Muscle & Movement PHSL 3051 Spring 2024 PDF

Muscle & Movement PHSL 3051 Dr. Barnett Energy Metabolism and Muscle Fiber Types Class 12 Learning Objectives Class 12: Molecular Mechanisms of Contraction and Metabolism Derrickson (1st edition: p. 383-393, 2nd edition: p 394-407) 1. List the energy sources for muscle contr...

Muscle & Movement PHSL 3051 Dr. Barnett Energy Metabolism and Muscle Fiber Types Class 12 Learning Objectives Class 12: Molecular Mechanisms of Contraction and Metabolism Derrickson (1st edition: p. 383-393, 2nd edition: p 394-407) 1. List the energy sources for muscle contraction and rank the sources with respect to their relative speed and capacity to supply ATP for contraction. 2. Construct a table of structural, enzymatic, and functional features of fast- glycolytic, fast-oxidative, and slow-oxidative fiber types from skeletal muscle. 3. List the factors that can contribute to muscle fatigue and describe basis of the differences in fatigue resistance in different muscle fiber types. 4. Define a motor unit and describe the order of recruitment of motor units during skeletal muscle contractions producing low, moderate and high amounts of tension. 5. List the factors that determine the tension developed in a whole muscle and explain how each contributes to the amount of tension generated. 2 3 ATP Production in Skeletal Muscle H2N N ATP N N N O O O O -O O O P O P P O- O- O- Kinases OH OH Myosin ATPase Glycolysis Adenosine Triphosphate Ca2+-ATPase Oxidative Phosphorylation Na+/K+-ATPase H2N O Phosphate N -O P O- N O- Energy Energy N N O O O -O P O P O ADP For cellular From food O- O- Sugars OH OH work Fats Proteins Adenosine Diphosphate  ATP production in skeletal muscle 1. Creatine Kinase  One step reaction  Transfers phosphate from Creatine-phosphate to ADP to regenerate ATP 2. Glycolysis 2  Multistep reaction 1 Creatine Kinase  Anaerobic  Converts 1 Glucose to 2 ATP 3. Oxidative 3 Phosphorylation  Multistep reaction  Requires Oxygen (O2) and mitochondria  Converts 1 Glucose to 36 ATP  Converts Fatty acids to ATP  Converts Amino acids to ATP 4 ATP production in skeletal muscle 1. Creatine Kinase (CK)  One step reaction  Transfers phosphate from Creatine Creatine phosphate (CP) to ADP to regenerate ADP ATP phosphate CP provides a “reservoir” of high energy phosphate which is accumulated during rest in muscle cells* Creatine Kinase CK provides ATP during first few seconds of a contraction The ATP production is rapid, but limited ATP Creatine by the amount of CP stored in cell Powers very short periods of muscle activity *Glycolysis and/or oxidative phosphorylation during periods of rest can regenerate Creatine Phosphate from ATP and Creatine because the Creatine Kinase enzyme can run in reverse! 5  ATP production in skeletal muscle 2. Glycolysis Muscle glycogen  Multistep reaction (slow)  Anaerobic Converts 1 Glucose to 2 ATP  Blood Anaerobic: Glucose Glucose Can produce ATP from glucose in the absence of O2 Glycolysis Kicks in during high intensity exercise In the presence of large amounts of 2 Lactic acid 2 Pyruvic acid glucose, can produce large quantities of ATP Insufficient O2 Glucose can come from blood or available from breakdown of muscle glycogen Powers short periods of muscle ATP activity O2 available Oxidative Phosphorylation 6  ATP production in skeletal muscle Glycolysis 3. Oxidative Phosphorylation  Multistep reaction (slow) Pyruvic acid  Requires Oxygen (O2) and mitochondria Blood Sufficient O2  Converts 1 Glucose to 36 ATP available ATP  Converts Fatty acids to ATP  Converts Amino acids to ATP Phosphorylation of ADP occurs Aerobic Respiration Mitochondrion in mitochondria O2 Multi-enzyme pathway that requires O2 Fatty Kreb’s Cycle Initially (first 5-10 min. of acids activity), glycogen is the major fuel Amino Next 30 min, blood borne acids glucose and fatty acids CO2 H2O contribute fuel, eventually giving way to mostly fatty acids Powers extended periods of muscle activity 7  ATP production in skeletal muscle 1. Creatine Kinase (CK)  One step reaction  Transfers phosphate from Creatine phosphate (CP) to ADP to regenerate ATP CP is a “storehouse” of high energy phosphate which is 2 accumulated during rest in 1 Creatine Kinase muscle cells CK provides ATP during first few seconds of a contraction 3 The ATP production is rapid, but limited by the amount of CP stored in cell Powers very short periods of muscle activity The enzymatic action of CK is reversible! During periods of rest, CK transfers a phosphate from ATP to creatine to regenerate the reserves of creatine phosphate. 