Term
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Definition
| contractions that create force without moving a load |
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Term
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Definition
| a rigid bar that pivots around a point known as a fulcrum |
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Term
| What is missing in a victim of Duchenne muscular dystrophy? |
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Definition
| the structural protein dystrophin which links actin to proteins in the cell membrane |
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Term
| What is missing from the muscles in a victim of McArdle's disease (myophosphorylase deficiency)? |
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Definition
| the enzyme that converts glycogen into glucose 6-phosphate |
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Term
| 3 ways to categorize the different types of smooth muscle |
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Definition
1. location
2. contraction pattern
3. communication with neighboring cells |
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Term
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Definition
| muscles that undergo periodic contraction & relaxation cycles |
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Term
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Definition
| muscles that are continuously contracted; always maintain some level of muscle tone |
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Term
| 2 examples of tonically contracted muscles that close off the opening to a hollow organ |
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Definition
1. esophageal sphincter
2. urinary bladder sphincter |
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Term
| What is another name for single-unit smooth muscles? |
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Definition
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Term
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Definition
| the cells are not linked electrically & each muscle cell functions independently |
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Term
| Why is single-unit smooth muscle also called visceral smooth muscle? |
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Definition
| it forms the walls of internal organs such as the intestinal tract |
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Term
| Must smooth muscles be able to operate over a range of lengths? |
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Definition
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Term
| Within an organ, must the layers of smooth muscle run in the same direction? |
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Definition
| no! they may run in several directions |
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Term
| Do skeletal/cardiac muscles or smooth muscles contract & relax more slowly (when comparing a single muscle twitch)? |
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Definition
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Term
| Do skeletal muscles or smooth muscles use more energy to generate & maintain a given amount of force? |
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Definition
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Term
| Can smooth muscles sustain contractions for extended periods without fatiguing? |
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Definition
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Term
| Do smooth muscles or skeletal muscles contain large, multinucleated fibers? |
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Definition
| skeletal muscles (smooth muscles have small, spindle-shaped cells with a single nucleus) |
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Term
| In smooth muscle, are the contractile fibers arranged in sarcomeres? |
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Definition
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Term
| Can contraction in smooth muscle be initiated by electrical or chemical signals (or both)? |
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Definition
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Term
| Is smooth muscle controlled y the autonomic nervous system? |
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Definition
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Term
| Does smooth muscle have specialized receptor regions such as the motor end plates found in skeletal muscle synapses? |
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Definition
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Term
| Where does the Ca2+ for contraction come from in smooth muscle? |
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Definition
| ECF & sarcoplasmic reticulum |
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Term
| In smooth muscle, how does the cascade initiated by the Ca2+ signal end? |
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Definition
| phosphorylation of myosin light chains & activation of myosin ATPase |
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Term
| Smooth muscle cells have an extensive cytoskeleton consisting of intermediate filaments & _____ bodies in the cytoplasm & along the cell membrane |
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Definition
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Term
| 4 key points in smooth muscle contraction |
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Definition
1. an increase in cytosolic Ca2+ initiates contraction
2. Ca2+ binds to calmodulin (a calcium-binding protein found in the cytosol)
3. Ca2+ binding to calmodulin is the first step in a cascade that ends in phosphorylation of myosin light chains
4. phosphorylation of myosin light chains enhances myosin ATPase activity & results in contraction |
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Term
| 4 steps of relaxation in smooth muscle |
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Definition
1. free Ca2+ in cytosol decreases when Ca2+ is pumped out of the cell or back into the sarcoplasmic reticulum
2. Ca2+ unbinds from calmodulin
3. myosin phosphatase removes phosphate from myosin light chains which decreases myosin ATPase activity
4. less myosin ATPase activity results in decreased muscle tension |
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Term
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Definition
| a small regulatory protein chain that exists at the base of the myosin head |
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Term
| myosin light chain phosphatase (MLCP) |
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Definition
| an enzyme that dephosphorylates the myosin light chain & therefore decreases myosin ATPase activity |
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Term
| How can chemical signals such as neurotransmitters, hormones, & paracrine molecules alter smooth muscle Ca2+ sensitivity? |
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Definition
| by modulating myosin light chain phosphatase activity |
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Term
| pharmacomechanical coupling |
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Definition
| contractions initiated by chemical signals without a significant change in membrane potential |
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Term
| 2 things that mediate SR Ca2+ release |
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Definition
1. ryanodine receptor calcium release channel
2. IP3-receptor channel |
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Term
| calcium-induced calcium release (CICR) |
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Definition
| the process in which the RyR channel opens in response to Ca2+ entering the cell |
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Term
| What happens when SR Ca2+ stores decrease? |
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Definition
| a protein sensor on the SR membrane interacts with store-operated Ca2+ channels on the cell membrane |
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Term
| Voltage-gated Ca2+ channels open in response to _____ |
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Definition
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Term
| What is another name for ligand-gated Ca2+ channels? |
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Definition
| receptor-operated calcium channels (ROCC) |
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Term
| stretch-activated channels |
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Definition
| open when pressure or other force distorts the cell membrane |
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Term
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Definition
| when contraction (such as in stretch-activated channels) originates from a property of the muscle fiber itself |
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Term
| What kinds of cells are said to have slow wave potentials? |
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Definition
| cells that exhibit cyclic depolarization & repolarization of their membrane potential |
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Term
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Definition
| depolarizations that create regular rhythms of contraction |
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Term
| 2 ways that pathways that increase IP3 cause contraction |
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Definition
1. IP3 opens IP3 channels on the SR to release Ca2+
2. diacylglycerol (another product of the phospholipase C signal pathway) indirectly inhibits myosphosphatase activity |
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Term
| 3 ways that signals that increase cAMP production cause muscle relaxation |
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Definition
1. free cytosolic Ca2+ concentrations decrease when IP3 channels are inhibited & the SR Ca2+-ATPase is deactivated
2. K+ leaking out of the cell hyperpolarizes it & decreases the likelihood of voltage-activated Ca2+ entry
3. myosin phosphatase activity increases, which causes a decrease in muscle tension |
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