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23 Cards in this Set
- Front
- Back
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what is the relationship between the number of neurons and the muscle cells they innervate.
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every muscle cell is innervated by only one neuron at one endplate. However, one neuron can innervate many muscle cells
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what are thin and thick filaments composed of?
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thick filament: myosin.
thin filament: actin, tropomyosin, troponin |
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what proteins on the surface of the t-tubules initiative the calcium release?
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voltage sensors on the membrane are in physical contact with calcium release channels of the SR. Depolarization of the sensors lead to opening of the Ca++ release channels in the SR.
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which types of muscle require Ca++ release for contraction?
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smooth muscle and cardiac muscle require Ca++ release. skeletal muscle does not.
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what proteins cause Ca++ release in cardiac and smooth muscle?
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voltage-gated Ca++ release channels.
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what pumps Ca++ into the SR?
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SERCA Ca++ pumps
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what are the 5 states of myosin during the contracting cycle?
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Cocked, cross-bridge, power-stroke, attached, and released states.
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what things are attached to myosin during each of its states?
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Cocked: ADP+P
Cross-bridge: ADP+P Power-stroke: ADP no P Attached: Nothing Released: ATP |
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what terminates the contraction?
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1. deactivation of Ca++ release channels when the t-tubule returns to resting potential.
2. Re-sequestration of intracellular Ca++ into the SR. |
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what two mechanism control the strength of skeletal muscle contraction?
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temporal and spatial summation
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what is the term for when action potentials are fired to the muscle cell before one muscle twitch can finish? what does that result in with high frequency action potentials?
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temporal summation. unfused or fused tetanus
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what is the factor that limits the strength of a contraction from one single action potential?
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Ca++ pump activity lowers the cytoplasmic concentration before the contraction can generate maximal force.
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what elements of the muscle ensure that force generation is slower than the duration of high cytoplasmic Ca++?
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series elastic elements: extensions of the tendon and elasticity of the thick and thin filaments mean that the initial force generation goes into stretching these fibers and not moving the limb.
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what is the state of the series elastic elements during fused tetanus?
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they are fully stretched, so all of the force generation goes into moving the limb
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what is spatial summation?
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recruiting more motor units
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what is the size principle?
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Small motor units are recruited first, then large ones get recruited if needed.
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why do slow-twitch fibers (Type I) have a slow rate of contraction?
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they have an isoform of myosin that does not hydrolyze ATP as fast.
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what causes slow-twitch fibers to be more red?
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large concentrations of myoglobin for more oxygen supply
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what are postural muscles rich in?
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slow-twitch (type I) fibers
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what are type IIa fibers?
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fatigue-resistant fast-twitch fibers
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what is the rate of contraction of type IIa fibers, and what is their fuel source?
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they have a myosin that hydrolyzes ATP faster. they have glycogen stores and glycolytic enzymes for fast ATP production, and also abundant mitochondria and myoglobin.
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what are type IIb fibers?
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fatigable fast-twitch fibers
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what is the rate of contraction of type IIb fibers?
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the fastest of any muscle fiber type.
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