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Unformatted text preview: iculum. Nerve signals carried DEEPLY into muscle ﬁber by T-Tubules, causes
calcium ion release from Sarcoplasmic reticulum. Fig. 10-11 JUST READ OVER THIS
AND GET A GENERAL IDEA. Ca2+ ions bind to troponin,
moving tropomyosin to expose the
sites on actin that interact with the
myosin heads. Myosins bind ATP
and pivot, pulling actin filament
along thick filament. ATP breaks
down and myosins detach, then
attach again to other G-actins
farther along thin filament.
Repeating this cyclically causes
contraction. When the muscle is relaxed (top), the
I bands and sarcomeres themselves are
at their widest.
SARCOMERE SHORTENS WHEN FILAMENTS SLIDE
PAST EACH OTHER -- BUT LENGTH DOESNT CHANGE! TITIN - LARGEST PROTEIN IN CELLS -- AUTOMATICALLY PULLS
FILAMENTS BACK TO THEIR STARTING POSITION DURING
RELAXATION? In a partially contracted muscle, the I band
and sarcomere are shorter (narrower). In a fully contracted muscle, the sarcomere
is at its shortest and the I bands disappear. Fig. 10-12 Through these changes, the actual length
of the thick & thin fila...
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- Spring '14