Chapter 12 Study Questions
1. Group 1 should become experts on the structure of a sarcomere. 2. Group 2 should become experts on the sliding filament theory. 3. Group 3 should become experts on the contractile cycle of skeletal muscle. 4. Group 4 should become experts on excitation-contraction coupling. 5. Group 5 should become experts on summation and tetanus. 6. Group 6 should become experts on smooth muscle contraction.
7. What are the three types of muscle found in the human body? Where can you find each, and what does each do? Cardiac – found in the heart
Smooth – internal organs and tubes, stomach, urinary bladder Skeletal – attached to bones
8. What controls the contraction of the different types of muscle? Autonomic innervations or spontaneously
9. Describe the arrangement of muscle fibers to make a muscle. Cell membrane called sarcolemma and cytoplasm called sarcoplasm. Arranged with their long axes in parallel. Each fiber is sheath in connective tissue with groups of adjacent fibers bundled together in units called fascicles. 10. Define the terms sarcolemma, sarcoplasm, myofibrils, sarcoplasmic reticulum, terminal cisternae, t-tubules. Sarcolemma is the cell membrane of a muscle fiber, sarcoplasm is the cytoplasm, myofibrils are highly organized bundles of contractile and elastic proteins that carry out the work of contraction, sarcoplasmic reticulum is a form of modified ER that wraps around each myofibril, terminal cisternae are enlarged regions at the ends of the tubules that concentrate and sequester Ca2+, and t-tubles are a branching network associated with terminal cisternae. 11. What is the function of t-tubules?
They rapidly move action potentials from the cell surface to the interior of the fiber. 12. What are the different proteins that make up a myofibril? Contractile proteins: Myosin and actin, regulatory proteins: tropomyosin and troponin, and accessory proteins: nebulin and titin. 13. What is the structure of thick filaments and thin filaments? Thin filaments are made of two F-actin polymer twisting together. Thick filaments are made of 250 myosin molecules. 14. Describe the structure of a crossbridge.
Crossbridges form when the myosin heads of thick filaments bind to actin in the thin filaments. 15. Describe the different elements of a sarcomere.
Z disks – zigzag protein structures that serve as the attachment site for thin filaments. I band – light colored bands that represent a region occupied only by thin filaments. A band – darkest band and encompasses the entire length of a thick filament H zone – thick filaments only in the central region of A band M line – represents proteins that form the attachment side for thick filaments. 16. What is the role of titin and nebulin?
Titin stabilizes the position of the contractile filaments and its elasticity returns stretched muscles to their resting length. Nebulin helps align the actin filaments of the sarcomere. 17. Explain the three major events that lead to skeletal muscle contraction. Events at the neuromuscular joint, excitation-contraction coupling, and contraction-relaxation cycle. 18. Explain the sliding filament theory of contraction. What parts of the sarcomere move, and which remain constant? Overlapping actin and myosin filaments of fixed length slide past one another in an energy-requiring process resulting in muscle contraction. 19. What happens during a power stroke? What provides the energy for this process? The actin filaments are pushed toward the center of the sarcomere. Calcium signal 20. Describe the role of calcium, troponin, and tropomyosin in muscle contraction. How do they also relate to relaxation? A calcium signal initiates contraction by binding to troponin. Troponin-calcium complex pulls tropomyosin away from actin’s myosin-binding site. Myosin binds to actin and completes power stroke....