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img078 - individual fibers also plays a role but it is a...

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Unformatted text preview: individual fibers also plays a role but it is a secondary role after motor unit recruitment. Indeed, 3W PWs called recruitment Within a muscle, fibers belonging to a given motor unit are intermixed with fibers from other motor units. Not all motor units are equal - they oflen differ in size with some having more fibers than others. Those motor units with more muscle fibers are able to produce more force. When a muscle 1s called upon to generate small forces generally only the smaller motor units are called into action. When larger forces are required thear _lar__ger motor we activated ‘8 well with W Click the animation Button: This animation illustrates motor unit recruitment and force production. Note that when motor unit R is stimulated the muscle will shorten slightly. When both R and Y are recruited the muscle shortens more. Click the Return Button. mmmnmmw-mmmmm We. uni—s mmmmmw-WMW. Ammmmmmmmm. Click the Home Menu Button AMWmmu-nmmumumw M Oat-wan [E “mm-mmoh"” ....g mm m... m Click the Fiber Type Button: Although all skeletal mm“ Ii Monument-mumm- mourn-um muscle fibers are fimdamentally alike with respect to the W mun-.1. in. II? a...“ o, mm mm 1. 1., m. .f m mechanisms of excitafion—conu'acfion coupling and force mm W generation, there are difi'erences among them in terms of r: ”11"“ Mama—3.3) how quickly they can contract and how they produce most n...» of their ATP. When muscles are stimulated to contract isometrically some take longer to reach peak tension than others. The reason is that a muscle (such as gastrocnemius) contains different populations of fibers. Some muscles (e.g. Soleus) contain mostly slow twitch fibers that contract slowly. Other muscles contain largely fast twitch fibers that contract fairly quickly. Egsthtdtch "°"‘ '33 fibers “WWW- twitch fibers and also have hi 1gher maximum shortening fivelocities when they contract isotonically. 93‘ We describe skeletal muscle fibers based on 1) their contractile speeds, and 2) their metabolic capacities. Various combinations of contractile speed and metabolic capacities are possible. Based on the combination of contractile speed and metabolic capacity three major classes of skeletal muscle fibers have been identified — 1) slow .:- ' e fibers, 2) fast glycolytic fibers and 3) fast oxidative fibers. WM Go to the next screen: The difference between fast Sq. mm Yfim “mm contractile fibers (fast-twitch) and slow contractile . {>930 wmmm Dumas-«umw fibers (slow-twitch fibers) is based on the type of 0+» 5 -L. , rmmm‘ 1 1 mmmm myosin presentintheir thick filaments. Theyflmityof ,, «C3 , .— ‘ mWnQn depends on theymtegfimssbndge 46:3 to V . . If WW mm mm , a M) cyclin , which is limited by the gg—hmhngsnm — Q 05k own-d Inn-t mum-mumm- Wis. Fast myosin has the ability to J. . .1" 3 mm W hydrolyze ATP at a faster rate than slow myosin. o- <‘ m - §< ,( ’ wdm ATPase rate 13 highly correlated with a fiber's speed of a 2%33 Hints civilly dwely contraction. Fast fibers have a high AT Pase mpacity on a ”I Wm. M m the myosin head. 8 Page 7 of 8 ...
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