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Anatomy Lecture Notes Chapter 11 Chapter 11 - MUSCLES OF THE BODY A. muscles and levers lever = rigid bar that moves on a fixed point fulcrum = fixed point on which lever moves effort = force applied to move resistance load = resistance moved by effort 1. types of levers a. a first class lever has the fulcrum in the middle b. a second class lever has the load in the middle c. a third class lever has the effort in the middle 2. mechanical advantage is determined by the relative lengths of the effort arm and load arm effort x effort arm length = load x load arm length Strong/Fall 2008 page 1 Anatomy Lecture Notes Chapter 11 for a given effort and load: a. when the effort is farther from the fulcrum than the load is, there is a mechanical advantage b. when the effort is closer to the fulcrum than the load is, there is a mechanical disadvantage 3. mechanical advantage [the relative positions of the fulcrum, effort and load] affects: a. amount of weight that can be lifted – the greater the mechanical advantage, the more weight can be moved for the same effort b. speed of contraction c. range of movement 4. skeletal muscles first class second class third class Strong/Fall 2008 page 2 Anatomy Lecture Notes Chapter 11 B. arrangement of fascicles in skeletal muscles 1. types of arrangements: a. parallel - fascicles parallel to axis of muscle b. convergent - fascicles come together at insertion c. pennate - short fascicles attach obliquely to tendon d. circular - fascicles in concentric rings 2. effect of fascicle arrangement on shortening and strength a. degree of shortening depends on fascicle arrangement fibers can shorten about 1/3 of their resting length parallel fascicles shorten the most b. due to cross sectional area (number of muscle fibers) pennate fascicle arrangement has a higher cross sectional area Strong/Fall 2008 page 3 Anatomy Lecture Notes Chapter 11 C. skeletal muscle interactions 1. agonist/prime mover = muscle with major responsibility for producing a movement 2. antagonist = muscle that opposes agonist 3. synergist = help prime movers 4. fixator = synergist that holds a bone in place or stabilizes the origin of the agonist D. criteria for naming skeletal muscles 1 location 2. shape 3. size 4. direction of fascicles 5. location of attachments 6. number of origins 7. action Strong/Fall 2008 page 4