8  ATP production in skeletal muscle 2. Glycolysis  Multistep reaction (slow)  Anaerobic (low O2)  Converts 1 Glucose to 2 ATP Anaerobic: can produce ATP from glucose in the absence of O2 2 Kicks in during high intensity 1 Creatine Kinase exercise In the presence of large amounts of glucose, can produce large 3 quantities of ATP Glucose can come from circulatory system or from the breakdown of muscle glycogen Powers short periods of muscle activity 9  ATP production in skeletal muscle 3. Oxidative Phosphorylation  Multistep reaction (slow)  Requires Oxygen (O2) and mitochondria  Converts 1 Glucose to 36 ATP  Converts Fatty acids to ATP  Converts Amino acids to ATP 2 Phosphorylation of ADP occurs in mitochondria 1 Creatine Kinase Multi-enzyme pathway that requires O2 3 Initially (first 5-10 min. of activity), glycogen is the major fuel Next 30 min, blood borne glucose and fatty acids contribute fuel, eventually giving way to mostly fatty acids Powers extended periods of muscle activity 10 Energetics Question Which ATP backup system is found in all skeletal muscles? 1. Glycolysis 2. Oxidative Phosphorylation 3. Creatine Kinase Muscle Fiber Types Classified according to: maximal velocity of shortening (i.e. how quickly myosin can hydrolyze ATP) major pathway they use to form ATP Red muscle, small diameter cells 1. Slow-oxidative - Slow myosin aerobic metabolism Red muscle, intermediate diameter cells 2. Fast-oxidative - Fast myosin, aerobic and anaerobic metabolism - White muscle, large diameter cells 3. Fast-glycolytic - anaerobic metabolism 12  Muscle Fiber Types (really a continuum, but it is helpful to compare and contrast 3 general scenarios): 1. Slow-oxidative fibers - small diameter = less tension - slow myosin so tension development is slow - mostly oxidative phosphorylation which requires O2 - many mitochondria and many capillaries to provide O2 - large amounts of myoglobin to aid in O2 diffusion and to store O2 (dark meat) - resistant to fatigue - e.g. postural muscles 13  Muscle Fiber Types 2. Fast-oxidative fibers - larger diameter = more tension - fast myosin ATPase so tension development is faster - mostly oxidative phosphorylation which requires O2 - many mitochondria and capillaries to provide O2 - large amounts of myoglobin to aid in O2 diffusion and to store O2 (dark meat) – less myoglobin than slow-oxidative muscle - somewhat resistant to fatigue 1. Slow-oxidative 2. Fast-oxidative 14  Muscle Fiber Types 3. Fast-glycolytic fibers - larger diameter = more tension - fast myosin ATPase so tension development is fast - mostly glycolytic metabolism (does not depend on O2) - large amounts of glycogen to provide fuel for glycolysis - fewer capillaries and mitochondria - essentially no myoglobin (white meat) - prone to fatigue 1. Slow-oxidative 2. Fast-oxidative 3. Fast-glycolytic 15 Muscle Fiber Types Muscles are tuned to activities based on their anatomical location and their metabolic properties 16  Motor Units A motor unit is defined as a motor neuron and the population of muscle fibers it innervates. Two motor units can generate more tension than one. When a large amount of tension needs to be generated, more motor neurons (and hence muscle fibers) are recruited. 17 What is the mechanism of Fatigue? Time What is the mechanism of fatigue? Don’t really know, but … 1 - NOT absence of ATP – or else there would be rigor 2 - High extracellular K+ concentration 3 - Lactic acid – disproven 4 – Build-up of ADP – inhibition of crossbridge cycling 5 – disruption of calcium regulation, possibly by malfunctioning Ca2+channels on the SR 18 Fatigability of skeletal muscles Slow oxidative: - slow myosin ATPase - least amount of tension - least likely to fatigue Fast oxidative: - fast myosin ATPase - moderate amount of tension - moderately likely to fatigue Fast glycolytic: - fast myosin ATPase - greatest amount of tension - most likely to fatigue rapidly 19 What factors could affect how much tension a whole muscle can produce? relaxed ? active ? 1. The number of active motor units 2. The number of muscle fibers in each motor unit 3. The fiber types of the activated motor units 20  Recruitment Increasing load Increasing muscle force required Large motor units Small motor units Medium motor units Increasing motor unit size Based on Figure 11.17 21  Recruitment Motor unit 1: slow-oxidative fibers Motor unit 1: slow oxidative - small diameter muscle fibers - few fibers per motor unit - generates least tension Motor unit 2: fast-oxidative fibers Motor unit 3: fast-glycolytic fibers Motor unit 2: fast oxidative - midsized muscle fibers - moderate # of fibers per motor unit Whole-muscle tension - generates moderate tension Motor unit 3: fast glycolytic - large muscle fibers - many fibers per motor unit - generates most tension, quickly Time Motor unit Motor unit Motor unit 1 recruited 2 recruited 3 recruited 22 Muscle Recruitment Question To complete this lift the athlete must recruit: 1. A. Slow twitch muscles only 2. B. Fast twitch muscles only 3. C. All muscles available