Stefan Sivkov MU - Plovdiv

Why do we study muscles? n Body movement n Skeletal movement n Movement of blood n Movement of food n Uterine contractions

n Muscle disorders n Food resource n Weight control –Use it or loose it

General characteristics  600 muscles - 40 % body weight  Organ structure  muscle, connective, nerve, epithelial tissue  Functions movementmovement heat productionheat production posture controlposture control supportsupport

Embryogenesis Mesodermal origin l Somites – primary mesodermal segments ç sclerotomes – vertebral column ç myotomes – muscles of body and limbs n dorsal – back muscles n ventral – antero-lateral and limb muscles l Branchial gills – facial and neck muscles

Topological organization of muscles l Paired and symmetrical l Segmental – in the body l Shortest distance between origin and insertion l Perpendicular to the joint axes

Classification l According to the form l According to the fiber direction l According to the function l According the number of joints l According to the position

Structure of the muscle Contractile (fleshy) part l Extrafusal muscle fibers ç Muscle fibers ç Muscle bundles çMuscle

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 l Proprioreception l Intrafusal muscle fibers l thin (30 mm) and short (mm) l central portion (nuclear bag) - sensory endings l peripheral parts - motor endings of  -motoneurons

n Intrafusal fibers – nuclear bag and nuclear chain. n Fusimotor fibers – motor nerve fibers. n Primary (Іа) and secondary (ІІ) sensory nerve fibers. n 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. - dynamic gamma system for changes in speed.

Muscle tendon Attachment of muscle l form – according to the muscle form l thickness – up to 20% muscle thickness l structure – collagen fibers – peritendineum – between and around the fibers – Golgi corpuscles – stretch receptors – blood vessels – less than in the muscle

Type I muscle fibers n Lowest contractile velocity n Lowest cross section surface n Highest aerobic capacity n Lowest anaerobic capacity n Slow, long-term contraction. n Long distance runners, swimmers

Type II muscle fibers Type II-b fibers have n Highest contractile velocity n Highest cross section surface n Lowest aerobic capacity n Highest anaerobic capacity n Quick, short-term contraction. n Sprint, weight-lifting, fitness Type II-a fibers are intermediate.

Auxiliary structures l Fasciae çproper – one muscle çgroup – synergic muscles çseptae – separate neighbouring muscle groups

l Synovial vaginae ç Outer sheath ç Inner sheath ç Mesotenon

l Synovial bursae çBeneath tendons and muscles, close to their insertions ç Sesamoid bones çIn 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 l Physiological transection – perpendicular to fibers l Anatomical transection – through the widest part of the muscle l Vector of muscle strength l Effectiveness of muscle strength - negatively proportional to the angle between the vector and the bone

Muscle biomechanics External biomechanics Movements in joints. l Synergists and antagonists Muscle strength. l Number and length of the fibers

External biomechanics Attachments çpunctum mobile - insertion çpunctum fixum - origin Levers of muscle contraction 2 Fulcrum 2 Point of load 2 Point of strength l I class lever – of equilibrium l II class lever 2 ІІА class – of strength 2 ІІВ class – of speed

Theory of sliding myofilaments Cycle of crossed bridges ATP required. l Crossed bridges çMyosin çOn both sides of the myofilaments çBidirectional on one side of the myofilament l А-bandsdo not change l І-bands narrow