1. 7
The Muscular System

2. ATP and CP Reserves (7-6)
At rest, muscle cells generate ATP, some of which will be held in reserve
Some is used to transfer high energy to creatine forming creatine phosphate (CP)
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3. ATP and CP Reserves (7-6)
During contraction each cross-bridge breaks down ATP into ADP and a phosphate group
CP is then used to recharge ATP
The enzyme creatine phosphokinase (CPK or CK) regulates this reaction
It lasts for about 15 seconds
ATP must then be generated in a different way
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4. Aerobic Metabolism (7-6)
Occurs in the mitochondria
Using ADP, oxygen, phosphate ions, and organic substrates from carbohydrates, lipids, or proteins
Substrates go through the citric acid cycle
A series of chemical reactions that result in energy to make ATP, water, and carbon dioxide
Oxygen supply decides ATP aerobic production
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5. Glycolysis (7-6)
Breaks glucose down to pyruvate in the cytoplasm of the cell
If pyruvate can go through the citric acid cycle with oxygen, it is very efficient
Forming about 34 ATP
With insufficient oxygen, pyruvate yields only 2 ATP
Pyruvate is converted to lactic acid
Potentially causing a pH problem in cells
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6. Figure 7-9 Muscle Metabolism.
Fatty acids G
Blood vessels
Glucose
Glycogen
Mitochondria
Creatine
Resting: Fatty acids are catabolized; the ATP produced
is used to build energy reserves of ATP, CP, and glycogen.
Fatty acids
Glucose
Glycogen 2 2
Pyruvate 34 34
To myofibrils to support
muscle contraction
Moderate activity: Glucose and fatty acids are catabolized;
the ATP produced is used to power contraction.
Lactate
Glucose
Glycogen 2 2
Pyruvate
Creatine
Lactate
To myofibrils to support
muscle contraction
Peak activity: Most ATP is produced through glycolysis,
with lactate and hydrogen ions as by-products. Mitochondrial
activity (not shown) now provides only about one-third of
the ATP consumed.
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7. Figure 7-9a Muscle Metabolism.
Fatty acids G
Blood vessels
Glucose
Glycogen
Mitochondria
Creatine
Resting: Fatty acids are catabolized; the ATP produced
is used to build energy reserves of ATP, CP, and glycogen.
© 2013 Pearson Education, Inc.

8. Figure 7-9b Muscle Metabolism.
Fatty acids
Glucose
Glycogen 2 2
Pyruvate 34 34
To myofibrils to support
muscle contraction
Moderate activity: Glucose and fatty acids are catabolized;
the ATP produced is used to power contraction.
© 2013 Pearson Education, Inc.

9. Figure 7-9c Muscle Metabolism.
Lactate
Glucose
Glycogen 2 2
Pyruvate
Creatine
Lactate
To myofibrils to support
muscle contraction
Peak activity: Most ATP is produced through glycolysis,
with lactate and hydrogen ions as by-products. Mitochondrial
activity (not shown) now provides only about one-third of
the ATP consumed.
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10. Muscle Fatigue (7-6)
Caused by depletion of energy reserves or a lowering of pH
Muscle will no longer contract even if stimulated
Endurance athletes, using aerobic metabolism, can draw on stored glycogen and lipids
Sprinters, functioning anaerobically, deplete CP and ATP rapidly, and build up lactic acid
PLAY
ANIMATION Frog Fatigue
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11. The Recovery Period (7-6)
Requires "repaying" the oxygen debt by continuing to breathe faster
Even after the end of exercise, and recycling lactic acid
Heat production occurs during exercise
Raising the body temperature
Blood vessels in skin will dilate; sweat covers the skin and evaporates
Promoting heat loss
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