Download Chapter 11 - MUSCLES OF THE BODY

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
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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
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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
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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
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