M2 L3 Flashcards
What are the cross bridge cycle steps?
Discuss step 1 of the cross bridge cycle:
* discuss Ca2+ and ADP
- Calcium binds to troponin, moving tropomyosin and exposing actin’s binding sites.
At first, it is relaxed and not touching. This means low intracellular Ca2+. ADP and Pi are bound to the head of the myosin
Discuss step 2 of the cross bridge cycle:
* discuss Ca2+ and ADP
- the cocked myosin head attaches to actin, forming the cross-bridge. This is bc the troponin-tropomyosin complex experiences a conformational change due to inc Ca@+ which moves and reveals the myosin binding site.
- Ca2+ is elevated intracellular (released from SR from muscle cell stimulation)
- Pi is first released from head of myosin once contact is made
Discuss step 3 of the cross bridge cycle:
* discuss Ca2+ and ADP
- Power stroke – Once the myosin head is bound to actin, this triggers the stored energy in the cocked head to be released in the form of a conformational change.
This release of energy causes the myosin head to pivot, which results in the power stroke—pulling the thin filament inward toward the center of the sarcomere, causing the muscle to contract.
- ADP is released during the power stroke
- Ca2+ is high
Discuss step 4 of the cross bridge cycle:
- After the power stroke, ATP binds to the myosin head again, causing the myosin head to detach from actin but stay in the same position.
Discuss step 5 of the cross bridge cycle:
* discuss ATP hydrolysis
- The ATP that just binded to the myosin head is hydrolyzed (broken down) into ADP and Pi, which re-energizes the myosin head.
The myosin head is now back in the cocked position, ready to form another cross-bridge with actin and repeat the process.
- ATP Hydrolysis:
The enzyme myosin ATPase on the myosin head breaks down ATP into ADP and Pi (inorganic phosphate).
This reaction provides energy that is used to re-cock the myosin head. The energy released during this process is stored in the myosin head and used during power stroke.
What two things are necessary for the cycle to be able to repeat itself?
- elevated calcium
- ATP present
In a cadaver, the cross bridge position is in rigor mortis. explain why
The Ca2+ is high and so we can get to the step where ADP is released, but since there is no ATP, we will get stuck at step 3 after the power stroke happens. It gets stuck there and stiffens up. ATP is crucial for detaching the myosin head from actin and resetting the muscle contraction cycle.
For sarcomeres in parallel, how do they affect force production?
Adding sarcomeres in parallel increases the force production of a muscle. This arrangement doesn’t change the length of the muscle, but it increases the total cross-sectional area of the muscle.
The force generated by a muscle fiber depends on the number of cross-bridges that can form between the myosin and actin filaments in the sarcomere. More sarcomeres in parallel means there are more myosin heads available to bind to actin, which increases the number of cross-bridges that can form simultaneously, and as a result, the muscle generates more force.
For sarcomeres in series, how do they affect force production?
They dont, but they do increase the length. This arrangement allows the muscle to shorten over a greater distance during contraction.
List ways to modify force production
- increase # of working cross bridges
- add cross bridges in parallel
- inc # of myofibrils in parallel
- inc cross sectional area of muscle
What are the two passive properties
- stiffness: how resistent is the muscle to stretching. This protects against muscle strain/tearing
- elasticity: how well can muscles function as a spring. (go back to relaxed length easier)
What contributes to the stiffness/elasticity qualities of muscles for Extracecullar?
- made up of collagen which is the primary protein for stiffening
What contributes to the stiffness/elasticity qualities of muscles for intracellular?
structures called third filament - Titin protein.
its a molecular spring that’s easily extensive until it reaches half of 2.7 micrometer. so when sarcomere stretches the stiffness increases
- titin runs from z disc to m line
Discuss the passive force curve
2.0-2.2 is the ideal range.
2.7 is the max range of efficiency. Once you go past this, it becomes more stiff. Once you release, it’ll go back to the optimal length (this is that spring action)
discuss the velocity of unloaded muscles curve
- velocity of contraction only declines at 3.6 micrometers
- if you have longer lengths, you will have fewer cross bridges but its still moving at the same velocity as long as some cross bridges are touching.
