alright..... its muscle activation time Flashcards
How is the cross bridge formed?
Calcium is released into the sarcoplasm and binds to a subunit of troponin. The binding of Ca to troponin causes a change in shape of tropomyosin which roles out of the way and exposes the myosin binding site on the actin. They can now have molecular interactions, and the CROSS bridge is formed when myosin binds with actin.
What happens after the cross bridge is formed (e.g. how is the power stroke formed)
ADP and Pi are released from the myosin head which causes a shape change in the myosin head and it flexes which still bound to actin (power strokes).
What results from the power stroke?
The power stroke results in a tiny shift in the position of the thick and thin filaments and the ends of the sarcomere are pulled towards one another.
How is the cross bridge broken after the power stroke?
The ATP binding site is exposed and ATP binds to the myosin head. This binding lowers the affinity of myosin for actin and it detaches, the cross bridge is now broken.
How does the myosin head become ‘re-cocked’?
The myosin ATPase hydrolyses the ATP to ADP + Pi and the myosin head is re-cocked in the readiness for another cycle. The cycle is repeated as long as Ca and ATP are present.
How much does the cross bridge cycle take place?
Millions of times at billions of cross bridges with each contraction.
What happens to the Ca after the contraction is fully finished?
It is pumped back into the sarcoplasm by the Ca pump which pumps it against its concentration gradient.
What is a twitch?
A single action potential will result in the release of a pulse of Ca into the sarcoplasm and short period of tension development will ensure.
What is a tetanus?
Many action potentials fired in rapid sequence results in a sustained release of Ca from the SR, a sustained period of actin myosin interaction and thus a sustained period of contraction.
