55555555 - guest1 - Printable Version +- USMLE Forum - Largest USMLE Community (https://www.usmleforum.com) +-- Forum: USMLE Forum (https://www.usmleforum.com/forumdisplay.php?fid=1) +--- Forum: Step 1 (https://www.usmleforum.com/forumdisplay.php?fid=2) +--- Thread: 55555555 - guest1 (/showthread.php?tid=305811) |
55555555 - guest1 - ArchivalUser - 05-27-2008 When comparing the contractile responses in smooth and skeletal muscle, which of the following is most different? a. The source of activator calcium b. The role of calcium in initiating contraction c. The mechanism of force generation d. The source of energy used during contraction e. The nature of the contractile proteins 0 - ArchivalUser - 05-27-2008 a. 0 - ArchivalUser - 05-27-2008 for this i thought A too.... but ans is BBBB The greatest difference in excitation-contraction coupling involves the role of calcium in initiating contraction. In smooth muscle, calcium binds to and activates calmodulin, which, by activating myosin light chain kinase (MLCK), catalyzes the phosphorylation of the 20,000-Da myosin light chain (LC20). Once the light chains are phosphorylated, myosin cross-bridges bind to actin on the thin filaments, which initiates contraction. In skeletal muscle, calcium binds to troponin, which removes the tropomyosin-mediated inhibition of the actin-myosin interactions. Once the inhibition is removed, cross-bridge cycling (and contraction) begins. In both smooth and skeletal muscle, force is generated by the cycling of cross-bridges. ATP provides the energy for the cycling of the crossbridges in both muscles. In skeletal muscle, activator calcium comes exclusively from the sarcoplasmic reticulum (SR), while in smooth muscle, calcium can come from both the SR and the extracellular fluid. 0 - ArchivalUser - 05-27-2008 great..thx 0 - ArchivalUser - 05-27-2008 URW |