Transcript muscle3
Abstract due Monday At start of class. Abstract Reviewers Schedule Thursday, Oct 25 Friday, Oct 26 Saturday Afternoon, Oct 27 Sunday, Oct 28 in Acorn Cafe by appointment 1-2 pm Biology Office 12- 2 with Miranda Stockman 9-11 am Biology with Polly Suite 2-4 with Polly Ketcham Office Suite Ketcham Miranda Stockman 4-6 with Brooks Owens with Sharon Guffy ketchampd@em and Brooks Owens 6-8 with Becca Bryson ail.wofford.edu 1QQ # 19 for 10:30 Convert to a correct statement or if true, write true. 1. Skeletal myofibers have muscarinic acetylcholine receptors. 2. Skeletal myofibers have adrenergic receptors, but the binding of EPI does not cause contraction. 3. After a powerstroke, ATP must bind to the myosin head before the crossbridge can detach from actin. 4. The duration of a muscle twitch depends on how rapidly Ca++ is actively transported back into the Ttubule. 5. A drug that activates ryanodine receptors would cause a skeletal muscle to contract. 1QQ # 19 for 11:30 Convert to a correct statement or if true, write true. 1. Skeletal myofibers have muscarinic acetylcholine receptors. 2. Skeletal myofibers have adrenergic receptors, but the binding of EPI does not cause contraction. 3. After a powerstroke, ATP must bind to the myosin head before the crossbridge can detach from actin. 4. The duration of a muscle twitch depends on how rapidly Ca++ is actively transported back into the Ttubule. 5. There are two isozymes of actin which hydrolyze ATP at different rates. S7 3 Sources of ATP in muscle Powerstroking & Disconnecting crossbridges Creatine phosphate, then oxidative phosphorylation (OP) from glycogen, then OP from blood glucose, then blood fatty acids. If intense, switch to glycolysis… then take a breather… oxygen debt S8 Would creatine supplementation benefit endurance runners? Muscle Fatigue Central Fatigue • Psychological drive • Protective reflexes – Chemoreceptors in muscles? Many factors are associated with muscle fatigue. Factors that cause muscle fatigue are still uncertain. Peripheral Fatigue • • • • • • • Less ACh release Less AChR activation AP conduction failure in T-tubles Leaking Ca++ from SR Less Ca++ released from SR Disturbed Ca++ binding to Troponin Depletion Hypotheses – Depletion of phosphocreatine – Depletion of ATP – Depletion of glycogen • Accumulation Hypotheses – Accum of H+ – Accum of inorganic phosphate – Accum of lactate S5 Classes of Myofibers based on Twitch Duration Each muscle fiber express only one of two different myosin isozymes: • Fast twitch = rapid hydrolysis of ATP means crossbridges cycle faster • Slow twitch = slower hydrolysis, isozyme catalyzes the reaction slower Myosin Isozymes not modified by athletic training but metabolic pathway enzymes are! Contraction velocity also affected by load! S 10 Skeletal Myofiber Types Character Type I (Slow Ox) Type II A (FOG) Type II B (FG) slow fast fast Metabolism Oxidative (aerobic) oxidative & glycolytic glycolytic Ca++ ATPase moderate fast Fast Mitochondria numerous moderate Few small medium Large Dark red (myoglobin) red pale Capillary density high moderate Low Recruitment first second third Fatigue resistant Fatigue resistant Easily fatigued Most used. posture Walking, standing Least used: jumping, quick fine movements Myosin ATPase Myofiber diameter Color Endurance Usage Duck Chicken Muscles (the organs) consist of various proportions of all three myofiber types depending on the usage of that muscle. Tour de France Running from Saturday June 29th to Sunday July 21th 2013, the 100th Tour de France will be made up of 21 stages and will cover a total distance of 3,479 kilometres (before ratification). These stages have the following profiles: 7 flat stages 5 hilly stages 6 mountain stages with 4 summit finishes 2 individual time trial stages 1 team time trial stage 2 rest days Skeletal Myofiber Types Character Type I (Slow Ox) Type II A (FOG) Type II B (FG) slow fast fast Metabolism Oxidative (aerobic) oxidative & glycolytic glycolytic Ca++ ATPase moderate fast Fast Mitochondria numerous moderate Few small medium Large Dark red (myoglobin) red pale Capillary density high moderate Low Recruitment first second third Fatigue resistant Fatigue resistant Easily fatigued Most used. posture Walking, standing Least used: jumping, quick fine movements Myosin ATPase Myofiber diameter Color Endurance Usage S7 Response to training • Resistance training Type II change enzyme profiles: II A to II B Type II add more actin and myosin Type II increase cross-sectional area (hypertrophy) • Endurance training – Type I increases vascularity – Type I increase number of mitochondria S8 Read section of King et al., 1999 that deals with analysis of muscle biopsy material in subjects taking Andro or placebo while resistance training. What changes were expected? What changes were observed? Fig. 09.24b S 14 Fig. 09.13 Motor unit = a single somatic motor neuron and all the muscle fibers in innervates S 15 But each motor unit has myofibers of the same type: I or IIA or IIB. S 17 Fig. 09.26 Relationship between recruitment and motor unit type The Size Principle Size of somatic motoneuron cell body