skeletal muscle metabolism and fiber types
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بسم الله الرحمن الرحيم. Skeletal Muscle Metabolism and Fiber Types. Dr.Mohammed Sharique Ahmed Quadri Assistant Professor, Physiology. Contraction-Relaxation Steps Requires ATP muscle has been called "a machine for converting chemical energy into mechanical work.". - PowerPoint PPT PresentationTRANSCRIPT
Skeletal Muscle Metabolismand Fiber Types
Dr.Mohammed Sharique Ahmed QuadriAssistant Professor, Physiology
بسم الله الرحمن الرحيم
Contraction-Relaxation Steps Requires ATP
muscle has been called "a machine for converting chemical energy into mechanical
work."
Contraction-Relaxation Steps Requiring ATP
• Splitting of ATP by myosin ATPase provides energy for power stroke of cross bridge
• Binding of fresh molecule of ATP to myosin lets bridge detach from actin filament at end of power stroke so cycle can be repeated
• Active transport of Ca2+ back into sarcoplasmic reticulum during relaxation depends on energy derived from breakdown of ATP
Energy Sources for Contraction
• Transfer of high-energy phosphate from creatine phosphate to ADP
• Oxidative phosphorylation (citric acid cycle and electron transport system
• Glycolysis
CREATINE PHOSPHATE
creatine kinaseCreatine phosphate + ADP creatine + ATP
• First source for supplying additional ATP when exercise begins .
• First few minute or less of exercise • Supports short burst of high intensity contractile
efforts• source of creatine in diet , MEAT
Oxidative phosphorylation
• In muscle mitochondria if sufficient O2 is present
• Relatively slow – many steps involved
• Supports aerobic ( with O2) or endurance-type exercise
• Adequate O2 & nutrients required
• Fueled by glucose or fatty acids depending upon intensity and duration of activity• Rest / light exercise – Fatty acids • High intensity exercise – Glucose
Glycolysis
• When O2 delivery or Oxidative phosphorylation can not keep pace with the demand for ATP
• Advantage • Produce ATP in absence of O2• Much faster than oxidative phosphorylation
• Supports anaerobic or high-intensity exercise• Disadvantage • Depletion of nutrient /energy reserve• Production of lactate
FATIGUE• Contractile activity in a muscle can not be
maintained at given level indefinitely
• Fatigue – Muscle fatigue – Central fatigue
Muscle Fatigue• Exercising muscle can no longer respond to
stimulation with same degree of contraction • Defense mechanism that protects muscle from
reaching - (rigor mortis)
• Underlying causes of muscle fatigue are unclear• Local increase in ADP & inorganic phosphate• Accumulation of lactate• Accumulation of extracellular K+
• Depletion of glycogen energy reserve
Central Fatigue
• Occurs when CNS no longer adequately activates motor neurons supplying working muscles
• Often psychologically based
• Mechanisms involved in central fatigue are poorly understood
Neuromuscular fatigue: inability of motor neuron to synthesize acetylcholine- possible only experimentally
The Oxygen Debt Mechanism
• After a period of exertion is over, extra O2 is consumed to
• Remove the excess lactate
• Replenish the ATP and phosphorylcreatine stores
• Replace the small amounts of O2 that have come from myoglobin.
Major Types of Muscle Fibers
• Classified based on differences in ATP hydrolysis and synthesis
• 3 major types– Slow-oxidative (type I) fibers– Fast-oxidative (type IIa) fibers– Fast-glycolytic (type IIx) fibers