11.2 - Movement

Essential Idea: The roles of the musculoskeletal system are movement, support, and protection. 11.2 Movement Understandings: Bones and exoskeletons provide anchorage for muscles to act as levers Synovial joints allow certain movements but not others Movement of the body requires muscles to work in antagonistic pairs Skeletal muscle fibers are mulitinucleate and contain specialized endoplasmic reticulum Muscle fibers contain many myofibrils Each myofibril is made up of contractile sarcomeres The contraction of the skeletal muscle is achieved by the sliding actin and myosin filaments ATP hydrolysis and cross bridge formation are necessary for filaments to slide Calcium ions and the proteins tropomyosin and troponin control muscle contractions Application: Antagonistic pairs of muscles in an insect leg Skills: Annotate a diagram of the human elbow Draw labelled diagrams of the structure of a sarcomere Analyze electron micrographs to find the state of contraction of muscle fibers

Endoskeletons and Exoskeletons A. Provide support and attachment points for muscles – act as levers B. Endo – inside body C. Exo – shell of chitin

Antagonistic pairs A. Pairs of muscle that accomplish opposite movements

Synovial Joints – provide movement

Muscle fibres (muscle cells) Contain multiple nuclei Plasma membrane = sarcolemma 1. Tunnel like extensions going into the cell called T-tubules

Cytoplasm = sarcoplasm 1. Organelles that store glycogen 2. Myoglobin – like hemoglobin, stores oxygen Myofibrils – stringy sections of a muscle cell 1. Lots of mitochondria packed between them 2. Composed of sarcomeres (contractile units)

V. Sarcomeres https://www.youtube.com/watch?v=jqy0i1KXUO4

VI. Steps of a Muscle Contraction https://www. youtube. com/watch

VI. Steps of a Muscle Contraction. 1 VI. Steps of a Muscle Contraction 1. At rest, Na+ is actively pumped out of the cell and K+ is actively pumped into the cell (requires ATP).

2. Neurotransmitter (chemical messenger in nervous system) called acetylcholine (Ach) is released by exocytosis at the neuromuscular junction (NMJ)

3. Ach diffuses across the NMJ and attaches to receptors on the muscle cell, causing sodium gates on the sarcolemma to open and let Na+ into the cell which causes K+ to leave the cell

4. If enough Ach is released, an “action potential” is generated (can’t stop once it has started) 5. At rest, actin and myosin are kept apart by troponin and tropomyosin and Ca++ is being actively transported into the SR

6. Change in Na+/K+ concentrations causes the SR to release Ca++ 7 6. Change in Na+/K+ concentrations causes the SR to release Ca++ 7. Ca++ attaches to troponin and tropomyosin, pulling them away from actin and exposing the myosin binding sites

8. Myosin heads bind to actin and start pulling the actin inward, shortening the sarcomere (a contraction)

9. As this is occurring, Ach is being broken down and its components are returning to the nerve cell 10. Once Ach is broken down, sodium gates and potassium gates close, and Na+ is actively pumped out and K+ is pumped into the muscle cell

11. Return of Na+/K+ concentrations causes SR to start taking Ca++ back in 12. Without Ca++, troponin and tropomyosin block myosin and actin from binding 13. Sarcomere relaxes

https://www.youtube.com/watch?v=7wM5_aUn2qs