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Stefan Sivkov MU - Plovdiv Why do we study muscles? Body movement Skeletal movement Movement of blood Movement of food Uterine contractions Muscle disorders Food resource Weight control – Use it or loose it General characteristics 600 muscles - 40 % body weight Organ structure muscle, connective, nerve, epithelial tissue Functions • movement • heat production • posture control • support Embryogenesis Mesodermal origin Somites – primary mesodermal segments sclerotomes – vertebral column myotomes – muscles of body and limbs dorsal – back muscles ventral – antero-lateral and limb muscles Branchial gills – facial and neck muscles Topological organization of muscles Paired and symmetrical Segmental – in the body Shortest distance between origin and insertion Perpendicular to the joint axes Classification According to the form According to the fiber direction According to the function According the number of joints According to the position Structure of the muscle Contractile (fleshy) part Extrafusal muscle fibers Muscle fibers Muscle bundles Muscle Connective tissue in the muscle 1. Endomysium. Thin layer around the muscle fiber. 2. Perimysium. Thicker layer around a bundle of muscle fibers (fascicle). 3. Epimysium. The outer connective tissue layer. Muscle spindle Proprioreception Intrafusal muscle fibers thin (30 mm) and short (mm) central portion (nuclear bag) - sensory endings peripheral parts - motor endings of g-motoneurons Intrafusal fibers – nuclear bag and nuclear chain. Fusimotor fibers – motor nerve fibers. Primary (Іа) and secondary (ІІ) sensory nerve fibers. Registers changes in the muscle length and speed. Sensation is modulated from CNS by fusimotor system: - static gamma system for changes in length - dynamic gamma system for changes in speed. Muscle tendon Attachment of muscle form – according to the muscle form thickness – up to 20% muscle thickness structure – collagen fibers – peritendineum – between and around the fibers – Golgi corpuscles – stretch receptors – blood vessels – less than in the muscle Type I muscle fibers Lowest contractile velocity Lowest cross section surface Highest aerobic capacity Lowest anaerobic capacity Slow, long-term contraction. Long distance runners, swimmers Type II muscle fibers Type II-b fibers have Highest contractile velocity Highest cross section surface Lowest aerobic capacity Highest anaerobic capacity Quick, short-term contraction. Sprint, weight-lifting, fitness Type II-a fibers are intermediate. Auxiliary structures Fasciae proper – one muscle group – synergic muscles septae – separate neighbouring muscle groups Synovial vaginae Outer sheath Inner sheath Mesotenon Synovial bursae Beneath tendons and muscles, close to their insertions Sesamoid bones In tendons close to their insertions Histological characteristics of muscle fibers 1. Cross striation. а. Dark and light bands. 1) А-bands. Dark – anisotropic 2) І-bands. Light - isotropic. б.1) Z disc in І band. 2) Н zone in А band; М линия, dark in Н. Muscle biomechanics Internal biomechanics Physiological transection – perpendicular to fibers Anatomical transection – through the widest part of the muscle Vector of muscle strength Effectiveness of muscle strength - negatively proportional to the angle between the vector and the bone Muscle biomechanics External biomechanics Movements in joints. Synergists and antagonists Muscle strength. Number and length of the fibers External biomechanics Attachments punctum mobile - insertion punctum fixum - origin Levers of muscle contraction Fulcrum Point of load Point of strength I class lever – of equilibrium II class lever ІІА class – of strength ІІВ class – of speed Theory of sliding myofilaments Cycle of crossed bridges ATP required. Crossed bridges Myosin On both sides of the myofilaments Bidirectional on one side of the myofilament А-bandsdo not change І-bands narrow