Question

(9/25/25) formative assessment assignment: chapter 6 the muscular system part 1 (suggest 14 of 16 mechanism of muscle contraction: the sliding filament theory what causes the filaments to slide? this question brings us back to the myosin heads that protrude all around the ends of the thick filaments. when the nervous system activates muscle fibers as just described, the (1. ) heads attach to binding sites on the thin filaments, and the sliding begins. each cross bridge attaches and detaches several times during a contraction, generating tension that helps pull the thin filaments toward the center of the sarcomere. this “walking” of the myosin cross bridges, or heads, along the thin filaments during muscle (2. ) is much like a centipede’s gait. some myosin heads (\legs\) are always in contact with actin (\the ground\), so that the thin filaments cannot slide backward, and this cycle repeats again and again during contraction. as this event occurs simultaneously in sarcomeres throughout the muscle fiber, the cell shortens (figure 6.7). notice that the myofilaments themselves do not shorten during contraction; they simply (3. ) past each other. the formation of cross bridges—when the myosin heads attach to actin—requires calcium ions (ca2+) and atp (to \energize\ the myosin heads). so where does the calcium come from? action potentials pass deep into the muscle fiber along membranous tubules that fold inward from the sarcolemma. inside the cell, the action potentials stimulate the (4. ) reticulum to release calcium ions into the cytoplasm. the calcium ions trigger the binding of myosin to actin, initiating filament sliding (figure 6.8, p. 192). when the action potential ends, calcium ions are immediately returned to the sr storage areas, the regulatory proteins return to their resting shape and block myosin - binding sites, and the muscle fiber (5. ) and settles back to its original length. this whole series of events takes a few thousandths of a second. o 1. relaxes 2. myosin 3. shortening 4. slide 5. sarcoplasmic o 1. myosin 2. shortening 3. slide 4. sarcoplasmic 5. relaxes o 1. slide 2. sarcoplasmic 3. relaxes 4. myosin 5. shortening o 1. shortening 2. slide 3. sarcoplasmic 4. relaxes 5. myosin o 1. sarcoplasmic 2. relaxes 3. myosin 4. shortening 5. slide

Explanation:

The sliding - filament theory of muscle contraction involves myosin heads attaching to thin filaments (actin). During contraction, myosin cross - bridges "walk" along thin filaments, and myofilaments slide past each other. Calcium ions are released from the sarcoplasmic reticulum to trigger cross - bridge formation. When the action potential ends, the muscle fiber relaxes.

Answer:

1. myosin 2. shortening 3. slide 4. sarcoplasmic 5. relaxes