muscle 1 Flashcards
what is muscle attached to
tendons on either side of joint then tendons attached to bones
what do stripes indicate
underlying molecular mechanisms that enable muscle fiber to contract
what are muscle fibers generated from
Muscle fibers are generated during development by the fusion of a large number of small precursor cells called myoblasts. Each myobast has a single nucleus, whereas the fiber is a multinucleated cell.
why is it good that muscle fiber is long and thin and mutilnucleated
long and thin = muscles make lots of proteins that fill up fiber and is responsible for contraction
sites of mrna synthesis all down length of muscle fiber = enables proteins to be synthesized locally all down length of fiber (more genes copies = more proteins it can make)
describe myofibrils
make up skeletal muscle fibers
made of protein
dark and light stripes lined up together = molecular machinery
what does myofibrils lined up together cause
allows fiber to contract as single unit, maximizes amount of force and efficiency
describe bands or lines of sarcomere
i band = light
each i band = z line in middle
a band = dark
describe how contract
sarcomere contract = myofibrils contract = muscle fiber contracts = muscle contracts
describe filaments of sarcomere
thick filaments extending from one end of the A band to the other
thin filaments, attached to the Z lines and extending across the I band-and part way into the A band
describe cross bridges
part of thick filaments = interact with thin filaments and causes muscle to contract
describe distribution of thick and thin filaments in sarcomere
thick = each surrounded by halo of 6 thin
thin = surrounded by 3 thick
matrix of thin and thick - crystalline arrangement
what is in i band
thin = actin
what is h zone
only think
what is a band
overlap of thick and thin filaments
overlap = critical for contraction of muscle
describe thin filaments
actin - 2 chains of globular actin subunits twisted into helix
sticks to itself and forms long thin fiber
describe thick filaments
myosin
forms long thin filament with head
bundles = thick filament
bundles attached together tightly = m line
describe sliding filament model
head groups of thick reach out and gab thin and pull over thick = pulls z lines closer together and they let go and then pull again = cycle
head groups act independently = has no idea what other groups are doing - all are in diff phases of cycle
driven by atp hydrolysis
do thin and thick filaments change in length
nO
stay same but overlap becomes greater
Contraction of sarcomeres
shortens entire myofibril
what does the amount of tension a muscle fiber can develop depend on
fiber length
length-tension relation reflects degrre of overalp between thick and thin filaments
describe length-tension ratio
too contraction = muscle fiber runs into z lines = has no place to go
optimal range
no overlap = no contraction, too spread out, like lift something heavy and arms stretched out
holding something heavy in place - myosin head groups reach out and grab actin and pull but are not getting anywhere and keeps happening, thin filaments not moving, since being pulled apart as strongly as they are being pulled together by head group