Term
| What are the essential functions of skeletal muscle? |
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Definition
Maintain body posture Stabilize joints Produce mvmt generate heat |
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Term
| What percentage of the body is skeletal muscle? How much is cardiac and smooth? |
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Definition
40% skeletal 10% cardiac and smooth |
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Term
| What is the main function of the sarcoplasmic recticulum? |
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Definition
It stores calcium ions Made up of the SR and terminal cisternae |
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Term
| What is the main function of the T tubules? |
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Definition
They bring action potentials into the interior of the muscle fiber T-tubule + terminal cisternae (on either side) = triad |
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Term
| Describe the structure of the thick filaments |
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Definition
One thick filament consists of >200 myosin molecules. Each Myosin molecule is made up of 6 polypeptide chains: 2 heavy chains and 4 light chains. 2 heavy chains (α-helical) coil around each other to form the tail 4 light chains (located on the 2 globular head regions): 2 are the actin-binding sites (alkali light chains) and 2 are the ATPase sites (regulatory chains) |
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Term
Describe the structure of the thin filaments |
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Definition
Contains actin, tropomyosin, and troponin G-actin monomers polymerize to make the 2x-stranded f-actin filamentous chain Tropomyosin blocks Myosin-binding site on actin molecule Troponin is a complex of 3 globular proteins: TnT attaches troponin complex to tropomyosin; TnC binds calcium; TnI prevents filament interaction and blocks myosin binding site on actin |
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Term
| Is there cross-bridge formation b/t actin and myosin in the H (bare) zone? |
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Definition
| No...this area contains only thick filaments- no thin |
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Term
| In a sarcomere during contraction, which zones/bands shorten in length and which remain unchanged? |
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Definition
I-band, H-zone shorten A band stays the same |
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Term
| What is the general function of other cytoskeletal proteins in myofibrils? List and describe their specific functions |
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Definition
They establish architecture of myofibrils and ensure correct alignment b/t thick and thin filaments Titin: extends from M line to Z disks; provides elasticity Nebulin: associates with thin filaments; keeps them aligned α-actinin: anchors actin filaments to Z disks Dystrophin: joins cytoskeleton to extracellular matrix |
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Term
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Definition
- Inherited fatal muscle wasting disese affecting mostly boys. Usually leads to death before 20.
sex-linked (Xchromosome) disorder or spontaneous mutation before or during conception = defective or absent dystrophin protein progressive muscle weakness starting at age 2-3; confinement to wheelchair by 10-12 clumsiness, waddling, frequent falls as toddlers skeletal deformity; curvature of spine (Kyphoscoliosis) mental retardation respiratory infections; heart failure No cure
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Term
| What are some of the experimental studies that have been made to discover treatment of muscular dystrophy? |
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Definition
intramuscular injection of dystrophin or gene for dystrophin immature muscle cells from father injected into muscles of son Inhibition of myostatin pathway (myostatin limits skeletal muscle growth) |
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Term
| Describe the molecular basis of muscle contraction |
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Definition
Beginning of cycle: myosin is tighly bound to actin in rigor state bindin of ATP to myosin head causes conformational change and myosin looses some affinity for actin further conformational change due to cleft tightening around ATP causes myosin to be displaced towards + end of actin. AtP is hydrolyzed by ATPase activity and ADP, Pi remain bound Myosin binds to new actin site (closer to + end) = power-stroke. Each cross-bridge walks myosin up 10nm Myosin head tilts and ADP, Pi is released and myosin returns to original state with no ATP bound
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Term
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Definition
| The greater the amount of work done by the muscle, the greater amount of ATP cleaved |
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Term
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Definition
It is the stiffening or contraction of muscle that occurs several hours (3-4) after death Results from ATP depletion peak rigidity occurs at 12 hours: inability of dying cells to remove calcium; calcium influx into muscle cells stimulates crossbridge formation; no ATP available for crossbridge detachment - actin and myosin are irreversibly cross-linked Muscle degeneration occurs after about 48 hours
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Term
True/False [Ca2+] in the SR controls strength and duration of contracton |
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Definition
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Term
| Do all sarcomeres contract at the same time? |
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Definition
| NO...they contract at different times. This allows continuous contraction of the muscle |
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Term
True/False In every type of muscle the mechanism by which tension is actively generated always involves sliding filaments |
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Definition
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Term
| Describe an isometric contraction |
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Definition
Muscle is allowed to develop tension, but not allowed to shorten; since muscle can't shorten to lift objects, it remains at constant length despite tension development. Can be active, passive, or total tension Cross-bridges form, but no sliding of filaments Tension does not exceed resistance
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Term
| Describe an isotonic contraction |
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Definition
| The muscle shortens while pulling a constant load (afterload);weight of object unchanged so muscle tension remains constant |
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Term
| Describe the length-tension relaitonship |
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Definition
Amount of tension a muscle generates depending on how stretched it is before it contracts Amount of tension is determined for isometric contractions 3 measurements of tension are made: Passive-is created by stretching muscle to different lengths Active- developed when muscle contracts (proportional to the # of crossbridges formed; is maximal at maximal overlap) Total- tension when muscle it stimulated to contract at different preloads |
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Term
| Describe the Force-Velocity relationship |
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Definition
Speed of shortening depends on afterload against which muscle must contract - which is determined by allowing muscle to shorten (isotonic contraction) Small load - faster velocity than large load No load = fastest velocity Maximal velocity depends on the fiber type |
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Term
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Definition
| A maximal sustained contraction acheived by continuous stimulation of a muscle fiber tot he point where it can't relax (action potential sum and lead to Treppe effect). Treppe (staircase effect) leads to tetanus |
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Term
| What is the major mechanism for adjusting strength of contraction in skeletal muscle? |
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Definition
Adjusting the frequency of action potentials traveling down a motor neuron to muscle fibers Other ways include recruitment of motor units and muscle fibers |
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Term
| What is an important mechanism for adjusting the strength of contraction in smooth and cardiac muscle? Why is this not important in skeletal muscle? |
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Definition
Adjust the sarcolemma permeability to calcium ions (open more channels) Not important in skeletal muscle because skeletal muscle fibers get calcium from the sarcoplasmic recticulum, not sarcolemma |
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Term
What is a motor unit? How does the number of motor units relate to muscle strength and tension? |
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Definition
Motor Unit: a single α-motorneuron and all the muscle fibers it innervates # of muscle fibers in a motor unit determines: strength of contraction and minimal increment of tension contributed by that unit Small motor units: fewer muscle fibers (2-3) = fine touch; slow conducting; readily excitable Large motor units: 1000s of fibers = powerful, coarse control |
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Term
| Tension generated by a muscle fiber depends on what factors? |
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Definition
Properties of individual muscle fibers: either slow oxidative (type I), fast oxidative-glycolytic (TypeIIa), fast-glycolytic (typeIIb) Properties of motor units Recruitment of motor units |
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Term
True/False Muscle fiber type is independent of the nerve that enervates the muscle fiber |
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Definition
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