Term
| What are the major contractile proteins, and what are the regulatory proteins? |
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Definition
Contractile: actin & myosin
Regulatory: troponin & tropomyosin |
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Term
| In resting muscle, describe the positioning of tropomyosin |
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Definition
| blocks the cross-bridge binding sites on actin so myosin heads cannot attach |
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Term
True or False
During contraction, the thin filaments become shorter |
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Definition
False
The length of the filament does NOT change, they are just pulled closer to the cener of the sarcomere |
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Term
| What happens to the I & A bands during muscle contraction? |
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Definition
I band (thin filaments) becomes shorter
A band is unchanged |
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Term
| Describe the mechanism of action in the sliding filament theory |
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Definition
-myosin heads form cross bridges with actin creating actomyosin
-X bridges grab & swivel along the actin chains of the thin filaments
-myosin heads move towards the center of the sarcomere, pulling actin with it |
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Term
| If 1 myosin's head stroke generates a 12mm movement, how is the total movement measured in cm? |
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Definition
| because thousands of sarcomeres are involved |
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Term
| What are the 3 major components of a thin filament? |
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Definition
| Actin in helical strands Tropomyosin covering actin's active sites Troponin molecule found every 7 G-Actin molecules |
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Term
| What are the 3 subunits of troponin? |
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Definition
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Term
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Definition
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Term
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Definition
| interacts with actin so myosin cannot interact with it |
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Term
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Definition
Binds to Ca2+ when it is available
-causes Trop-T to move, results in Trop-I and tropomyosin to change position
-myosin binding sites on actin are now exposed |
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Term
| What does tropomyosin do when it is not blocking actin's active site? |
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Definition
| changes its depth so that myosin heads can 'row' against actin |
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Term
| When will maximum contractile force be attained? |
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Definition
| When all available cross bridges on thick filaments align with thin filaments |
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Term
| What determines the amount of contractile force generated? |
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Definition
| the degree of muscle contraction |
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Term
| What generates a contraction force? |
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Definition
| the crossbridges forming between actin and myosin |
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Term
| What influences sarcomere length & the distance between striations? |
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Definition
| the degree of overlap between thick & thin filaments |
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Term
| Does a voluntary impulse originate from the brain or spinal cord? |
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Definition
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Term
| Does a reflex impulse originate from the brain or spinal cord? |
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Definition
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Term
True or False
An AP is not strong enough to initiate muscle contraction on its own |
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Definition
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Term
| What is the membrane potential of a resting muscle cell? |
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Definition
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Term
| From where is acetylcholine released, and what does it do? |
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Definition
myoneural junction
-depolarizes muscle fiber membrane
-mmb potential becomes positive
-generates an AP that will travel across whole muscle fiber |
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Term
| Why is it necessary to generate an action potential? |
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Definition
| this is the stimulus that will initiate muscle contraction |
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Term
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Definition
| Where 2 sarcoplasmic reticulums meet 1 T tubule |
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Term
| How does the AP travel across the entire muscle fiber? |
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Definition
| via transverse tubules, which works with sarcoplasmic reticulum to enable simultaneous depolarization of the muscle fiber |
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Term
| Why are T tubules unique in muscle fiber? |
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Definition
| they are only found in skeletal & cardiac muscle |
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Term
| How do T tubules communicate with the SR? |
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Definition
| via proteins in the triad junction |
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Term
| How is muscle contraction initiated? (detail!) |
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Definition
-Dihydropyridine receptor of T tubule releases Ca2+ into saracoplasm
-Ryanodine receptor detects Ca2+ and releases the Ca2+ from the SR as well
