contraction of a muscle Flashcards
what cannot muscles do/ can do
they cannot push they can only pull
so what does this mean
muscles work in antagonistic pairs
what is the evidence for the sliding mechanism theory
the I band gets narrower and the h zone become narrower and the z lines move closer but a band remain same length
why does a band remain the same length
as this s determined by the length of the myosin filaments which hasn’t become smaller
what is myosing made out of
two protiens
what is the fibrous protein
arranged in a filament made up of several hundred molecules the tails
what is the globular protein
formed into two bulbous structures the heads
what is actin
a globular protein whose molecules are arranged into a long chain that twisted around to form a helical strand
what is tropomysin
form long thin sthreads that wrap around actin
what happens when an action potential reaches the neuromuscular junction
it reaches the junction simultaneously causing calcium ion channels to open and cause calcium ions to flow in and cause the synaptic vescicle to fuse with the pre synaptic membrane releasing the acetyl choline nto the synapse
what does acetyl choline do
diffuse and bind to the receptors found on the membrane of the muscle fibres causing it to depolarise
what happens to the action potential
travel deep into the fibre through a system of tubules
what are t tubules
extentions of the cell surface membrane and branch throughout the cytoplasm of the muscle
what are the tubules in contact with
the endoplasmic reticulum
what has the endoplasmic reticulum done
actively transported calcium ions from the cytoplasm into the er leading to very low concentration of ca + ions in the sarcoplasm
what does the action potential do next
open the calcium ion channel on the endoplasmic reticulum and calcium ion diffuse into the sacroplasm down a concentration gradient
wha tdoes the calcium ions do
cause the tropomyosin that were blocking the binding site on the actin filament to pull away
what happens when atp hydrolyses
the atp hydrolyses transferring energy and the adp ataches to the myosin head so they are in a state to bind to the actin filament and form cross bridges
what happens once attached
the myosin head changes their angle pulling the actin filament along releasing a molecule of adp
what does atp do
it attaches to the myosin head causing it to be detached from the actin filament
what does the calcium ions
activate the enzyme atpase which hydrolyses atp to adp and provide energy for muscle contraction
what does this provide energy for
atp is now adp attatched to the myosin head straightens the myosin head and return it to the original position
what then happens to the myosin head
as it is attached with an adp molecule it attaches to an actin binding site further along
how long is it repeated for
as long as the concentration of the calcium ions remain high
