Energy sources of muscle contractions

1. Chapter 9, Section 4
Energy Sources for Contraction

2. Energy Sources for Contraction
ATP provides the energy to power the interaction
between actin & myosin filaments.
• However, ATP is quickly spent and must be
replenished
New ATP molecules are synthesized by
1. Hydrolysis of Creatine Phosphate
2. Glycolysis (anaerobic respiration)
3. Aerobic Respiration

3. Creatine Phosphate
Creatine Phosphate can be hydrolyzed into Creatine, releasing
energy that is used to make new ATP.
The energy from creatine phosphate hydrolysis cannot be used
to directly power muscles.
Instead, it’s used to produce new ATP.

4. Creatine Phosphate…continued
When cellular ATP is abundant, creatine phosphate can
be replenished by phosphorylating creatine.
Creatine Phosphate provides energy for only about 10
seconds of a high intensity muscle contraction.

5. Glycolysis
Anaerobic respiration (glycolysis) occurs in the cytosol of the cell
and does not require oxygen.
Glucose molecules are partially broken down producing just 2 ATP
for each glucose.
If there isn’t sufficient oxygen available, glycolysis produces lactic
acid as a byproduct.

6. Oxygen debt of glycolysis
Exercise and strenuous activity depends on
anaerobic respiration for ATP supplies.
During exercise anaerobic respiration causes
lactic acid to accumulate in the cells.
After exercise, when oxygen is available
the O2 is used to convert lactic acid back to
glucose in the liver.
Oxygen debt is the amount of oxygen
needed by liver cells to convert
accumulated lactic acid back to glucose.

7. Oxygen debt

8. Aerobic Respiration
Aerobic respiration (uses oxygen) occurs in the mitochondria and it
includes the citric acid cycle & electron transport chain.
Aerobic respiration is a slower reaction than glycolysis, but it produces
the most ATP.
Myoglobin
Oxygen binding protein (similar to hemoglobin) within muscles
-Provides additional oxygen supply to muscles

9. Aerobic Respiration
Aerobic respiration is used primarily at rest or during
light exercise.
Muscles that rely on aerobic respiration have plenty of
mitochondria and a good blood supply.

10. Energy Sources for Contraction
Figure 9.13. The oxygen required for aerobic respiration is
carried in the blood and stored in myoglobin. In the absence of
oxygen, anaerobic respiration uses pyruvic acid to produce lactic
acid.

11. Muscle Fatigue
• Muscle Fatigue = Inability for the muscle to contract
• Several factors can cause muscle fatigue:
• Decreased blood flow
• Ion imbalances across the sarcolemma
• Lactic acid accumulation – (greatest cause of fatigue)
• Cramp:
• A cramp is a sustained, involuntary, and painful muscle
contraction
• It’s due to electrolyte imbalance surrounding muscle

12. Heat Production
• Heat is produced as a by-product of cellular respiration
• Muscle cells are major source of body heat
• Blood transports heat throughout body core
End of Chapter 9, Section