Slides 21 - Muscle systems

The rattlesnake tail shaker muscle can contract at

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Unformatted text preview: ialized for high-frequency contraction. • The rattlesnake tail shaker muscle can contract at 100 Hz. • What makes a sonic muscle able to contract so quickly? Sonic muscles 1.Myosin detachment rates are 6x faster than in FG fibres. 2.Perforations in the Z-disk allow for thick filaments to penetrate adjacent sarcomeres. 3.Very fast Ca2+ transient • Sonic muscle have very abundant SR that yield rapid release and uptake of Ca2+ • Sonic muscle TnC releases Ca2+ more quickly than other isoforms. Cicada tymbals Toadfish swim bladder muscle toadfish muscles • The fastest vertebrate skeletal muscle is the toadfish sonic muscle. • Ca2+ transients occur as fast as 200 Hz. - The Ca2+ transient is the very brief increase in cytoplasmic Ca2+ levels due to release and re-uptake in the SR. • Vertebrate muscles cannot be induced to contract faster due the limits of the vertebrate EC coupling machinery. Note that the time axes are different mechanisms and activated permeabilized (‘‘skin fibers with high and steady Ca2 concentrations. Un RESULTS AND DISCUSSION activating conditions, we found that the steady fo We found that intact swimbladder fibers contract and relax sectional area of myofibrils was still very low, 56 k very rapidly but generate extremely low forces. Toadfish 1 4 that of the other fiber types (Table 1). Force d fast-twitch white and slow-twitch red fibers used for swimming significantly compared with that of the intact mu generate normal forces of about 244 kN m2 and 192 kN m2 Given that activation is maximal, low force pro [note that when the red muscle value is corrected for 20%–30% result from either few attached crossbridges or mitochondrial volume (30), force per cross-sectional area of attached crossbridge (31). To estimate the myofibrils is almost the same for the two fiber types]. By attached crossbridges, we compared the stiffne contrast, the swimbladder fibers generate only about 1 10 that force in response to a quick length change) in the value or 24 kN m2 (Fig. 1). Because of the high content of SR fiber to that of the muscle fiber in rigor (32), required for rapid reuptake of Ca2 in the swimb...
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