Ch 10.4 Muscle Metabolism

Causes of muscle fatigue

-central fatigue: desire to cease activity is caused by changes in the central nervous system (brain and spinal cord) -it is thought that this response happens to prevent a person from damaging their muscles -inadequate release of calcium ions from the SR = decline of Ca2+ concentration in the sarcoplasm -depletion of creatine phosphate -surprisingly, the ATP levels in fatigued muscle often are not much lower than those in resting muscle -insufficient oxygen -depletion of glycogen -buildup of lactic acid and ADP -failure of action potentials in the motor neuron to release enough ACh

Creatine phosphate

-energy-rich molecule that is found in muscle fibers -relaxed muscle fibers produce more ATP than they need for resting metabolism = excess ATP is used to synthesize ___ ___. -__ ___ is three to six times more plentiful than ATP in the sarcoplasm of a relaxed muscle fiber -first source of energy when muscle contractions begin b/c the formation of ATP from ___ ___ occurs very rapidly with the help of creatine kinase (CK). -ATP and ___ ___ provide enough energy for muscles to contract for 15 seconds

Creatine kinase (CK)

enzyme ___ ___ catalyzes the transfer of one of the high-energy phosphate groups from ATP to creatine, forming creatine phosphate and ADP.

Nutrients available in Aerobic respiration ..

pyruvic acid obtained from the glycolysis of glucose, fatty acids from the breakdown of triglycerides, and amino acids from the breakdown of proteins

Muscle Fatigue

the inability o a muscle to maintain force of contraction after prolonged activity

Oxygen debt

-the added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise -the extra oxygen is used to "pay back" or restore metabolic conditions to the resting level in three ways: 1. to convert lactic acid back into glycogen stores in liver 2. to resynthesize creatine phosphate and ATP in muscle fibers 3. to replace the oxygen removed from myoglobin

3 ways muscle fibers produce ATP

1. creatine phosphate 2. Anaerobic glycolysis 3. Aerobic respiration

Creatine

a small, amino acid-like molecule that is synthesized in the liver, kidneys, and pancreas and then transported to muscle fibers

Myoglobin and hemoglobin

-Both are oxygen-binding proteins -they bind oxygen when it is plentiful and release oxygen when it is scarce

Aerobic respiration

-If sufficient oxygen is present, the pyruvic acid formed by glycolysis enters the mitochondria where it undergoes ___ ___. -this is a series of oxygen-requiring reactions (Krebs cycle & electron transport chain) that produce ATP, CO2, water, and heat. -it is slower than anaerobic glycolysis, but it yields MORE ATP (30 or 32 molecules of ATP) -provides nearly all of the needed ATP in activities that last from several minutes to an hour or more

Glycolysis

-series of reactions that quickly break down each glucose molecule into 2 molecules of PYRUVIC ACID -occurs in the cytosol and produces a net gain of 2 molecules of ATP -Does NOT require oxygen

Anaerobic glycolysis

-the entire process by which the breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration -provides enough energy for 2 minutes of maximal muscle activity -each molecule of glucose catabolized via ___ ___ yields 2 molecules of lactic acid and 2 molecules of ATP -build up of lactic acid in skeletal muscle fibers and bloodstream = soreness -compared to aerobic respiration, ___ ___ produces fewer ATPs, but it is faster and can occur when oxygen levels are low -oxygen not required

2 sources of oxygen for muscular tissue

1. oxygen that diffuses into muscle fibers from the blood (hemoglobin) 2. oxygen released by myoglobin within muscle fibers

oxygen use after exercise is boosted by 3 ongoing changes..

1. the elevated body temp after strenuous exercise increases the rate of chemical reactions throughout the body = faster reactions use ATP more rapidly, and more oxygen is needed to produce the ATP. 2. the heart and the muscles used in breathing are still working harder than they were at rest, so they consume more ATP 3. tissue repair processes are occurring at an increased pace -FOR THESE REASONS "RECOVERY OXYGEN UPTAKE" IS A BETTER TERM THAN "OXYGEN DEBT" FOR THE ELEVATED USE OF OXYGEN AFTER EXERCISE

1. During exercise 2. After exercise

Metabolic changes that occur __(1)__ can account for only some of the extra oxygen used __(2)__ .

Lactic acid

Under anaerobic conditions, the pyruvic acid generated from glycolysis is converted to __ ___.

Anaerobic glycolysis and aerobic respiration

_____ & _____ take a relatively longer period of time to produce ATP compared to creatine phosphate

1. Glucose 2. ATP

when muscle activity continues and the supply of creatine phosphate within the muscle fiber is depleted , __(1)_ is catabolized to generate _(2)__