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physiology : muscular system

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part of dr . hanaa

part of dr . hanaa

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  • 1. Muscular System Locomotion ( movement of the parts or the whole body).
  • 2. Types of muscles • According to the histological structure 1- Striated muscles, contain striations. 2- Unstriated muscles, no striations (smooth). • According to the position : 1- Skeletal muscles, present around the skeleton. 2- Cardiac muscles, present in the heart. 3- Visceral muscles, present in the viscera and urinary bladder. • According to the ability of controlling the contraction: 1- Voluntary muscles, contract under our control. 2- Unvoluntary muscles, contract without control of us.
  • 3. Skeletal muscle
  • 4. • according to protein in myosin: two types: a) Slow unit * red - dark- respond slowly- long twitch duration (up to 100 ms) - low mitochondrial ATP ase activity , * Produce ATP slowly * In large limp muscle * Ex. marathon runners (more red fibers) b) Fast unit * Pale(white) - short twitch duration ( 7 ms) - * produce ATP quickly – more powerful contractions – fine ,skilled movement * Ex. Weighlifters
  • 5. Skeletal (voluntary; striated) muscle • Attach to skeleton • Function in movement (bone) • Contract voluntary C.N.S. neuromuscular junction • Connect to the bone through the beginning (origin) other end (insertion) • If the origin formed of 2 parts(Biceps) or 3 (Triceps) • Ends with tendons
  • 6. Structure Each muscle composed of many myofibrils(muscle fibers). Cylindrical shape, multinucleated. Each myofibril composed of many myofibrils . Each myofibril composed of many repeated sarcomeres. Myofibrile appear as alternated dark and light bands. Light band is called Isotropic band (I), Dark band is called Anisotropic band (A). Each sarcomere composed of many myofilaments. ( thin ) actin , troponin , tropomysin ( thick ) myosin .
  • 7. Molecular structure: Myosin: • Thick helical protein filament. • Consists of heads and tails. • By proteiolytic enzyme(trypsin) broken into: ** light meromyosin (LMM) : H-zone No ATPase activity and can’t combine with actin. No heads at the H-zone. ** Heavy meromyosin (HMM) contain ATP ase activity , can combine with actin. • Release the heads from the tails if treated with pepsin enzyme. • The head of the myosin molecule forms cross bridge with the adjacent actin filament.
  • 8. Actin: •Thin filaments actin with small amount of tropomyosin and troponin. •In ionic environment of the cell, actin exist in the fibrous form (F-actin) containing 2 chains of actin monomer coiled around each other. •In the absence of salts, actin becomes globular (G-actin). •The change from F- actin to G- actin is reversible and is called ( G F ) transformation;
  • 9. • Troponin and tropomyosin (Regulatory agent in muscle contraction) At rest ,tropomyosin block the binding of actin to myosin. • Troponin is formed of 3 subunits: Troponin (I) inhibit the interaction of myosin to actin. Troponin (C) which contain the binding sites of Ca++ that initiate the contraction of the myofilaments. Troponin (T) binds the other troponin component to tropomyosin.
  • 10. Classification according to the movement : • 1- a) Flexor; bends one part upon another. • b) Extensor; straightens or extends part. • 2- a) Adductor; draws a part towards the axis • b) Abductor; draws a part away of the axis • 3- a) Depressor; lowers a part. • b) Elevator; elevate or raise a part. • 4- a) Constrictor; constricts or close an organ. • b) Dilator; cause dilation of the same organ. • 5- Rotator Muscle; rotates on part on another
  • 11. CARDIAC MUSCLES:  They contract involuntary, and rythimitically.  They obey all or non law. They are auto stimulated (pace maker). Striated muscle  Pump blood  Adapted for resistant to fatigue **A lot mitochondria (aerobic respiration) **Numerous myoglobins (O2 storing pigment) **Good blood supply
  • 12. Intercalated discs (support contration) double membrane separating adjacent cells. Cell junctions fuse together the plasma membranes of cardiac muscle cells, allow the cells to contract as a unit.
  • 13. Smooth muscle Unstriated  Walls of hollow organs ( gastrointestinal tube & respiratory system )  Two types  multi-unit: without interconnection,iris  single-unit :(walls of viscera)
  • 14. Spindle shape –single nucleus  Arranged in sheets  Few mitochondria(depend on anaerobic glycolysis)  Contain myosin & actin (not arranged into sarcomeres)  Stimulated by Autonomic nervous system ( involuntary) Hormons ( vasoconstriction & vasodilators) adrenalin
  • 15. EFFECT OF STIMULUS: a- In skeletal Muscle: • Threshold Stimulus: no responds occur. • Minimal Stimulus: responds by minimal observed line. • Submaximal Stimulus: increasing the stimulus, the number of responding fibers increase • Maximum Stimulus: all muscle fibers contract. • Supra-maximum Stimulus: increasing the stimulus, no more effect. B- In cardiac Muscle: • Sub-minimal stimulus; no responds occur. • Threshold value; all muscle fibers respond,increasing stimulus no more effect will resulted.
  • 16. Steps of Contraction: • Release of transmitter at motor end plate. • Generation of action potential. • Inward spread of depolarization along T-tubules. • Release of Ca++ ions. • Binding of Ca++ ions to troponin C. • Uncovering myosin binding sites on actin. • Formation of cross-Linkage between actin and myosin • Sliding of actin over myosin, producing shortening.
  • 17. Steps Of Relaxation: •Ca++ ions pumped back into sarcoplasmic reticulum. •Release of Ca++ ions from troponin. •Cessation of interaction between actin and myosin.
  • 18. Changes accompanying muscle contraction: Thermal Change: Heat of contraction and relaxation. PH Changes: Accompanied the chemical changes, acid by splitting ATP or base by breakdown of CP. Electrical change: Direct or indirect depolarization through the connected nerve. Chemical change: (Aerobic or anaerobic) oxidative respiration, CP is an immediate source of ATP ( phosphrelate ADP).
  • 19. Mechanical changes: Sliding of actin filament over the myosin filaments, ( cross bridge).

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