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The muscular system How skeletal muscle works A few words about cardiac and smooth muscle Organization of skeletal muscl

The muscular system How skeletal muscle works A few words about cardiac and smooth muscle Organization of skeletal muscle The major muscle groups. The skeletal muscle cell: the muscle fiber May be as long as the muscle itself Several nuclei and many mitochondria

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The muscular system How skeletal muscle works A few words about cardiac and smooth muscle Organization of skeletal muscl

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  1. The muscular system How skeletal muscle works A few words about cardiac and smooth muscle Organization of skeletal muscle The major muscle groups

  2. The skeletal muscle cell: the muscle fiber May be as long as the muscle itself Several nuclei and many mitochondria Extensive sarcoplasmic reticulum Striations due to actin and myosin filaments (myofibrils)

  3. Sarcomere- functional unit (note “sarco” prefix) During muscle contraction these shorten Characteristic patterns seen: I, A, H bands, etc.

  4. Neuromuscular junction

  5. A motor unit

  6. How does a muscle fiber contract? “sliding filament” model Myosin filaments contain cross-bridges pulling actin shortens sarcomere Requirement for ATP and calcium Action triggered by acetylcholine Stopped by breakdown of the enzyme (see p. 178)

  7. Sources for ATP? Respiration (aerobic and anaerobic) anaerobic when oxygen runs out pyruvate is converted to lactic acid fatigue lactic acid is carried in blood to liver, and converted back to glucose Creatine phosphate Myoglobin Heat produced in process; helps sustain body temperature

  8. Responses of single muscle fiber threshold stimulus if this is achieved, muscle will contract fully (all-or-none) Slow fibers- weak contraction, resist fatigue contain more blood flow,mitochondria aerobic exercise enhances development Fast fibers- strong contraction, fatigue easily anaerobic exercise will increase number of filaments in a cell (not more cells)

  9. A muscle fiber can be stimulated many times (summation) so that it cannot relax between twitches Tetany- sustained contraction More than one motor unit can be stimulated, too for sustained muscle work Muscle tone- some contraction is sustained

  10. Smooth muscle contains actin and myosin filaments; arranged differently from skeletal muscle Regulated differently- calmodulin Multiunit- separate fibers iris, blood vessel walls Visceral (internal organs) stimulus is transmitted from one cell to another Rhythmicity- pattern of contractions self-activated

  11. Smooth muscle contraction controlled by acetylcholine and norepinephrine Neurotransmitters stimulate different organs, have different effects Smooth muscle fibers can sustain longer contraction and use less ATP; also can stretch What sorts of movements are seen in these organs?

  12. Cardiac muscle striated, involuntary muscle Cells are short and branched Calcium channels regulate flux of calcium twitches last longer than in skeletal muscles Intercalated discs connect one cell to another; help with rapid transmission of signals

  13. Entire structure (heart muscle) contracts as a unit Is also self-stimulatory and rhythmic Activity begins in a specific region of the heart and spreads over the entire structure We’ll talk about the pattern and regulation later! Complarison of the 3 types of muscle p. 185

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