Skeletal Muscle Contraction
Terms
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- Define Contractility
- Capacity of MS fiber to undego shortening and change shape, becoming thicker
- Sarcomeres
- These sections shorten and become thick because the Actin filaments move toward the center this is constitues contraction
- Cross Bridges
- Myosin extensions that latch on to Actin and pulls them toward the center, shortening the Sarcomeres
- ATP
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-Energy needed to pull Actin strands together
-Require oxygen and glucose - Sliding Filament Theory
- Myson crossbridges attach to the Actin filament and bends, pulls on Actin it then releases and attaches to the next Actin binding site, pulling again. As long as ATP is avail and MS fiber is stimulated this will continue.
- Stimulus for MS Contraction
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-Acetylchlorine released from synaptic vesicle
-Motor end plate detects the neurotransmitter and MS IMPULSE spreads over the sacrolemma into the T tubules to the SR
-SR releases calcium to the sarcoplasm of the MS fiber
-calcium trigger and expose the Actin binding sites
-Sarcomere shorten (contraction occurs) - 2 Events of Relaxation
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1-enzyme breaks down the acetylcholine to prevent continuous stimulation of the MS fiber
2-Calcium returns to SR, LINKS ARE BROKEN between myosin and actin which causes relaxation - Threshold Stimulus
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Required stimuli for MS respond.
**Usually enought acetylcholine to reach a threashold stimuli is avail - "All or None"
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When MS gets threshold stimui it will respond to its fullest extent
**Increased stimuli will not affect a stronger MS response - Twitch
- A single contraction lasting a fraction of a second when some motor units are stimulated
- Fast Twitch Fibers
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-Power fibers
-Prone to Fatigue
-Develope bigger in diameter MS - Slow Twitch Fibers
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-Endurance fibers
-Fatigue resistant
-Develop more capallaries - TETANIC or TETANUS
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-Sustained contraction lacking even partial relaxation
-Spasm, like lockjaw - Recruitment
- All Motor units are activated and MS fibers are stimulated..."all or none"
- Sustained Contraction
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Recruitment (firing of MS)
Summation (series twitching)
acting together - Muscle Tone
- Appear at rest, but some sustained contraction is happening: posture
- Tonus
- Maintenance of tone due to the action of the nervous system keeping MS in a constant state of readiness
- Isotonic
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-Develop tension
-To cause or control joint movement
-dynamic contractions: varying degrees of tension change joint angles - Isometric
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Iso=same
Metric=length
-no change in MS length but there's increase in MS tension - 2 types of Isotonic contractions
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1) Concentric: shortening of MS
2) Eccentric: No shortening of MS, but lengthening with control, which creats tension - Passive
- Joint angle changes without MS contraction