Lecture 16 – Muscle Physiology IV

Affects tension development number of thin and thick

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Affects tension development – number of thin and thick fibers per cross sectional area is  about the same in all types of skeletal muscle fubers The greater diameter of a muscle fiber, the reater the number of think and thin  fimalemtns acting in parallel to produe the foce and the freater the maximum tension The maximum tension tou can produce is how many are acting in parallel One chain of sarcomere that is long and one that is short will not have a change in  tension If you want to get more tension, you nedd to add parallel fibers  Glycolytic fubers can produce greater maximal tension per muscle cell  Because they have a bigger diameter Rates at which they fatigue Fast glycolytic fibers fatigue rapidly  Slow oxidative fiber are very slow to fatigue cain maintain contractile activity for  extended periods of time  Fast oxidative are intermediate Whole Muscle Contraction Motor unit is one somatic motor neuron and all of the muscle fibers it innervates A musle fiber is innervated by only a single SMN All of the msucel fibers in a motor unit are of the same time  Therefore motor units ca be delineated by the kind of muscle that the SMN innervates How do you get a graded response?
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Activating different numbers of motor units Fine muscles have SMNs attached to a few fibers, whereas large muscles do larger  gradations with thousands of fibers Control of Tension The total tension a muscle develops depends on  Tension developed by each fibers Number of fibers contracting at a given time This depends on how many fibers are in a motor unit Also on how many motor units are activated Motor unit composition can vary The force that a given fiber produces depends partially on its diameter Glycolytic fibers have greatest diameter Thus a FGF produces more force than SOF Also, motor units of FGF tend to have more fibers per unit More force AND more fibers Nerve Stimulation Needed to contract motor unit Rate of stimulation adjusts the force produced by active cells Summation If you only fire for a little, you get a twitch from every fiber, not sustained contraction Contribution to total tension is dependent on the rate at which the SMN is firing Force production depends on number of myosin molecules per CSA 
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Contraction of intact muscles depends on the types and number of motor units In skeletal muscles each motor unit contracts in an all or none manner, graded  contractions are produced by Varying the types of motor units that are active Varying the number of motor units that are active Force of contraction can increase by increasing the number of motor units recruited 
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