produced by myosin?
- If ligand-gated K+ channels were to open in an unstimulated muscle fiber,how would this affect the resting membrane potential?Can you modify this experiment so that the mass lifted by the muscle contraction continues to increase for every trial? If yes, explain how it should be modified. If no, explain why.Explain the intracellular mechansim of smooth muscle relaxation of agaonist such as mepyrimine and atropine. Give diagram for each.
- ctions in smooth muscle cells depend on which one of the following activation steps? Ca2+-activated phosphorylation of myosin-II Ca²+ binding to troponin GTP binding to myosin-II Actin polymerization (b) (c) (d) Explain:Discuss the following statement: “The basal lam-ina of muscle fibers serves as a molecular bulletin board,in which adjoining cells can post messages that direct thedifferentiation and function of the underlying cells.”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