Muscle Structure & Function PDF

 Axial: Consists of the skull, vertebral column (C1‐coccyx), ribs, and sternum  Appendicular: Consists of shoulder girdle; bones of the arms, wrists, hands, and pelvic girdle; and bones of the legs, ankles, and feet Fig. 1.1. Haff et al. 2016. Essentials of St...

 Axial: Consists of the skull, vertebral column (C1‐coccyx), ribs, and sternum  Appendicular: Consists of shoulder girdle; bones of the arms, wrists, hands, and pelvic girdle; and bones of the legs, ankles, and feet Fig. 1.1. Haff et al. 2016. Essentials of Strength… Human Kinetics   Human body contains over 400 skeletal muscles 40‐50% of total body weight  Muscle shortening (contraction) pulls on boney levers to cause movement.  Functions of skeletal muscle 1) Force production for locomotion 2) Postural support & breathing 3) Heat production during cold stress 4) Major site of glucose disposal 3   Features: Striated Multi‐nucleated Sarcomeres are functional units 4  Sarcomere Sliding Filament Model of Muscle Contraction  Myofilaments (actin & myosin) slide past each other towards the center of the sarcomere  Sarcomere shortens as the Z‐line move towards the center of the sarcomere  Filaments overlap more making the I‐band and H‐zone disappear Fig. 1.7. Haff et al. 2016. Essentials of Strength… Human Kinetics http://bcove.me/s98cyu6q 5 6   Each muscle is made up of thousands of cylindrical cells called fibers that lie parallel to each other  Composition  Water = 75% (sarcoplasm)  Protein = 20% (e.g. actin, myosin)  Salts and other substances = 5%  Myofilaments consist of actin and myosin that account for ~85% of the myofibrillar complex  Other proteins either serve a structural function or affect protein filament interaction during muscle action  Tropomyosin, troponin, titin, α‐actinin, β‐actinin, M protein, and C protein 7   A single multinucleated muscle fiber contains myofibrils that that lie parallel to the fiber’s long axis  Myofibrils contain smaller subunits called myofilaments that lie parallel to the myofibril  Muscle > fascicle > muscle fiber > myofibril > myofilaments  Muscle fiber = muscle cell = myocyte = myofiber Fig. 1.1. Haff et al. 2016. Essentials of Strength… Human Kinetics 8   Each of the body’s skeletal muscles contains various wrappings of fibrous connective tissue (fascia) Epimysium (the outer layer) Perimysium (surrounding each fasciculus, or group of fibers) Endomysium (surrounding individual fibers) Fig. 1.3. Haff et al. 2016. Essentials of Strength… 9 Human Kinetics   All the connective tissue is continuous with the tendon. Tendon intermesh with collagenous fibers of bone periosteum. Tension developed in a muscle fiber is transmitted directly to the tendon & bone. Fig. 1.3. Haff et al. 2016. Essentials of Strength… 10 Human Kinetics  Watch: https://www.youtube.com/wa tch?v=7O_ZHyPeIIA (to 1:12) https://www.youtube.com/wa tch?v=InIha7bCTjM Fig. 18.17. McArdle et al. 2015. Exercise 12 Physiology… LWW  Crossbridge formation / cycling & power stroke / contraction 13 Fig. 18.17. McArdle et al. 2015. Exercise Physiology… LWW  Action Potential (AP) Excitation‐ Axon terminal Contraction Coupling Acetylcholine (Ach) Binds to receptors on sarcolemma Sarcoplasmic AP travels to T‐tubules reticulum(SR) Ca2+ released Ca binds to Tropomyosin shifts into sarcoplasm Troponin Myosin binds to active Power stroke & site to form crossbridge sliding of filaments  Explain the sliding filament model and how the zones and bands in muscle fibers change length  Describe the layers that compose the muscle fiber structure and the layers of fascia that surround them  Know the sequence of steps in excitation‐ contraction coupling   Haff & Triplett. Essentials of Strength Training & Conditioning, 4th edition. Human Kinetics, 2016.  Kenney, Wilmore, Costill. Physiology of Sport & Exercise, 6th edition. Human Kinetics, 2015.  McCardle, Katch, Katch. Exercise Physiology: Nutrition, Energy, and Human Performance, 8th edition. Wolters Kluwer Health, 2015. 16