-causes 100X increase in [Ca2+] |
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Term
| What happens after muscle contraction is initiated? |
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Definition
| -Trop-C binds Ca2+, configural changes expose the myosin binding sites on actin |
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|
Term
True or False
Muscle contraction is the conversion of mecanical energy into chemical energy |
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Definition
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Term
| Why is ATP required in muscle contraction? |
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Definition
| to convert G-actin to F-actin |
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|
Term
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Definition
| tropomyosin displacement allows actin binding sites to react with ATP on myosin head, Ca2+ activates myosin ATPase |
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Term
| Summarize all steps of contraction |
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Definition
1. CNS sends impulse to resting muscle
2. AP arrives at motor end plate
3. Ach depolarizes sarcolemma
4. AP is transmitted by T tubules to SR
5. Ca2+ released from SR cisternae into sarcoplasm
6. Ca2+ binds to Trop-C
7. Tropomyosin exposes binding sites on actin
8. Actomyosin X bridge forms
9. Ca+2 activate myosin ATPase, ATP hydrolysed
10. X bridges form and break repeatedly to slide the filaments & shorten sarcomere |
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Term
| After ATP is converted to ADP + P, where do these products go? |
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Definition
| They are bound to myosin heads, releasing chemical energy to fuel muscle contraction |
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Term
| What two reactions are stimulated by the release of Ca? |
|
Definition
-Myosin ATPase activity
-exposure of actin's binding sites |
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Term
| What happens to the positioning of the myosin heads after the hydrolysis of ATP? |
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Definition
| they become perpendicular to the active sites on actin, then tilt and pull actin with them |
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Term
| After the myosin heads tilt, what happens? |
|
Definition
ADP + P are released, new sites exposed to bind another ATP
-myosin X bridges detach
-new AP depolarizes SR, cycle continues |
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Term
| What is required for the cycle of contraction to continue? |
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Definition
| adequate supplies of ATP & Ca2+ |
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Term
| What has to happen for contraction to stop? |
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Definition
| need to lower Ca2+ levels in the sarcoplasm to repolarize the sarcolemma & T tubules & regain RMP of -90mV |
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|
Term
| What compound stores Ca2+, and where? |
|
Definition
| calsequestrin, in the terminal cisternae of the sarcoplasmic reticulum |
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Term
| What happens when Ca2+ levels decrease? |
|
Definition
-X bridges between myosin & actin dissolve
-TropC/Ca2+ complex falls apart
-tropomyosin covers actin's binding sites |
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|
Term
| What is the role of acetylcholinesterase at the myoneural junction? |
|
Definition
| breaks Ach into acetate & choline |
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|
Term
| What do anticholinesterases do? |
|
Definition
| preven breakdown of Ach, so sarcolemma is continuously stimulated & contraction never stops |
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|
Term
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Definition
| prevents Ach from binding to sarcolemma's receptors, so muscle contraction cannot be stimulated |
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|
Term
| What does the Botulinum toxin do? |
|
Definition
| prevents Ach from being released, so no depolarization of sarcolemma occurs, no AP generated, no muscle contraction |
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|
Term
| Describe the steps of muscle relaxation |
|
Definition
1. Achase released, Ach broken down
2. Sarcolemma & T-Tubes repolarized
3. SR Ca2+ pump activated, Ca2+ returned to terminal cisternae
4. Actin-myosin X bridges terminated
5. Tropomyosin covers binding sites
6. Passive sliding of filaments
7. Sarcomere returns to resting length |
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|
Term
| What is the term for low blood calcium? |
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Definition
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Term
| When does milk fever typically occur? |
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Definition
| within 72 hours of calving |
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Term
| What causes hypocalcemia in milk fever? |
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Definition
-onset of milk production such that the cow can't absorb or mobilize enough Ca to meet the needs
-lots of Ca in colostrum, not much in blood |
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|
Term
| What is the 1st Stage of Milk Fever? |
|
Definition
-stiffening of muscles
-trembling
-stiff hind legs
-staggering |
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Term
| What is the 2nd Stage of Milk Fever? |
|
Definition
-cow cannot stand up
-cow is dull, cold to touch
-heavy breathing, fast heart beat
-poor muscle contractions |
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|
Term
| What is the 3rd Stage of Milk Fever? |
|
Definition
-lateral recumbency (flat on side, legs stretched out)
-almost unconscious
-bloat is common
-untreated = death |
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|
Term
| What is flaccid paralysis? |
|
Definition
| extreme weakness of muscles & loss of muscle tone |
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|
Term
| What receptor of the T tubule releases Ca2+ into the sarcoplasm? |
|
Definition
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|
Term
| What receptor of the SR releases Ca2+ into the sarcoplasm? |
|
Definition
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