muscle contraction Flashcards
what is skeletal muscle
the type of muscle you use to move, e.g. biceps and triceps
what to tendons do
attach skeletal muscle to bones
what do ligaments do
attach bones to other bones
how do bones work as levers
because bones are incompressible so they can act as a lever to give the muscle something to pull against
what are antagonistic pairs
muscles that work together, one muscle contracts and one muscle relaxes, the contracting one is called agonist and the relaxing one is called antagonist
give an example of how antagonistic pairs of muscles work
when your bicep contracts, your tricep relaxes and when your tricep contract your bicep relaxes.
what is the cell membrane of the muscle fibres called
sarcolemma
the muscle fibre membrane has folds on it, what are these called and what’s its purpose
transverse t tubules, they help spread the electrical impulse throughout the sarcoplasm so they reach all parts of the muscle fibre
what’s the network of internal membranes called and what’s its purpose
sarcoplasmic reticulum, stores and releases calcium ions which are needed for muscle contraction
what do muscle fibres have plenty of
mitochondria to provide ATP for contractions
muscle fibres are multinucleate, what does this mean
they have many nuclei
muscle fibres have long, cylindrical organelles, what are these called, what are they made of and what is their purpose
myofibrils, they’re made of proteins and are highly specialised for contraction
what 2 things do myofibrils contain in them and what are each of them made of
1) thick myofilaments made of the protein myosin
2) thin myofilaments made of the protein actin
if you look at a myofibril under a microscope what 2 things do you see, and are they called
1) dark bands that contain thick myosin myofilaments and some thin actin filaments - called A bands
2) light bands that contain thin actin filaments ONLY - called I-bands
myofibrils are made up of small units called what
sarcomeres
what marks the middle and end of each sarcomere and what does the middle also mark
middle - M-line. the m-line is also the middle of the myosin filaments
end - Z-Line
what is around the middle line of the sarcomere and what does this contain
H-zone, the H-Zone only contains myosin filaments
what slides over one another to make the muscle contract
the myosin and actin filaments slide over each other to make the sarcomeres contract, the actual myofilaments don’t contract themselves
what does the simultaneous contraction of lots of sarcomeres mean
the myofibrils contract which means the muscle fibres contract
myosin filaments have globular heads, what does this mean
this means they’re hinged so they can move back and forth
what 2 things does each myosin head have
1) binding site for actin
2) binding site for ATP
what do actin filaments have on their surface and what are they called
binding sites for myosin heads called actin-myosin binding sites
what is found between actin filaments and what does it help
a protein called tropomyosin which helps myofilaments move past each other
in resting muscles what blocks the actin-myosin binding site and what does this mean
the actin-myosin binding site is blocked by tropomyosin which means myofilaments cannot slide past each other because the myosin heads cant bind to the actin-myosin binding site
how is a muscle contraction triggered by an influx of calcium ions (5 steps)
1) when depolarization spreads down the T-tubules is causes the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm
2) these bind to a protein attached to tropomyosin, causing the protein to change shape which pulls the tropomyosin out of the actin-myosin binding site and exposes the binding site which allows the myosin head to bind
3) the bond formed is called actin-myosin cross bridge, calcium ions also activate the ATP hydrolase which hydrolyses ATP into ADP and Pi to provide energy, this energy causes myosin head to bend, which pulls the actin filament in a rowing action
4) another ATP molecule provides energy to break the actin-myosin cross bridge so the myosin head detaches and then reattaches to a different binding site further along the actin filament so a new cross bridge is formed and the cycle is repeated
5) many cross bridges form and break very rapidly which pulls the actin filament along which shortens the sarcomere causing the muscle to contract, this cycle will keep happening as long as calcium ions are present
what happens in terms of calcium ions when the muscle stops being stimulated, what does this cause and why does this mean muscles aren’t stimulated anymore
when the muscle stops being stimulated the calcium ions leave their binding sites and move back by active transport into the sarcoplasmic, this causes tropomyosin molecules to move back, so they block actin-myosin binding sites so the muscles aren’t contracted because no myosin heads are attached to actin filaments
what are the 3 ways ATP is generated when muscles are contracted
1) aerobic respiration
2) anaerobic respiration
3) ATP-Phosphocreatine system
how does the PCr system work (3 steps)
1) ATP is made by phosphorylating ADP by adding a phosphate group taken from PCr
2) PCr is stored inside cells and the ATP-PCr system generates ATP very quickly
3) PCr runs out after a few seconds so its used in short bursts of exercise
4) the ATP-PCr system is anaerobic and its alactic
