UWL BIO 312 - Muscle mechanics, metabolism, and fiber type (2 pages)

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Muscle mechanics, metabolism, and fiber type



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Muscle mechanics, metabolism, and fiber type

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Lecture on the end of muscle mechanics, muscle metabolism, and the different types of muscle fibers


Lecture number:
21
Pages:
2
Type:
Lecture Note
School:
University of Wisconsin-La Crosse
Course:
Bio 312 - Human Anatomy and Physiology I
Edition:
1
Unformatted text preview:

Bio 312 Lecture 21 Lecture Outline I Muscle mechanics a Muscle twitch b Load velocity relationship c Load tension relationship II Muscle metabolism a Phosphagen system b Anaerobic pathway c Aerobic respiration III Fiber types Muscle Mechanics Muscle Twitch the mechanical contractile response to a single stimulus AP o Latent period between AP and development of external tension caused by Time needed to release enough Ca2 from sarcoplasmic reticulum Move tropomyosin cycle the cross bridges Series elastic component time it takes for elastic fibers to stretch and generate force o Twitch responses to different action potentials can summate o Tetanus tetanic summation AP s occurring at a fast enough rate to not let muscle relax at all o With increased stimulation frequency Ca2 in the sarcoplasm is persistently elevated allowing cross bridges to be active for a longer time o The series elastic componenet causes a dissociation between the tension generated directly by ross bridge activity within sarcomere internal tension and the external tension actually exerted on the afterload Elasticity of proteins and connective tissue in muscle fibers requires the muscle to be stretched before they can generate noticeable force on the afterload Length tension relationship tension force a muscle can produce from different resting lengths o Preload how stretched out a muscle is just prior to contraction o Optimum length is 100 of resting length allows for perfect overlap of cross bridges and thin filaments Under or overstretching does not allow for maximum amount of cross bridge thin filament connections Muscles will generally stay within 70 130 of their resting length o Titin elastic structural protein that keeps thick filaments aligned Prevents overstretching of sarcomere allows for elastic recoil after passive stretch Load velocity relationship as load on a muscle increases the speed at which that muscle can contract decreases with increase in load Will decrease until velocity reaches 0 and cannot lift weight Tension developed by each fiber o Action potential frequency frequency tension relation twitch wave tetanic frequency o Fiber length length tension relationship o Fiber diameter thicker fibers contain more functional sarcomeres o Fatigue Number of active fibers o Number of fibers per motor unit o Number of active motor units Muscle metabolism Hydrolysis of ATP by myosin energizes the cross bridges providing he energy for force generation binding of ATP to myosin dissociates cross bridges bound to actin allowing the bridges to repeat their cycle of activity Hydrolysis of ATP by the Ca2 ATPase in the sarcoplasmic reticulum provides the energy for the active transport of calcium ions into the reticulum lowering calcium to prerelease levels ending the contraction Hydrolysis of ATP to power Na K pump in sarcolemma ATP is the immediate source of energy for muscle contraction but is not stored in high concentrations so must be synthesized at a high rate Phosphagen system direct phosphorylation 1 1 ratio of CP and ADP o Coupled reaction of the breakdown of creatine phosphate for the synthesis of ADP ATP o No oxygen use can provide energy for around 15 seconds of intense physical activity o Essential for short duration high intensity activity o Creatine supplementation allows for more intense workouts because of increase creatine phosphate levels in the muscles allowing for increased lengths of intense workout Anaerobic pathway glycolysis and lactic acid formation o Breakdown of glucose from glycogen breakdown or delivered from blood to form 2 ATP and lactic acid which is a main cause of muscle fatigue o Does not rely on oxygen produces ATP at relatively high rate but is inefficient o Can provide energy for significantly longer than phosphagen system Aerobic pathway cellular respiration o Use of glucose fatty acids and or amino acids and oxygen to produce 32 ATP o Fatty acid is preferred fuel for respiration o Requires oxygen but can provide energy for very extended periods of time Phosphagen system can produce ATP at highest rate but for the shortest duration Anaerobic pathway can produce ATP at a high rate for relatively low duration and produces lactic acid Aerobic pathway is the slowest but can utilize many fuels and can produce ATP for long period of time As duration of activity increases reliance on aerobic pathway increases Fiber Types Skeletal muscle is not a homogenous tissue not all muscle fibers are identical Most muscles composed of muscle fibers with different mechanical and metabolic properties Fiber types are classified on the basis of morphological mechanical and metabolic properties o Twitch time related to rate of Myosin ATPase activity and Ca2 kinetics speed it is pumped out o Amount of tension developed related to fiber diameter o Resistance to fatigue some fibers respond better to repetitive stimulation while others get tired more quickly Fatigue inability to maintain tension with prolonged stimulation o Major system for producing ATP o All different types have different strengths and weaknesses in each category Slow Oxidative Fibers Type I fibers o Slow twitch lots of mitochondria small diameter small motor unit size relies on oxidative phosphorylation o Slow rate of fatigue slow calcium kinetics high capillary density o High myoglobin content used for binding oxygen for cellular respiration Gives meat red color Fast Glycolytic Fibers Type IIx fibers o Fast twitch few mitochondria large diameter large motor unit size relies on glycolysis phosphagen system o High rate of myosin ATPase and calcium kinetics o Low myoglobin content gives meat a white color


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