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101_12AI_muscle - skeletal muscle why study this next 1...

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skeletal muscle - why study this next? 1) used for many body functions 2) controlled by the nervous system 3) we can now understand the electrophysiology of muscles a) voltage-gated channels in muscle b) transmitter-gated channels @ neuromuscular junction (= end-plate) c) propagation of Na spike across muscle surface to trigger contraction d) changes in intracellular [Ca 2+ ] i
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skeletal muscles are used to: walk grasp objects (especially food) chew swallow (initial steps) breathe move away from harm blink our eyes (to avoid dessication of the cornea) talk postpone passage of urine & feces (e.g., compare sphincter control in infant vs adult) generate heat (this will be covered in other lectures) what is common to these events? 1) ability to shorten when stimulated 2) ability to exert force in the direction of shortening what enables muscle to work for us? 3 properties 1) how muscles attach to bone 2) “sliding filaments” 3) spike mechanism in skeletal muscle this defines muscle considerations
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what should we study about skeletal muscle? 1) what happens when skeletal muscle contracts? flexor versus extensor 2) how does skeletal muscle contract? “sliding filaments” 3) what determines strength of contraction?
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images like this give impression that: 1) tendons, bones, and muscles are different tissues 2) bones are somehow attached to tendons 3) tendons are somehow attached to muscle bone tendon muscle “glue”? muscle could then move a bone… 1) if the muscle pulls on the tendon 2) & then the tendon pulls on the bone muscle tendon bone “glue”?
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therefore, when muscle contracts, it pulls on a collagen network that extends from itself into the tendon & then into the bone. a different view: bone, tendon, & muscle differ in various ways but they all contain the protein “ collagen 50% of total body protein by weight collagen hardened by Ca-phosphate collagen collagen filled with muscle cells instead, view this as collagen with 2 modified ends bone tendon muscle bundle tissue % collagen of total tissue weight composition so that muscle as much as 9 muscle cells surrounded by collagen network & sheath it can contract tendon 90 polymerized collagen it stretches very little bone as much as 35 “hydroxyapatite” (Ca-phosphate crystals) deposited on collagen fibers it’s less flexible & not compressible idea from previous slide
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what does contraction achieve? if skeletal muscle is attached to bone, then contraction has 2 goals: 1) agonist muscle moves bone 2) & stretches the antagonist muscle after muscles contract, they do not lengthen by themselves. they must be “stretched” by antagonist muscles note: no motoneuron releases inhibitory neurotransmitters. motoneurons never produce an IPSP in skeletal muscle.
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