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70 Cards in this Set
- Front
- Back
what does skeletal muscle do?
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causes the bones to which muscle is attached to move.
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What does skeletal muscle allow?
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-respiration
-body movement -chewing/swallowing -heat generation - regulation of homeostatic systems. |
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how is skeletal muscle organised? describe...
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in a hierarchical system.
Muscle > muscle fiber > myofibrils > thick/thin filaments |
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what is a muscle cell?
another name? how long? |
a myofibril
sarcomere as long as the muscle. |
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what are each made of?
-thick -thin |
thick = myosin
thin = actin |
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what is the nucleation like in skeletal muscle?
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multinucleated, from fusing of many cells
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what is a
-Z line -M line |
Z = disc-shaped protein that holds thin filaments aligned.
M = disc-shaped protein that holds thick filaments aligned. |
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what are thick filaments made of?
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several hundred myosin proteins
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how is myosin arranged?
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tail = light meromysin
head = heavy meromysin |
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What two parts compose Heavy meromysin?
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S1 and S2 chains
S1 = light chains, head portion. S2 = the hinge. |
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What are the S1 regions of heavy meromysin?
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Crossbridges
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what is the light meromysin composed of?
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2 myosins coiled together in a tail.
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what are the two binding sites on the crossbridge of myosin?
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-ATP binding site
-Actin binding site |
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What binding site does Actin have?
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Myosin binding site.
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What other two molecules are with Actin?
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Troponin and Tropomyosin
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what is the role of
-troponin -tropomyosin |
Troponin: the coordinating molecule - binds everything!
Tropomyosin: covers the myosin bindng site in resting states. |
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what is the sliding-filament theory?
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just the statement that during sarcomere shortening, filaments move past ea. other, but don't shorten.
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which bands in the sarcomere get reduced during contraction?
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-I band narrows
-H band disappears |
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how is the ATP binding site on myosin an enzyme?
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-it hydrolyzes atp when bound
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what is the crossbridge cycle?
how many steps? |
the events that occur btwn cross-bridge binding to thin filament, its movement, and resetting to repeat.
-four steps |
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What are the four steps in the cross-bridge cycle?
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1. Attachment - crossbridge to thin filament.
2. Movement - thin fil tenses 3. Detachment 4. Re-energizing |
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What is the myosin crossbridge like in a resting muscle?
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-cocked and ready to go; ATP is split and ADP and Pi are still bound.
-Cytosplasmic Ca+ is low tho so no binding to actin. |
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What molecule initiates crossbrg cycling?
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CALCIUM!!! in the cytosol
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what is a Power Stroke?
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the movement caused when energized myosin crossbrg (with ADP and Pi) binds actin. immediately releases energy and causes movement.
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What breaks the link between myosin and actin? How?
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ATP binding decreases myosin's affinity for actin.
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What happens when ATP binds to myosin?
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Hydrolyzes and re-energizes myosin.
-If Ca still present, another cycle. |
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What are ATP's two roles?
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1. Hydrolysis provides energy for movement
2. Binding allosterically regulates myosin to decr. actin affinity. |
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What is rigor mortis?
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stiffening of dead body because ATP is not present to unbind myosin from actin.
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what is tropomyosin, and what does it do?
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rod like protein that binds 7 actin molecules, blocking their myosin binding sites.
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what is troponin, and what does it do?
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small globular protein that binds tropomyosin and actin; when Ca+ binds actin, it drags tropomyosin away and allows actin to bind myosin.
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What is excitation-contraction coupling?
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the link between action potential excitation in a muscle fiber's membrane, and how it causes a crossbridge cycle.
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In general, how does an action potential cause a crossbrg cycle?
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by increasing cytosolic calcium
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what is the cytosolic [Ca] in a resting muscle?
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very low = 10-7
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what is the source of cytoplasmic calcium when excited?
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sarcoplasmic reticulum
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what are lateral sacs?
what are they for? |
-enlarged regions of the SR sheaths around myofibrils;
-store calcium for release during excitation. |
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what are T-tubules?
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structures that are between SR sheaths around myofibrils; they circle at the A-I junction.
-continuous with plasma membrane; conducts Action potentials to the cell center. |
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what are the functions of the sarcoplasmic reticulum?
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-take up Ca
-store Ca -release CA |
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how does a T-tubule cause calcium release?
