Term
| Contraction-Relaxation Cycle |
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Definition
1. Tight binding the rigor state. The cross-bridge is at a 45° angle relative to the filaments.
2. ATP binds to its binding site on the myosin. Myosin then dissociates from actin.
3. The ATPase activity of myosin hydrolyzes the ATP. ADP and Pi remain bound to myosin.
4. The myosin head swings over and binds weakly to a new actin molecule. The crossbridge is now at 90° relative to the filaments.
5. Release of Pi initiates the power stroke. The myosin head rotates on its hinge, pushing the actin filament past it.
6. At the end of the power stroke, the myosin head releases ADP and resumes the tightly bound rigor state. |
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Term
| Events at neuromuscular junction → |
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Definition
| excitation-contraction coupling → Ca2+ signal → contraction-relaxation cycle → muscle twitch or sliding filament theory |
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Term
| Excitation-Contraction Coupling |
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Definition
1. Somatic motor neuron releases ACh at neuromuscular junction.
2. Net entry of Na+ through ACh receptor-channel initiates a muscle AP.
a. Voltage-gated channels connected to SR causes Ca2+ to be released.
3. ATP in t-tubules alters conformation of DHP receptor.
4. DHP receptor opens Ca2+ release channels in SR and Ca2+ enters cytoplasm.
5. Ca2+binds to troponin, allowing strong actin-myosin binding
6. Myosin heads execute power stroke.
7. Actin filament slides towards center of sarcomere. |
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Term
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Definition
1. Larger area of dispersal for NT
2. Always excitatory, no inhibitory (depolarization)
3. Na+/K+ channel opens
4. 1 neural “synapse” (string of varicosities) per muscle cell
5. Delay caused by time it takes for Ca2+ to cause release of NT for next AP |
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Term
| Length-Tension Relationship |
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Definition
1. Two extremes
a. No overlap because myosin heads are not attached to actin.
b. Maximum overlap achieved; no additional overlap can occur.
2. Number of myosin heads attached to actin influences amount of force that can be generated |
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Term
| Muscle Fatigue (Two Types) |
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Definition
1. Central Fatigue
a. Occurs in the CNS, may be caused by psychological effects or protective reflexes
Peripheral Fatigue
a. At the neuromuscular junction: caused by decrease in NT release or decrease in receptor activation
b. During excitation-contraction coupling: caused by change in muscle membrane potential
c. Ca2+ signal: caused by decrease in Ca2+ release or decrease in Ca2+ troponin interaction
d. During contraction-relaxation coupling: depletion theories: PCr, ATP, |
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