state, the myosin head binds to actin. Upon the release of ADP and Pi the stored energy is also released, resulting in a “power stroke” which essentially moves the myosin head along the actin. The exponential repetition of this cycle generates muscle contraction. This interaction that occurs can also be known as a “cross-bridge cycle”, shown in Figure 3. Figure 5: Cross bridge cycle of actin and myosin in the presence of ATP. Source: In each cardiac muscle cell, there are many myofibrils that are composed of a repeating array of sarcomeres, which are the basic unit of contraction. Each sarcomere is made up of the thick and thin filaments, as shown in Figure 4. The thick filaments are composed of the myosin II bipolar filaments. The thin filaments are composed of the actin filaments which are assembled with their (+) ends orientated in the same direction, towards the Z disk. During the cross-bridge cycle, the myosin heads move toward the Z-disk and essentially shorten the sarcomere and thus the muscle contracts. Figure 6: Sarcomere contracted and relaxed. Source:
state, the myosin head binds to actin. Upon the release of ADP and Pi the stored energy is also released, resulting in a “power stroke” which essentially moves the myosin head along the actin. The exponential repetition of this cycle generates muscle contraction. This interaction that occurs can also be known as a “cross-bridge cycle”, shown in Figure 3. Figure 5: Cross bridge cycle of actin and myosin in the presence of ATP. Source: In each cardiac muscle cell, there are many myofibrils that are composed of a repeating array of sarcomeres, which are the basic unit of contraction. Each sarcomere is made up of the thick and thin filaments, as shown in Figure 4. The thick filaments are composed of the myosin II bipolar filaments. The thin filaments are composed of the actin filaments which are assembled with their (+) ends orientated in the same direction, towards the Z disk. During the cross-bridge cycle, the myosin heads move toward the Z-disk and essentially shorten the sarcomere and thus the muscle contracts. Figure 6: Sarcomere contracted and relaxed. Source:
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