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Define a muscle fiber
A muscle cell
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Define Sarcolemma
a muscle cell's cell membrane
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Define sarcoplasm
A muscle cell's cytoplasm
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Define fascicle
A bundle of muscle fibers
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Define myofibrils
Contractile/elastic protein bundles
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Define sarcoplasmic reticulum
A modified endoplasmic reticulum found in muscle cells
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Define a motor unit
A motor neuron and all the muscle fibers it innervates
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List the components of the muscle fiber
- Sarcolemma
- SR
- T-tubules
- Terminal cristernae
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What is the function on each component of the muscle fiber?
- Scarcolemma-plasma membrane
- SR-voltage modified ER
- T-tubules-lumen is in contact with ECF
- Terminal cristernae-direct Ca2+ release and allow AP form neuromuscular junction
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Describe the composition of Myosin
Two chains wrapped around each other with a myosin head(crossbridge) which contains an actin binding site, ATP binding site, and ATPase
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Describe the composition of Actin
Regulatory proteins troponin and tropomyosin
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What is the function of Titin?
huge and connect the thick filaments in elastic way
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What is the function of Nebulin?
Elastic giant molecule attaches to Z-disk and helps stabilize the thin filaments
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Describe the sliding filament theory of contraction
The thin filaments slide of the thick filaments causing the sarcomere to shorten
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What happens to the lengths of the various bands and zones during contraction?
- I-band: shortens
- Z-disk: shortens
- H-zone: shortens
- M-line: remains the same
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Describe the basis of contraction
- 1. Binding of myosin to actin
- 2. Power strokes
- 3. Rigor(low energy form)
- 4. Unbinding of myosin/actin
- 5. Cocking of myosin head (high energy form)
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Describe the regulation of contraction by tropomyosin and troponin
tropomyosin lies on the top of the active binding site-then AP depolarizes the T-tubules and the SR releases Ca2+-Ca2+ binds to troponin-tropomyosin is pulled off the active site-myosin crossbridge binds to actin
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Describe skeletal muscle relaxation
Cytosolic Ca2+ binds to SR Ca2+ channels--the channels close--Ca2+ is actively pumped back into SR by ATPase--cytosolic Ca2+ drops--Ca2+ unbinds from troponin--tropomyosin slides back over to cover the binding site--then the fiber relaxs
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List the sources of muscular ATP
creatine phospate + ADP-----creatine +ATP
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Explain how exercise intensity affects muscle metabolism
First it uses stored (very little) glycogen to make glucose. Then glucose and fatty acids are delivered through the blood stream. After approx. 30 min. the main energy sources is fatty acids.
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Describe how tension is generated in a single muscle fiber
???????
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Describe Summation
increased muscle tension
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Describe unfused tetanus
stimuli are apart so this allows the muscle to relax in between segments
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Describe fused tetanus
muscle reaches steady tension---this causes fatigue quickly
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Define isometric contraction
muscle develops tension but doesn't change length----- standing
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Define isotonic contraction
muscle shortens while the load remains constant-----picking up groceries
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Explain how fiber diameter affects force
The greater the diameter of a fiber the more actin and myosin it has. the more actin/myosin in a cell, the more crossbridges that can be formed so the more force that fiber exerts
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Describe fast twitch glycolytic fibers
Largest motor unit, least used, running/jumping
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Describe slow twitch oxidative fibers
smallest motor unit, most used, posture
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Describe fast twitch oxidative fibers
intermediate motor unit, standing/ walking
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List the possible causes of fatigue
- psychological effects
- protective effects
- lowered neurotransmitter effects (Ach)
- lowered receptor activation
- change in muscle membrane potential
- lowered Ca2+ release
- lowered Ca2+ troponin reaction
- depletion/accumulation theories
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Describe the composition of smooth muscle cells
- not striated--parallel
- coupled by gap junctions
- behaves as a single unit
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Describe smooth muscle contraction
Cell is depolarized--Ca2+ enters the cell from ECF--released from the SR--Ca2+ binds to protein calmodium--activates myosin kinase--phosphorylates light chains and myosin ATPase activity--activates myosin crossbridges--increase muscle tension
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Describe smooth muscle relaxation
Ca2+ is pumped out of the cell into SR--Ca2+ unbinds from calmodium--myosin phosphatase removes phosphate--decreases ATPase activity--decreases muscle tension
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