Cellular Respiration in Muscles Cellular Respiration supplies the ATP(Adenosine Triphosphate) or useful cellular energy needed for cells to do the things which require energy. Muscles need very large amounts of ATP/sec when they are contracting. For ALL Human Cells: Cellular or Aerobic Respiration provides energy in the form cells can use (ATP) and therefore occurs in every cell of the body. (The first part of cellular or aerobic respiration is in the Cytoplasm but most of the energy is released in the mitochondria) Aerobic indicates that Oxygen(air) is required. Raw materials for cellular respiration: Glucose or some other food molecule provides the chemical bond energy needed to make ATP from ADP and P. Oxygen is an additional raw material although it does not supply any of the chemical bond energy for making ATP. Waste Materials of Cellular respiration (What remains of the Glucose and 0 2 when Glucose's chemical bonds have been broken to produce as much ATP as possible): C0 2 and H20 What desirable product Is produced as a result of the glucose being dismembered by the enzymes of the cytoplasm and mitochondria? 36 new ATP are formed from 36 ADP + 36 P using the glucose or food's chemical bond energy to supply the energy to synthesize or produce the 36 ATP. (Some cells produce 38 ATP/glucose so either number is acceptable.) To supply its energy needs, every cell of the human body, breaks down glucose (or other food molecules) one step at a time using the enzymes in the cytoplasm. Enough energy is released from the glucose to put 2ADP + 2P together to form 2ATP, using the enzymes of the cytoplasm. After this energy is released, the glucose has been changed to 2 smaller molecules about half the size of glucose called pyruvic acid, which still contains most of glucose's energy. If 02 is available in the cell (and the cell is working normally), each of the pyruvic acid molecules is changed by an enzyme and to a smaller molecule which can be broken down in the mitochondria. These 2 molecules (the remains of the glucose) still possesses most of the energy of the original glucose. These 2 pyruvic acid molecules will be totally torn apart by the enzymes (Krebs Cycle) contained in the mitochondria, leaving only C0 2 and the H of the glucose will be combined with 0 of the air to form H20. The energy from the molecules (undergoes oxidative phosphorylation) is used to put 34 more ADP together with 34P to form 34 new ATP. These 34 ATP from the mitochondria + 2 ATP from the break down in the cytoplasm mean that 36 new ATP are produced for each glucose reduced to 6 C0 2 and 6 H20 --providing oxygen is available). This is a good mechanism for producing ATP but It Is slow and requires 0 2 (which may get used up quickly if the cell is very active.) Because ATP is used much more slowly in most human cells, cells only have a limited supply of ATP. There is only enough ATP to last a contracting muscle cell for 4-6 seconds.
Active Muscle cells need SO MUCH ATP, they have unusual adaptations: 1) Myoglobin, a protein similar to Hemoglobin which carries 02 in the Red Blood Cells for the blood, stockpiles extra oxygen In muscle cells so muscle cells have extra 0 2 for making ATP when they are active. 2) Creatine Phosphate, CP, stores an extra high energy phosphate which can be directly transferred to ADP to make ATP when needed. Muscle cells store enough CP to produce ATP for another 15·20 sec. (Also Unique to muscles.) 3) Skeletal Muscles and the liver are the only locations in the body where glycogen is stored. Glycogen is a polysaccharide made of glucose which can provide the many glucose needed for muscle contraction should an emergency present itself (Fight or Flight.) 4) Skeletal Muscles have an additional emergency back up enzyme that is not found in ANY other human cell. This enzyme can change pyruvic acid to lactic acid. This enzyme can only be used when 02 has been exhausted from the muscle cell. Since the break down of glucose in the cytoplasm using this enzyme does not require air or oxygen, it Is called ANAEROBIC RESPIRATION or lactic Acid Fermentation. Advantage of Anaerobic Respiration (also known as Lactic Acid Fermentation): 1) Anaerobic Respiration can continue producing 2 ATP/glucose for muscle cell use, even when 0 2 Is absent. (The mitochondria is useless so only the cytoplasmic enzymes can work.) 2) Anaerobic Respiration is 21/2 times faster than aerobic respiration in the mitochondria but uses a lot of glucose and produces LOTS of lactic ACID-a problem. 3) Anaerobic Respiration can supply another 30-60 sec of ATP for strenuous muscle activity. Disadvantage of Anaerobic Respiration: 1) Anaerobic Respiration uses up tremendous amounts of glucose because it produces such a small amount of ATP (2ATP/glucose compared to the 36 ATP/glucose that aerobic respiration produces) therefore If using lots of ATP, tremendous amounts of glucose needs to be changed to lactic aCid.]. 2) Anaerobic Respiration produces Lactic Acid which lowers the pH of the muscle cells and messes up homeostasis in muscle cells. Lactic Acid makes the muscle cells SORE and promotes Muscle Fatigue. Muscle Fatigue, an inability of a muscle to contract when It is being stimUlated, is due to Oxygen debt. ( as well as an increase In lactic acid.) Muscle soreness or fatigue will decrease when circulation of blood increases bringing more oxygen to. the muscle cell. Among the things that can be done to Increase circulation of blood to an area which has sore muscles are the following: 1) Stretching or mild exercise Improves the circulation to the area stretched 2) Warmth to the area (hot shower or bath) improves circulation & decreases soreness. 3) Icy Hot or Ben Gay are substances which relax the smooth muscles around the blood vessels (arteries and arterioles) in the affected area, therefore Improving circulation and allowing more oxygen to the area. The Increased circulation also delivers more lactic acid to liver (removing it from muscles) to be changed back to glucose.