Sliding Filament Mechanism
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Transcript of Sliding Filament Mechanism
Sliding Filament Mechanism
Ch. 10-3 notes
Sliding Filament Mechanism
• Describes the cause and mechanism of muscle contraction
• Myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere
• The thin filaments are pulled toward the M line and meet at the center of the sarcomere
• The Z discs come closer together and the sarcomere shortens.
• This shortening shortens the entire muscle
Sliding Filament Mechanism
The Contraction Cycle
• Contraction– SR releases Ca2+ ions into the cytoplasm– Ca2+ binds to troponin to move tropomyosin out
of the way of the myosin-binding sites on actin– Contraction cycle – repeating sequence of events
that causes the filaments to slide• 4 steps
4 Steps to Contraction Cycle
1. ATP hydrolysis– Breaking ATP into ADP + P adds energy to the
myosin head so it can turn2. Attachment of myosin to actin to form cross-
bridges– Myosin head attaches to binding site on actin– Releases P– Crossbridge forms
4 Steps to Contraction Cycle
3. Power Stroke– Myosin crossbridges rotate
4. Detachment of myosin from actin– Myosin remains attached until another ATP binds causes
it to detach– * rigor mortis
Contraction cycle continues- with ATP- with Ca2+ levels high enough
Contraction Cycle
Contraction
• The myosin heads “walk” down the actin• They can attach and detach about 5 times per second
http://www.dnatube.com/video/4154/Muscle-Contractionhttp://www.dnatube.com/video/1305/Muscle-Contractionhttp://www.dnatube.com/video/1306/Muscle-contractionhttp://www.dnatube.com/video/1308/Muscle-Contraction
http://www.sci.sdsu.edu/movies/actin_myosin_gif.html
Neuromuscular Junction (NMJ)
• Somatic motor neurons – neurons that stimulate skeletal muscle fibers
• Place where action potentials arise• Synapse – region where 2 neurons or 1 neuron
and a target cell (muscle fiber) meet• Synaptic cleft – gap that separates two cells• Neurotransmitter – chemical released for the
2 cells to communicate
NMJ
NMJ
NMJ
NMJ Parts
• At the end of each axon are synaptic vesicles filled with acetylcholine (ACh)– ACh is the neurotransmitter
• Motor end plate – sarcolemma opposite the synapse– Contains acetylcholine receptors
• Action potential starts here with stimulation from neurons
Action Potential
1. Release of ACh– Vesicles do exocytosis– Diffuse to motor end plate
2. Activation of ACh receptors– 2 Ach bind to motor end plate and opens the
receptor– Na+ flows across membrane through channel
Action Potential
3. Production of muscle action potential– Na+ makes fiber more + charged– This causes release of Ca+– Contraction cycle!
4. Termination of ACh activity– Acetylcholinesterase (AChE) – breaks down ACh
so further muscle contractions don’t occur– Unless more ACh is released
Overview