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8 Cards in this Set
- Front
- Back
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Define tension, load, isometric contraction and isotonic contraction. |
--Tension: force exerted by muscle on object --Load: force exerted by object on muscle --Isometric contraction: load is equal to or greater than tension, no shortening, constant length of muscle. Tension is measured during isometric contractions. --Isotonic contraction: tension is greater than load, muscle shortens, constant tension. Length is measured during isotonic contractions. |
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Describe how changing the load on a muscle fiber affects the velocity of contraction. |
As load increases, the distance of shortening decreases, duration of contraction decreases and velocity of contraction decreases. |
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Describe how changing the frequency of stimulation affects muscle tension. |
Summation: increased tension due to an increase in frequency of action potentials. --Unfused tetanus: oscillating summation tension --Fused tetanus: sustained summated tension |
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Describe how changing the initial length of a muscle fiber affects the cross bridge alignment and how this affects muscle tension. |
Optimal length: initial length that produces maximal active tension. This occurs at the maximal overlap of thick and thin filaments. Range of muscle length: muscle normally operate +/- 30% of the maximal muscle length. 70% (short)=40% tension 80% (short)=80% tension 90-110%=100% tension 120% (long)=90% tension 170% (long)=5% tension
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Describe how recruitment of motor units affects tension in the whole muscle. |
Recruitment: activation of multiple motor units. This is the primary mechanism by which tension of an entire muscle is regulated. [increases tension] |
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Compare the microanatomy of smooth muscle with skeletal muscle. |
-Smaller than skeletal muscle fibers -no myofibrillar structure (filaments arranged diagonally) -no transverse tubules -no troponin -dense bodies: anchor thin filaments -dense bands: attach filaments to membrane -intermediate fiber: link dense bands to dense bodies -intermediate junction: attachments between cells -gap junctions: allows electrical communication between smooth muscle cells -innervation from ANS |
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List the steps of excitation-contraction coupling in smooth muscle and how it differs from skeletal muscle. |
1. Ca2+ binds to calmodulin 2. Ca2+ calmodulin complex binds to myosin light-chain kinase 3. Myosin light-chain kinase phosphorylates myosin with ATP 4. Phosphorylated myosin binds to actin and begins the cross bridge cycle 5. cross bridge cycling is terminated and smooth muscle relaxes when the myosin is dephosphorylated by myosin light-chain phosphatase |
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List the sources of Ca2+ used for contraction in smooth muscle. |
--External (extracellular) calcium is the major source of calcium used in contractions --Sarcoplasmic reticulum: stimulated by influx of extracellular Ca2+; second messenger induced release (IP3). |
