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Muscle Cell actoin potential
A brief change in muscle cell voltage from negative to positive to negative. (normal is negative)
True or False: Muscle cell action potetial, travels along the suface of muscle cells very quickly, probably more thea 100 m/sec or about the speed of and Indy reacecar.
Remember that skeletal and __________ muscle have a series of _________ _________ (T tubules) that help the action potential penetrate deep into the muscle ________.
cardiac, trasnvers tubules, fiber
From Action ptential to Calcium release
- Muscle cell action potenial travels along muscle surface
- Penetrates into the interior of the muscle cell at transvers tubules
- Remember T tubules arein a triad with two sacs of sarcoplaspic reticulum
- Sarcoplasmic reticulum releases calcium into the cytoplasm of the muscle cell
From Calcium Release to contraciton
Calcium released from SR them binds to troponin; this moves tropomyosin aside and exposes binding sites for myosin on the actin filament
True or False : The calcium released from the sarcoplasmic reticulum interacts with a special protien, found only in muscle cells
When calcium binds to the protein called troponin...
...it changes shape, and pushes another specialized protien called tropomyosin
- "moving muscle protein"
- normally covers a myosin binding site ont e actin molecule
- keeps myosin (which wants to bind actin) from being able to reach its binding site on actin.
When _________ is present, and troponin shoves topomyosin and topomyosin moves away from the _______ ______, myosin can grab _______.
calcium, binding site, actin
True or false : Stereograms don't work when projected on a screen.
see objective 14 p.446- 447
The cross-bridge cycle
- 6a. calcium binds to troponin; troponin choves tropomyosin; tropomyosin moves, exposing the myosin binding site on actin.
- 6b. Myosin brings a piggy backed molecule of ATP which is split to form ADP and the loose phosphate is released as myosin binds actin
- 6c. Power stroke: the shape of myosin changes; the head region flexes and moves the actin filament a tiny amount. this releases ADP and opens a site for ATP to bind again
- 6d. ATP binds, myosin release the actin filament, and the cycle can begin agian.
- A dead person uses up their ATPin a matterof minutes ore hours depending on the temperature, and muscles are "locked" in position
- Later, again cepending on temperature , cirobes break down muscle tissue to the point where muscle becomes loose again.
What happens if ATP is absent from the cross-bridge cycle?
- Myosin remains permanently bound to actin, muscles cannot move
- -miuscle stuck between step 5 and 1
- Rigor motis results
- Eventually , ensymes and microbes destroy muscle structure and corps becomes "loose" again.
How does a muscle cell kick back and relax for a while? (Relaxation)
- Calcium is pumped back intgo sarcoplasmic reticulum
- When calcium is absent toponin-tropomyosin slides back and covers myosin binding site on actin filament
- No cross-bridges are formed; muscle relaxes
- Some important features
- -action potentials are all-or-none; either they happen or they don't
- -if enough ACh is released, the muscle action potential which results always spreads over the entire surface of the muscle
- -the entire muscle cell contracts at once and it always contracts "all the way"
True or False : The process of excitation-conteaction coupling would not result in muscle contraction if actin andmyosins filaments were not percisely aligned in skeletal and cardiac muscles.
Because they are, exitation leads to contraction throu shortening the sarcomere.
True or False: Myosin molecules are held in a bundle by the protien titin, with the heads sticking out where they can interact with actin
The sliding filament model
- As myosin head flex, they move actin filaments
- As actin filaments move, the Zlines are brought together and the sarcomeres shortens
- As thousands of sarcomers shorten, the entire muscle fiber shortens
- As muscle fibers shrten, the muscle contracts