muscle fiber
DESCRIPTION
Muscle fiber. Motor neuron. Nucleus. Sarcoplasmic reticulum (SR). Sarcolemma. Myofibrils. SR Cistern. T-tubule. Action potential reaches synaptic terminal of motor neuron. New AP generated at motor end-plate and propogated down T-tubules. Myofibrils (relaxed). Sarcomere. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Muscle fiber](https://reader036.vdocuments.us/reader036/viewer/2022062501/568167d3550346895ddd2664/html5/thumbnails/1.jpg)
Muscle fiber Motor neuron
Nucleus
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Sarcolemma MyofibrilsSarcoplasmic reticulum (SR)
T-tubule
SR Cistern
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Action potential reaches synaptic terminal of motor neuron
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New AP generated at motor end-plate and propogated down T-tubules
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Myofibrils (relaxed) Sarcomere
(Sarcolemma and other structures not shown)
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Myofibrils (contracted) Sarcomere
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Sarcomere (relaxed)
Actin(thin filaments)
Myosin(thick filaments)
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Sarcomere (contracted)
Actin(thin filaments)
Myosin(thick filaments)
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Actin(thin filament)
Myosin(thick filaments)
Myosinheads
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Actin Myosin head
ADP and phosphate
Protein complex
Note that ATP is hydrolyzed at this point, but still attached to myosin head.
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Calcium ion
Myosin-binding sites (exposed)
Protein complex
ADP and phosphate
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Actin Myosin head
ADP and phosphate
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Actin Myosin head
Pi
ADP
1. Release of Pi initiates the power stroke. 2. At the end of the power stroke, ADP is released. 3. A new ATP is required for myosin to release its hold on actin.
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Actin Myosin head
ATP
ATP binds to the myosin head, causing it to detach from actin.
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Actin Myosin head
ADP and phosphate
When the ATP is broken down to ADP and phosphate, the myosin head extends.
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Actin Myosin heads
The sequence repeats as long as calcium ions are present. The combined work of many myosin heads causes the actin filaments to slide past the myosin filaments.
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Actin Myosin headsProtein complex
When the action potentials stop, calcium ions are pumped back into the ER, the myosin-binding sites on actin are again blocked, and the muscle relaxes.
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ActinMyosinCalcium
Sarcomere
(Ca+2 in green)