Unit V: Movement Muscle Contraction - Part I Chapter 9 – pg 286-291.
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Transcript of Unit V: Movement Muscle Contraction - Part I Chapter 9 – pg 286-291.
Electrophysiology of Muscle TissueReview
• Resting, excitable cell – polarized
• Resting muscle cell: excess Na+ outside, K+ and anions inside
• Resting Membrane Potential
• Stimulation of muscle cell – Na+ enters, then K+ leaves
• Action Potential
• spreads along the sarcolemmaMotor neuron
Axon
Motor end plate
Neuromuscularjunction
Myofibril
Muscle fiber
Excitation of a Muscle FiberSteps 1 & 2
1. Nerve signal opens voltage-gated calcium channels. 2. Calcium stimulates exocytosis of synaptic vesicles containing ACh = ACh release into synaptic cleft.
3. Binding of ACh to receptor proteins
4. opens Na+ and K+ channels resulting in reversed polarity forming an end-plate potential (EPP).
Excitation of a Muscle FiberSteps 3 & 4
Excitation of a Muscle FiberSteps 5
5. Voltage change in end-plate region (EPP) opens nearby voltage-gated ion channels producing an action potential
Excitation-Contraction CouplingSteps 6 & 7
6. Action potential spreading over sarcolemma enters T tubules 7. voltage-gated channels open in T tubules causing calcium gates to open in SR
Excitation-Contraction CouplingSteps 8 & 9
8. Calcium released by SR binds to troponin.
9. Troponin-tropomyosin complex changes shape and exposes active sites on actin.
Resting Sarcomere
Myosin head
Troponin
ActinTropomyosin
ContractionSteps 10 & 11
10. Myosin ATPase in myosin head hydrolyzes an ATP molecule, activating the head and “cocking” it in an extended position.
11. It binds to actin active site forming a cross-bridge.
ContractionSteps 12 & 13
12. Power stroke = myosin head releasesADP and phosphate as it flexes pulling the thin filament past the thick
13. Recovery stroke =with the binding of more ATP, the myosin head extends to attach to a new active site
Contracted Sarcomere
ContractionSliding Filament Theory
http://www.youtube.com/watch?v=WRxsOMenNQM
• Thick and thin filaments slide past one another• They DO NOT become shorter!• Half of myosin heads bound to thin filaments at a time
Sarcomere at restZ line Z lineH band
I band A band I band A band
Z line Z lineH band
Sarcomere contraction and filament sliding
RelaxationSteps 14 & 15
14. Nerve stimulation ceases 15. Acetylcholinesterase removes ACh from receptors. Stimulation of the muscle cell ceases.
RelaxationSteps 16
16. Active transport needed to pump calcium back into SR to bind to calsequestrin.
RelaxationSteps 17 & 18
17. Loss of calcium from troponin. 18. Moves troponin-tropomyosin complex over active sites. Muscle fiber returns to its resting length.
Rigor Mortis
• Hardening of muscles, stiffening of body
• Time period: 3 – 60 hours after death
• No ATP being produced!