Download Ch 6 Whole Muscle Contraction

Pages 187-195

Muscle fiber contraction is “all or none”
◦ There is no “in-between” contraction
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
Not all fibers may be stimulated at one time
Different combinations of muscle fiber
contractions may give differing responses
◦ Graded responses= different degrees of skeletal
muscle shortening
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
Graded responses can be produced by
changing:
◦ The frequency of muscle stimulation
◦ The number of muscle cells being stimulated (and
therefore, recruited) at one time

more fibers= greater muscle tension
◦ Muscles can contract until they run out of energy
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
Adenosine Triphosphate (ATP)
◦ Immediate source
◦ Stored in muscle fibers in small amounts that are
quickly used up
 After this initial time, other pathways must be utilized
to produce ATP
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1.
Direct phosphorylation of ADP
◦
by creatine phosphate
2.
Aerobic (cellular) respiration (most ATP)
3.
Anaerobic (cellular) respiration
◦
glycolysis and lactic acid formation
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
Muscle cells store CP, a high-energy molecule
◦ After ATP is depleted, ADP remains
◦ CP transfers a phosphate group to ADP to
regenerate ATP
◦ CP supplies are used up in less than 15 seconds
 (About 1 ATP is created per CP molecule)
 *creatine phosphate is also known as phosphocreatine
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Figure 6.10a Methods of regenerating ATP during muscle activity.
(a) Direct phosphorylation
Coupled reaction of creatine
phosphate (CP) and ADP
Energy source: CP
CP
Creatine
ADP
ATP
Oxygen use: None
Products: 1 ATP per CP,
creatine
Duration of energy provision:
15 seconds
–
breaks down glucose without oxygen
– broken down to pyruvic acid, then to lactic acid
– produces about 2 ATP very quickly
– Lactic acid accumulates in the muscles and
produces fatigue
–
After exercise, the oxygen deficit is repaid by
rapid, deep breathing
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Figure 6.10b Methods of regenerating ATP during muscle activity.
(b) Anaerobic pathway
Glycolysis and lactic acid
formation
Energy source: glucose
Glucose (from
glycogen breakdown or
delivered from blood)
Glycolysis
in cytosol
O2
2 ATP
net gain
Released
to blood
Pyruvic acid
O2
Lactic acid
Oxygen use: None
Products: 2 ATP per glucose,
lactic acid
Duration of energy provision:
40 seconds, or slightly more

Glucose is broken down to CO2 and H2O
◦
◦
◦
◦
Creates about 32 ATP per glucose molecule
occurs in the mitochondria
slower reaction, requires continuous oxygen
Provides hours of sustained energy
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See page 194 for this side-by-side comparison of pathways
Comparison of pathways
Image source:http://www.udel.edu/chem/C465/senior/fall00/Performance1/phosphocreatine.htm.html
•
Isotonic contractions
– Myofilaments slide past each other during
contractions
– The muscle shortens, and movement occurs
– Example: bending the knee; rotating the arm
•
Isometric contractions
– Tension in the muscles increases
– The muscle doesn’t shorten or produce movement
– Example: pushing against a wall with bent elbows
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
Increase in muscle:
◦
◦
◦
◦
Size
Strength
Endurance
Aerobic (endurance) exercise=
 stronger
 more flexible muscles
 greater resistance to fatigue
◦ Resistance, or isometric, exercise like weight lifting
increases muscle size and strength
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