MUSCLE CONTRACTION Flashcards
what are the 2 types of muscle fibres
type 1
type 2
Describe the events of a muscle contraction
Action potential arrives at a neuromuscular junction
Neurotransmitter diffuses across gap and opens gated Na+ channel
Wave of depolarisation triggers calcium to be released from the sarcoplasmic reticulum by opening calcium ion channel and therefore diffuse out (low calcium in cytoplasm)
Calcium binds to tropomyosin causing it to change shape and expose myosin binding sites on actin
ADP attaches to myosin head = powerstroke
ATP attaches to myosin head = causing it to detach
Calcium activates ATPase which hydrolyses ATP–> ADP therefore providing energy for myosin to return to original position.
ADP reattaches and mason attaches further down actin filament
How are muscles attached to bones
tendons
What attaches bone to bone
ligaments
what is the agonist
the contracting muscle
what is the antagonist
the relaxing muscle
what are skeletal muscle fibres made up of
large bundles of long cells called muscle fibres
Look STRIATED due to alternating dark and light bands
what is the sarcolemma
the cell membrane of muscle fibres
What is the sarcoplasm
a muscle cells cytoplasm
what are the folds called that stick into the cytoplasm
T tubules
What is the function of a T tubule
help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
what is the sarcoplasmic reticulum
a network of internal membranes that runs through the sarcoplasm
what is the function of the sarcoplasmic reticulum
stores and releases calcium ions that are needed for muscle contraction
wha organelle do muscles have lots of and why
mitochondria for aerobic respiration
a muscle fibre is multinucleate- what does that mean
it has many nuclei
what do muscle fibres have lots of
long cylindrical organelles called myofibrils
made up of proteins and highly specialised for contraction
what 2 filaments do myofibrils contain
thick myosin filaments
thick actin filaments
what does a myofibril look like under an electron microscope
alternating dark and light bands
dark bands - thick myosin filaments, and some overlapping thin actin filaments
light bands - thin actin filaments ONLY
what are the dark bands called
A bands
what are the light bands called
I bands
what is each myofibril made up of
many short units called sarcomeres
what is at the end of each sarcomere
a Z line
what is in the middle of each sarcomere
an M line
The M line is the middle of the myosin filaments
What is the H zone
The H zone is around the M line and only contains myosin filaments
Explain the sliding filament theory
Myosin and actin filaments slide over one another to make the sarcomeres contract
The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
Sarcomeres return to their original length as muscle relaxes
what changes occur when the sarcomeres contract
A bands stay same length
I bands get shorter
H zones get shorter
Sarcomeres get shorter
What do myosin filaments have
globular heads that are hinged so can move back and forth
binding sites - one for actin and one for ATP
what do activists filaments have
a binding site for myosin heads called an actin-myosin binding site
what protein is found between actin filaments and what does it do
tropomyosin
it helps filaments move past each other
what happens to the binding sites in resting muscles
the binding sites in resting muscles are blocked by tropomyosin
what happens to calcium when the muscle stops being stimulated
when muscle stops being stimulated
calcium ions leave their binding sites and are moved back to sarcoplasmic reticulum via active transport
This causes the tropomyosin to move back too
So they block the bonding sites
Actin filaments slide back to their relaxed position which lengthens the sarcomere
what is it called when the myosin head is attached to the actin filaments
a cross bridge
ATP-PC system, how long does PC last
a few seconds
state some properties of slow twitch muscle fibres
endurance activites can work for a long time without fatigue energy released slowly aerobic respiration lots of mitochondria red in colour as rich in myoglobin (red coloured protein that stores oxygen)
state some properties of fast twitch muscle fibres
used for fast movement short bursts of energy - speed or power get tired very quickly anaerobic respiration less mitochondria fatigue quickly due to lactic acid white in colour as less myoglobin (so can't store much oxygen)
