Muscle Contractions Flashcards
Excitation
- AP in neuron sends signal to the axon terminal and opens voltage-gated calcium channels. Calcium ions enter axon terminal
- Calcium causes synaptic vessicle to release ACh into synaptic cleft
- ACh binds to ligand-gated receptors on sarcolemma/ motor end plate
- Receptors open - Sodium is in, potassium is out (end-plate potential)
- Voltage-gated receptors around motor end plate open up= AP #2 calcium can enter the cell
1 Action Potential =
- exocytosis of 60 vesicles
- each vessicle releases 10,000 molecules of ACh
____ causes the sarcolemma to be less negative while ____ causes it to be more negative
- Sodium
- Potassium
Stage: Excitation
Step: 1
Description: AP in neuron sends signal to the axon terminal and opens voltage-gated calcium channels. Calcium ions enter axon terminal
photo of step 2
Stage: Excitation
Step: 2
Description: Calcium causes synaptic vessicle to release ACh into synaptic cleft
photo of step 3
Stage: Excitation
Step: 3
Description: ACh binds to ligand-gated receptors on sarcolemma/ motor end plate
photo of step 4
Stage: Excitation
Step: 4
Description: Receptors open - Sodium is in, potassium is out (end-plate potential)
photo of step 5
Stage: Excitation
Step: 5
Description: Voltage-gated receptors around motor end plate take in sodium = AP #2
Excitation-Contraction Coupling
- APs are propogated from around motor end plate down the T Tubule
- Terminal cisternae of the SR releases calcium into the myofilaments
- Calcium binds troponin
- Tropomyosin shifts, exposing active myosin binding sites on actin
Stage: EC Coupling
Step: 1
Description: APs are propogated from around motor end plate down the T Tubule
Stage: EC Coupling
Step: 2
Description: Terminal cisternae of the SR releases calcium into the myofilaments
Stage: EC Coupling
Step: 3
Description: Calcium binds to troponin
Stage: EC Coupling
Step: 4
Description: Tropomyosin shifts, exposing active myosin binding sites on actin
Contraction
- Recovery stroke: Activation and cocking of myosin head while ATP hydrolysizes to ADP and Pi
- Formation of myosin-actin cross bridge
- Power stroke: Sliding of thin filament over thick filament
- Cross-bridge is broken when new ATP binds to myosin and steps are repeated as long as ATP is present
Stage: Contraction
Step: 1
Description: Recovery stroke - activation and cocking of myosin head while ATP hydrolysizes into ADP and Pi
Stage: Contraction
Step: 2
Description: Formation of MA cross bridge
Stage: Contraction
Step: 3
Description: Power stroke - ADP and Pi pop off of myosin head; sliding of thin filament over thick
Stage: Contraction
Step: 4
Description: Binding of new ATP; breaking of cross bridge
Relaxation
- No more nerve signal at NMJ = no more ACh
- ACH is broken down by AChE and is reabsorbed by the axon terminal
- Reabsorption of calcium ions by SR
- Calcium unbinds from troponin
- Tropomyosin returns to original position to block active actin binding sites
Stage: Relaxation
Step: 1
Description: No more nerve signal at NMJ = no more ACh
Stage: Relaxation
Step: 2
Description: ACh broken down by AChE and is reabsorbed by axon terminal
Stage: Relaxation
Step: 3
Description: Calcium is reabsorbed by SR
Stage: Relaxation
Step: 4
Description: Calcium unbinds from troponin
Stage: Relaxation
Step: 5
Description: Tropomyosin returns to original position and block active actin receptor sites
