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Energy for Muscle Contraction • Must have constant supply of ATP for contraction to be maintained. • Creatine phosphate (CP) can also be used b/c of its high energy bond. • Cellular respiration or catabolism of food generates more ATP or CP. • Some muscle fibers ensure an uninterrupted supply of glucose by storing it as glycogen. • • • • • Providing Energy for Muscle Contraction Direct phosphorylation of ADP by reaction with creatine phosphate Energy Source: CP Oxygen Use: None 1 ATP per CP Creatine and ATP are the products NRG supply lasts 15 sec Providing Energy for Muscle Contraction • Anaerobic glycolysis and lactic acid formation – Anaerobic- without oxygen • 2 ATP • Lactic acid accumulation (eventually reconverted to glucose in the liver) • Heavy breathing helps to restore oxygen debt. • • • • Energy source is glucose No oxygen is used 2 ATP per glucose, lactic acid 30-60 sec. worth of energy Providing Energy for Muscle Contraction • Aerobic Respiration/Oxidative Phosphorylation – Aerobic- with oxygen • 36-38 ATP • Myoglobin pigment in muscles holds oxygen when muscles are at rest (muscles with much myoglobin are called red fibers; white fibers do not have much myoglobin). Energy Systems used during contraction VI. All-or-none Priciple 1. Muscle cells do not partially contract. They either do or they do not. 2. The minimum level of stimulation required to cause a fiber to contract is the threshold stimulus. Muscle Twitch Response of a muscle to a single brief threshold 1. Latent Period: few ms between stim. & contrac. coupling 2. Contraction: cross-bridges active 3. Relaxation: begins with Ca2+ moving into SR Wave summation • Muscle responds to the frequency and strength of simulation Muscle Contractions • Isotonic: Moving montraction Muscle Contraction • Isometric: Myofilaments are skidding instead of sliding and the tension in the muscle keeps increasing Exercise • Endurance: Aerobic – Stronger, flexible muscles – Greater resistance to fatigue – Increase in blood supply – Fibers form more mitochondria – Store more oxygen Exercise • Resistance or Isometric Exercise – Increased muscle size – Increase strength – Enlargement of individual fibers – More mitochondria Muscle Fatigue and Oxygen Debt • • • • Muscle fatigue: unable to contract May result from oxygen debt Oxygen Debt must be paid back Rapid breathing: continues until the amount of oxygen needed to get rid of the accumulated lactic acid by making ATP and creatine reserves • Before a skeletal muscle fiber can contract, it has to receive an impulse from a nerve cell. • Generally, an artery and at least one vein accompany each nerve that penetrates the epimysium of a skeletal muscle. • Branches of the nerve and blood vessels follow the connective tissue components of the muscle of a nerve cell and with one or more minute blood vessels called capillaries.