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BIO 2310 - Exam 3 (Muscles) > Myofilaments > Flashcards

Flashcards in Myofilaments Deck (12):

anatomy of sk mm

-multi nucleated - below plasma membrane is the sarcolemma which is where the oval nuclei can be seen - dark nuclei lay adj to myofibrils - alternating light (I) bands and dark (A) bands that give the striped appearance



myofibrils are chains of these contractile units

aligned end to end like coke cans

are between the two z lines



actin (thin filament) + myosin (thick filament, protein)

- contains ATPase which wil lsplit ATP to generate power for mm contraction

- thick filmaent is the length of the dark A band

- myosin contains the heads of the cross bridges



thin filaments

contractile protein

aids in preventing contractions (the heads of myosin)

anchored to the Z disc


contraction process

when it occurs:

1. actin filaments slide toward each other into the center of the sarcomere

2. the H zone or bare zone disappear bc the actin and mysoin are completely overlapped


sacroplasmic reticulum

surrounds each myofibril (like a sleeve of loosely crocheted sweater material around your arm)

F: store and release Ca when the mm fiber is stimulated to contract


Sliding Filament Theory

MM contraction (filaments are actin and myosin, myson has the ehads like an oar in boat)

1. electrical signal is sent, heads will attach to the binding sites of thin actin filaments

2. creates sliding mechanism

3. ATP supplies the energy, allowing pulling mechanism of thin filaments toward the center of the sacromere

4. goes on simultaneously in sarcomeres through out the cell adn mm cell shortens


role of Ca in mm contraction

1. attachment of myosin heads to actin require Ca

2. AP stimualtes the SR to release Ca (where it is stored) into cytoplasm

3. Ca trigger the binding of myosin to actin, initiates sliding

4. AP ends, Ca absorbed into SR storage, mm relaxes and goes back to original length

happens in few thousands of a second


length of zones in contractions

A zones get closer together, but they do not change in length

light H zone in centre dissapears, Z discs are closer to thick filaments, I bands dissapered


myosin heads binding

heads cocked like hammer to gun or mouse trap

ATP allows for cock to recock (like crew team)

myofilaments do NOT shorten, just glide past each other

Troponin tropomyosin aid in "unnecessary contraction:" they cover the actin and are untwisted for contraction


T tubules and troponin/tropomyosin

transverse tubules that are extensions of the cell membrane that penetrate into the centre of skeletal and cardiac muscle cells

F: conduct impulses from surface of the cell (sarcolemma) down into the SR

creates opening for AP to travel in cell to SR

- Ca ions bring to troponin, troponin changes shape, removing blocking action of tropmyosin, actin active sites exposed


z line

formed btw adj sacromeres, where thin actin filaments attach