Muscle Function and Contraction Notes

Motor Units

• Comprised of one motor neuron and all muscle fibers it innervates.
• Motor units contract when the motor neuron fires.
• Multiple motor units can work together to maintain tension in muscles and avoid fatigue.

Muscle Contractions

• Isotonic Contractions: Muscle changes in length.
• Concentric: Muscle shortens (e.g., lifting a weight).
• Eccentric: Muscle lengthens (e.g., slowly lowering a weight).
• Isometric Contractions: Muscle length does not change (e.g., pushing against an immovable object).
• Useful in rehabilitation to strengthen muscles without aggravating injury.

Muscle Activity

• At rest: Oxygen, glucose, and fatty acids are available; ATP is initiated through aerobic processes.
• Excess ATP is stored as creatine phosphate for later use.
• Moderate activity: Stored glycogen is used for ATP, oxygen is present, and fatty acids can be utilized.
• Creatine phosphate is not used significantly in this phase.
• Peak activity: Oxygen may not be available; glycolysis occurs, resulting in lactic acid production and fatigue.
• Lactic acid can be converted back to glucose via gluconeogenesis in the liver.

ATP in Muscle Contraction

• Essential for releasing myosin heads from actin during muscle contraction.
• Continuous ATP production is important during activity, especially in high-intensity scenarios.

Chemistry of Muscle Activity

• Glycolysis, citric acid cycle, and electron transport chain are key processes in ATP generation.
• Glycolysis does not require oxygen, while the latter two do.

Cori Cycle: Lactic acid converted back to glucose in the liver to manage acid buildup during anaerobic activity.

• Important for maintaining pH balance in the body.