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action potential conducts through the T-tubule, to where it contacts Lateral sacs of SR, which release calcium into the cytosol.
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how is contraction stopped by the SR?
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Calcium ATPase pumps take calcium back up - takes a while though, so contraction lasts a long time.
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How can contraction strength of skeletal muscle be controlled?
(3 ways) |
1. By motor unit recruitment
2. By summation and tetany 3. By changing the initial muscle fiber length. |
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what kind of contraction is caused by ONE action potential?
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a twitch - very small contraction.
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how do you get more than a twitch?
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by motor unit recruitment:
-making more motor units fire. -making more muscle cells contract. |
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what prevents fatigue over time in muscle?
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asynchronous firing
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What is asynchronous firing?
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Variation in which muscle cells are firing during a contraction. 10 might be on, 10 off.
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What is summation?
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the concept that repetitive action potentials cause stronger and longer contractions.
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How are contraction strengths varied?
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By varying the number of AP within a given period of time; very fast/repetive firing causes summation so much that the cell doesn't even relax.
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What is tetani?
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fused contraction of muscle due to rapid firing of neuron - continuous action potentials - cytosolic Ca2+ is always high.
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How does changing initial muscle fiber length control muscle strength?
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If muscle is too short to begin with, less force will be generated. If too long, no crossbridges interact.
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what is the optimal crossbrdg overlap for muscle contraction?
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between 1.95 um and 2.25
-flat line because between these points, the H band will change no further. |
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what are two types of skeletal muscle contractions?
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-isometric
-isotonic |
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what is isometric contraction?
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That when muscle length stays the same.
-Load > force developed -Force increases but you're not moving anything yet. |
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what is isotonic contraction?
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that when muscle length changes because force > load.
-Force stays constant as the muscle contracts/relaxes. |
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what are 3 things that affect skeletal muscle energetics?
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-ATP source
-Oxygen debt -Type of skeletal muscle |
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what are 3 sources of ATP?
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-Creatine phosphate
-Oxidative phosphorylation -Glycolysis |
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How does Creatine phosphate generate ATP?
-What is ATP supplied for? -How fast? |
by phosphorylating ADP to produce Creatine and ATP.
-Supplies for FAST movement. -1 sec needed for reaction. |
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CP + ADP -> ?
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Creatine + ATP
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What generates ATP for endurance movement? Why?
(when O2 is present) |
-Oxidative phosphorylation - aerobic metabolism.
-B/c 36 ATPs are generated from every 1 glucose. |
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-What can be used for oxydative phosphorylation to generate ATP?
-What is required for Oxid phos? |
Fatty acids OR Glucose.
-Requires Oxygen and TIME -slow. |
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How much ATP is generated when no oxygen is present?
By what process? Is this for fast or endurance movement? |
-2 ATP + Pyruvate (breaks to lactic acid) from one glucose.
-Glycolysis - anaerobic metabolism. -fast - no enzymatic steps. |
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What is better for ATP generation, Creatine phsosphate or glycolysis? Why?
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Creatine phosphate - much higher yield, more efficient.
-Glycolysis generates 2 ATP but pyruvate has to be broken down to lactic acid. |
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what are 3 types of skeletal muscle based on their metabolic processes?
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SOX - slow oxididative
FOX - fast oxidative FGL - fast glycolytic |
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what is
-red meat -dark meat |
red = slow oxidative/fast oxid.
white = FGL - fast glycolytic. |
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where would fast oxidative muscle (type 2) be found?
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in your arms.
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which type of tissue resists fatigue the best?
whihc has least mitochondria? |
slow oxidative
fast glycolytic |
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what type of meat do sprinters have more of?
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white meat = fast glycolytic
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what type of meat do cross country runners have?
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slow oxidative
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If a sprinter trained to run long distance, what type of meat would develop?
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His type 3 fast glycolytic would become type 2 fast oxidative.
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on the force vs. length curve, what is the Optimal length?
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the length at which max isotonic force is developed - about 2 um.
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what effect does stretching a muscle beyond optimal length have on force developed?
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decreases it. b/c thick and thin filaments are overlapping and so fewer slide during the crossbridge cycle.
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what effect does contracting a muscle shorter than its optimal length have on force development? what two reasons?
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decreases it.
1. the z lines run into the thick filaments. 2. Thin filaments collide and no more contraction can occur - or they overlap and interfere with crossbg forming |