the muscular system l.
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The Muscular System

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  1. The Muscular System Approximately 40% of your body weight is your muscle. Functions Muscles produce movement. When muscle contracts , it pulls insertion bone near origin bone. Movement occurs at joint between origin and insertion.  Origin– The bone that moves less, provides the area of attachment for the end of the muscle called the origin.

  2.  Insertion – the movable bone provides the surface for the muscle’s insertion. e.g. biceps : origin at the joint of humerus and scapula, insert on radius. triceps : origin at humerus, scapula and clavicle, inserts on ulna. • Biceps and triceps work in opposing pairs in an antagonistic system. • Groups of muscles usually contract to produce a single movement – synergistic pattern. e.g. extension of lower legs is by rectus femoris, gracilis and sartorius.

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  4. There are three different types of muscles a. skeletal muscle – voluntary, striated muscle. b. cardiac muscle – involuntary, striated (branching) muscle. c. smooth muscle – involuntary, non-striated muscle, e.g. Stomach, intestinal tract, urinary bladder and blood vessels. Reference:

  5. Skeletal Muscle Contraction Skeletal muscles contain thousands of muscle fibers (muscle cells). Each fiber consists of finer threadlike structures called myofibrils. Myofibrils contain two kinds of protein strands: thick filament, myosin, with side projecting cross-bridge. Thinner filament, actin. Repeating bands of actin and myosin translate into light – dark repeating unit that gives skeletal muscle its striped appearance. Dark line (Z) line between each repeating unit is defined as sacromere that is the fundamental unit of muscle contraction.

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  7. Muscle Structure Reference:

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  9. The Sliding-Filament Model Reference:

  10. Role of Calcium in Muscle Excitation and Contraction Coupling

  11. Role of Calcium in Muscle Excitation and Contraction Nerve ending release neuro transmitter at neuro-muscular junction – membrane excitation Sarcoplasmic reticulum release Ca 2+ Ca 2+ binds to troponin removing blocking action of tropomyosin Actin and myosin –cross bridge movement ATP is required Remove Ca 2+ from troponin restores blocking action of tropomyosin Ca2+ uptake (ATP required)

  12. Muscle Disorders • Muscular dystrophy – progressive weaken of the muscles. • Paralysis – loss of ability to produce voluntary movement. This is due to disease or injury of brain or spinal cord or nerve • Muscle atrophy – muscle shrinkage. Decrease in muscle size. • Muscle hypertrophy – increase in muscle size because of over work. e.g. heart frequently hypertrophy from over work.

  13. Muscle StructureFront View Back View Reference: