The muscular system controls blood flow and pumps blood. Muscle contractions can vary in strength due to the frequency and strength of electrical stimuli. Graded muscle responses depend on the number of motor units activated. Large motor units averaging 1000 muscle cells would be best for lifting heavy objects, while small motor units averaging 14 muscle cells would be best for performing surgery. There are three main types of muscle fibers - slow twitch, fast twitch type IIA, and fast twitch type IIB. Additional studies provide more insight into muscle fiber research and the effects of exercise on fiber type composition.

1. The Muscular System

7. Pump blood (cardiac m.t.)
Control blood flow (smooth m.t.)

19. Freeze-fractured muscle fiber…showing the “broken” myofibrils

34. Graded Muscle Responses
a. Muscle contractions vary in strength due to….
1. Frequency of stimulus

35. 2. Strength of stimulus

37. Ponder this point……..
a. The application of the first stimulus did not activate any motor units.
b. All motor units are active when the “level 6” stimulus was applied.
c. The application of a “level 10” stimulus would result in a stronger contraction than the
“level 7 stimulus.”
d. Indicate which of the following would be best for lifting heavy objects and which
would be best for performing surgery.
_________________ size of motor unit averages 1000 muscle cells
_________________ size of motor unit averages 14 muscle cells

38. Types of Muscle Fibers

39. Slow twitch
muscle fibers
(Type I)

40. Fast twitch (Type II)

41. Type II A
Type II B

43. These studies and journal articles offer more
insight on muscle fiber research:
High-Intensity Training and Changes in Muscle
Fiber
Nature vs. Nurture: Can Exercise Really Alter
Fiber Type Composition?
Effects of Endurance Training on Muscle Fiber