whats molecular composition of myofilaments
other proteins help form the structure of the myofibril - also maintains alignment of sarcomere
what 3 things consist in molecular composition of myofilaments
Elastin filament dystrophin nebulin
Elastin filament
composed of protein titin -holds thick filaments in place; helps recoil after stretch; resists excessive stretching
Dystrophin
links thin filaments to proteins of sarcolemma
Nebulin
myomesin, C proteins binf filaments or sarcomeres together
Whats the sarcoplasmic reticulum
network of smooth endoplasmic recticulum tubules surrounding each myofibril
list 4 things about the sarcoplasmic recticulum
-most run longitudinally -terminal cisterns form perpedicular cross channels at the A-I band junction -SR functions in regulation of intracellular levels -Stores and releases calcium
what are t tubules
tube formed by protrusion of sarcolemma deep into cell interior - penetrate cell’s interior at each A-I band junction between terminal cisterns
what do t tubules do
increase muscle fiber’s surface area greatly lumen continous w/ extracellular space allow electrical nerve transmissions to reach deep into interior of each muscle fiber
Triad
area formed terminal cistern one sarcomere, T tubule, and terminal cisterns of neighboring sarcomere
whats a triad relationship
when an electrical impulse passes by, T tubule proteins change shape, causing SR proteins to change shape, causing release of calcium into cytoplasm
contraction
the activation of cross bridges to generate force
shortening
occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening
contraction ends
when cross bridges become inactive
what happens in the relaxed state
thin and thick filaments overlap only slightly at end of A band
describe a Sliding filament
model of contraction stares that during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more
in sliding filaments what doesnt change length
neither thick nor thin filaments change length, just overlap more
what occurs in the nervous system that causes contraction
when the nervous system stimulates muscle fiber, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) to begin
what happens when cross bridge attatchments form and break several times?
each time oulling thin filaments a little closer toward center of sarcome in a ratcheting action -causes shortening of muscle fiber
name which bands and lines are pulled together in contraction
Z discs are pulled toward M line I bands shorten Z discs become closer H zones disappear A bands move closer to each other
just look at the gif
just look at it
just look at it
just look at it