Energy for Muscle Contractions Anatomy & Physiology Chapter 6

Energy for Muscle Contractions Your muscles have various ways of providing the energy necessary to perform a muscle contraction. 4 possible ways to meet the energy needs of a muscle follow:

Plan A: Immediate and direct source is on-site ATP molecules. – Fibers contain enough ATP to sustain contractions for 5-6 seconds Chemical equation = – ATP  ADP + phosphate + energy

Plan A: On-site ATP Involves breakdown of stored glycogen to glucose into pyruvate, which is then converted to lactic acid. However, if lactic acid accumulates, fatigue results

Plan B: Creatine Phosphate – This is a high energy compound used to produce ATP – Provides for about 15 seconds of maximal contraction Chemical equation = – Creatine phosphate  creatine + phosphate + energy – The energy created here is used to convert ADP + phosphate  ATP

Plan C: Glycogen – On-site ATP and creatine phosphates have been exhausted. – Stored glycogen  ATP (thru glycolysis) – Anaerobic process good for another seconds of maximum muscular contractions – Can go to aerobic respiration if enough oxygen is available (provides for even longer period of contractions)

Plan C: Glycogen – Cellular Resp. Pyruvate turned into acetyl CoA, which then enters Kreb’s cycle. – complete breakdown of the glucose molecule. Provides 20x more ATP than anaerobic respiration – Useful during endurance exercise BUT… Anaerobic is 2.5x faster than aerobic Note: Activities requiring sudden surges of power (tennis, soccer) use aerobic + anaerobic

Plan D: Alternate Metabolic Pathways – As exercise intensity increases, and glycogen stores are depleted, alternate sources are converted to glucose (gluconeogenesis) – Must be enough oxygen available to switch to these sources (aerobic) Start to metabolize lipids Start to metabolize proteins

Aerobic vs. Anaerobic Aerobic means "with oxygen." Aerobic exercise is any large muscle activity that you can sustain for two to three minutes or longer, because exercising for prolonged periods requires a source of oxygen and its delivery to the muscles. Because aerobic exercise requires oxygen from the air to get to your muscles, the exercise can continue only when a source of oxygen is available. Your heart and lungs work together to supply oxygen to tissues in your body.

Aerobic vs. Anaerobic The term "anaerobic" means "without air" or "without oxygen." Anaerobic exercise uses muscles at high intensity and a high rate of work for a short period of time. Anaerobic exercise helps us increase our muscle strength and stay ready for quick bursts of speed.

Homeostasis of Muscle Tissues How do your muscle maintain homeostasis?

Oxygen Debt Occurs when muscular exertion is so great that the cardiovasular system can not meet the muscle fibers oxygen needs. – Anaerobic glycolysis produces the ATP – Lactic acid is then produced when not enough O2 is available

Oxygen Debt Example: – You run the 100 meter dash in 12 seconds. This exercise requires 6 liters of oxygen for total aerobic respiration. Actual oxygen that can be delivered to muscles is only 1.2 liters. You now have an oxygen debt of 4.8 liters.

Paying back the Debt Involves: – Converting lactic acid back into pyruvic acid (80% of this occurs in the liver – causing an increase in blood pH) – Replenishing ATP in muscle fiber – Replenishing creatine phosphate – Payback of oxygen borrowed from: Hemoglobin Myoglobin Oxygen in lungs and other body fluids

Maximal Oxygen Uptake The maximum capacity for oxygen consumption by the body during maximum exertion. OR “How much oxygen your body can take in during exercise lasting over 1 minute.”