third test notes

third test notes - 1 Skeletal muscle 1 Each skeletal muscle...

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1. Skeletal muscle 1. Each skeletal muscle fiber is = to a muscle cell 1. Naturally multinucleate 2. Full of myofibrils (roughly 100/fiber) 1. These are full of actin and myosin filaments 3. Branch of motor neuron innervates each fiber 2. Skeletal muscle is striated because myofibrils are precisely aligned 3. Muscle fibers are large and multinucleate because they are formed by fusion of many muscle cells during development 1. Adaptation for generating power 2. Electrical nature of muscle 1. Each time a motor neuron fires, threshold is reached in skeletal muscle fiber and it contracts 2. Muscle fiber RP’s and thresholds are similar to axons 1. Surface has V-gated Na+ channels like an axon 2. AP sweeps over entire surface of muscle fiber 1. Is the signal for muscle to contract 3. filaments 1. Myosin head 2. Myosin tail 3. Polymerize and form a diomen (has two heads, but don’t contract together 4. Myosin filament is a polymer of myosin molecules 1. Contractile proteins that attach to and exert force on actin filaments 5. Myosin heads can be cocked with ATP 6. Cocked myosins can ratchet and cause contraction 7. Heads on opposite ends point in opposite directions 1. Actins are thinner filaments and are arranged close to myosins 8. Contraction occurs when cocked myosin heads bind to actins and ratchet 9. Each time a myosin head ratchets, it uses 1 ATP 10. The Z line is a structural protein that anchors actins 11. Sarcomere is a functional unit of skeletal muscle, defined as part from 1 z line to the next z line 1. Sarcomeres line up end to end from tendon to tendon 2. And are precisely aligned side to side which produces striations 3. Cross bridge cycle = cycle of binding ratcheting, and unbinding of myosin head ot actin 1. Insert diagram 2. At rest, myosin head is cocked but unbound 3. Myosin head binds to actin 4. Myosin heat ratchets 5. ATP breaks cross bridge and recocks myosin head 4. How AP’s and Calcium ++ initiate contraction 1. ACh released by motor neron opens depolarizing channels in musc. 1. AP spreads out n all directions from the synapse 2. AP causes V-gated Ca++ channels in muscle to open and Ca rushes in (like at synaptic knob)
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3. Running alon actin is the filament tropomyosin which has a troponin complex attached at regular intervals 4. At rest, myosin is cocked and wants to bind to actin but is blocked by tropomyosin 5. Ca++ binds to troponin causing structural change which moves the triopmyosin strand 1. Allowing myosin to bind to actin 2. Cross bridge cycles begin and continue as lon as (Ca++) is greater than 10 - 7 M (molarity) at less than 10 -7 M, realaxation occurs 6. AP’s cause Ca++ to be released via Ca++ channels from a muscle storage reservoir called the sarcoplasmic reticulum 5. T-tubule system 1. For max power, skeletal muscle must contract as synchronously as possible 1. For max power, need to get AP signal simultaneously to all myofibrils 2. AP races over surface of fiber then down t-tubules into interior 3. T’s in contact with and contain extracellular fluid
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third test notes - 1 Skeletal muscle 1 Each skeletal muscle...

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