Skeletal Muscle Contraction Flashcards Preview

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Flashcards in Skeletal Muscle Contraction Deck (29)
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What is the Z line?

The boundary between two sarcomeres


What is the I band?

Composed of only actin filaments
-extends from Z towards center of sarcomere
-appears light


What is the A band?

Composed of myosin thick filaments
-appears dark


What is the H zone?

location of NO overlap between actin and myosin


What is the M-line?

The center of the sarcomere
-site where thick filaments are linked with eachother


What occurs to the Z lines, A bands, I bands during muscle contraction?

1. Z lines move closer together
2. Length of A band is constant
3. Length of I band shortens


What is a myosin molecule made up of?

-2 heavy chains
-4 light chains
2 regulatory chains
2 essential or alkali chains


What is a myosin filament made up of ?

200 or more individual myosin molecules
-equal to the length of the A band


What are the 6 steps involved in excitation coupling (innervation) of a skeletal muscle ?

1. Motor AP travels along motor neuron to motor endplate at neuromusc junction
2. ACh released – acts on sarcolemma
3. Trigger AP in muscle
4. Propagates down T-tubule membranes into interior of muscle fibers
5. causes release of ca2+ sequestered in SR (inside the cell)
6. Leads to shortening of sarcomere


How is a muscle lengthened?

By innervation and contraction of an antagonist muscle


What does each bind to:
1.Troponin C
2. Tropoinin I
3. Troponin T

1. c binds calcium
2. I binds actin - inhibits actomyosin ATPase
3. T binds to tropomyosin


What is the cycle of contraction in a sarcomere, starting when the myosin head is in an attached state? (5 steps)

1. ATP binds to myosin head -dissociation
2. ATP is hydrolyzed-myosin heads to return to resting conformation
3. A crossbridge forms and myosin head binds to new position on actin
4. P is released. Myosin heads change conformation
5. ADP is released


How much energy is stored in ATP as it is transformed into mechanical work in the crossbridge cycle?



What is the contraction generated by a single action potential called?

A twitch


What is genetically distinct between the slow twitch, and two fast twitch fibers?

They differ in the myosin heavy chain they encode for
-different rates of ATP hydrolysis
-influence speed of crossbridge cycle and muscle contraction


Describe the phases of a graph for an isometric contraction - tension vs time

1. latent period
2. contraction phase
3. relaxation phase


What is the active tension ?

The difference between total tension and passive tension


When is tension of the muscle the greatest?

When there is maximal overlap between thick and thin filaments - number of crossbridges is the greatest


At which two states does zero tension exist in a muscle?

-When the muscle is stretched beyond the optimal length and there is no thin and thick overlap

-When the thick filaments contact the Z lines


What are satellite cells?

-Quiescent undifferentiated cells which mediate repair and growth


How do satellite cells assist in growth of skeletal muscle?

-They fuse into existing multinucleate myofibers and increase myofibril protein production


What is the result of a loss of myostatin in the mice experiment?

-uncontrolled hypertrophy
-altered satellite activation


What is the drug MYO-029?

-recombinant human AB that binds to inhibit myostatin activity
-used to treat muscular dystrophy


Describe a slow twitch fiber:
1. other name
2. Fatigue
3. Color

1. Type I
2. resistant
3. red - myoglobin


Describe a fast twitch iia fiber:
1. Fatigue
2. color

1. Resistant
2. Red-myoglobin


Describe a fast twitch IIB fiber:
1. fatigue
2. color

1. fatigable
2. white - low myoglobin


Describe a slow twitch fiber:
1. metabolism
2. mitochondria content
3. glycogen level

1. oxidative
2. high
3. low


Describe a fast twitch IIA fiber:
1. metabolism
2. mitochondria content
3. glycogen level

1. Oxidative
2. Highest
3. abundant


Describe a fast twitch IIb fiber:
1. metabolism
2. mitochondria content
3. glycogen level

1. Glycolytic
2. few
3. high