Skeletal Muscle Contraction Flashcards
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?
- Z lines move closer together
- Length of A band is constant
- 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 ?
- Motor AP travels along motor neuron to motor endplate at neuromusc junction
- ACh released – acts on sarcolemma
- Trigger AP in muscle
- Propagates down T-tubule membranes into interior of muscle fibers
- causes release of ca2+ sequestered in SR (inside the cell)
- Leads to shortening of sarcomere
How is a muscle lengthened?
By innervation and contraction of an antagonist muscle
What does each bind to:
- Troponin C
- Tropoinin I
- Troponin T
- c binds calcium
- I binds actin - inhibits actomyosin ATPase
- 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)
- ATP binds to myosin head -dissociation
- ATP is hydrolyzed-myosin heads to return to resting conformation
- A crossbridge forms and myosin head binds to new position on actin
- P is released. Myosin heads change conformation
- ADP is released
How much energy is stored in ATP as it is transformed into mechanical work in the crossbridge cycle?
30%!!
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
- latent period
- contraction phase
- 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:
- other name
- Fatigue
- Color
- Type I
- resistant
- red - myoglobin
Describe a fast twitch iia fiber:
- Fatigue
- color
- Resistant
2. Red-myoglobin
Describe a fast twitch IIB fiber:
- fatigue
- color
- fatigable
2. white - low myoglobin
Describe a slow twitch fiber:
- metabolism
- mitochondria content
- glycogen level
- oxidative
- high
- low
Describe a fast twitch IIA fiber:
- metabolism
- mitochondria content
- glycogen level
- Oxidative
- Highest
- abundant
Describe a fast twitch IIb fiber:
- metabolism
- mitochondria content
- glycogen level
- Glycolytic
- few
- high
