![]() ![]() ![]() ![]() Asthe thin filaments slide inward, the I band and H zone narrow and eventuallydisappear altogether when the muscle is maximally contracted.However, the width of the A band and the individual lengths of the thickand thin filaments remain unchanged. Theymay even move so far inward that their ends overlap (Figure 10.5c). As a result, thethin filaments slide inward and meet at the center of a sarcomere. The model describing this process is known as the slidingfilament mechanism.The Sliding Filament MechanismMuscle contraction occurs because myosin heads attach to and “walk”along the thin filaments at both ends of a sarcomere, progressively pullingthe thin filaments toward the M line (Figure 10.5). It had been thought that muscle contractionmust be a folding process, somewhat like closing an accordion.Instead, researchers discovered that skeletal muscle shortens duringcontraction because the thick and thin filaments slide past oneanother. ![]() Describe how muscle action potentials arise at the neuromuscularjunction.When scientists examined the first electron micrographs of skeletalmuscle in the mid-1950s, they were surprised to see that the lengthsof the thick and thin filaments were the same in both relaxed andcontracted muscle.Outline the steps involved in the sliding filament mechanismof muscle contraction.304 CHAPTER 10 Muscular Tissue10.3 Contraction and Relaxationof Skeletal Muscle FibersOBJECTIVES ![]()
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