muscle contractions 2 Flashcards
What is a network of internal membranes that runs through the sarcoplasm called
The sarcoplasmic reticulum
What does the sarcoplasmic reticulum do
The sarco plasmic reticulum stores and rele ases calcium ions that are needed for muscle contraction
What do muscle fibres contain alot of
M uscle fibres have lots of mit ocho ndria to provide
the ATP that’s needed for muscle contraction.
What is multinucleate
M uscle fibres are multinuclea te (contain many nucle i).
What are myofibrils
M uscle fibres have lots of long, cylin drical organelles c alle d myofibrils. They’re made up of proteins and are highly sp ecialised for co ntraction.
What do myofibrils contain
Myofibrils Contain Thick Myosin Filaments and Thin Actin myofilaments hat move past each other to make muscles co ntract
What are thick myofuilaments are made of
Thick myofilaments are made of the protein myosin.
What are thin filaments made of
Thin myofilaments are made of the protein actin
If you look at a myofibril under an electron microscope what will you see
If you look at a myofibril under an electron microsco pe, yo u’ll see a pattern of alternating dark and light bands:
When looking at myofibril under an electron microscope what are the dark bands mad eof
Dark bands contain the thick myosin filaments and some overlapping thin actin filaments — these are calle d A-band
f you look at myofibril under a microscope what are the light bands made of
Light bands contain thin actin filaments o nly — these are calle d I-bands
What is a myofibril made up of
A myofibril is made up of many short units calle d sarcomeres., A myofibril is made up of many short units calle d sarcomeres.
What is the sliding filament theory
The theory explaining muscle contraction,
Myosin and actin filaments slide over one another to make the sarcomeres contract — the myofilaments themselves don’t contract. the myofilaments themselves don’t contract. The simultaneous contractio n of lots of sarcomeres means the myofibrils and muscle fibres contract. Sarcomeres return to their original length as the muscle relaxes.
What do myosin filaments contain
Myosin filaments have glo bular heads that are hinged, so they can move backand forth. 2) Each myosin head has a binding site for actin and a binding sit e for ATP.
What do actin filaments contain
Actin filaments have binding sites for myosin heads, calle d actin-myosin binding sites
What is tropomyosin and what does it do
Another protein calle d tropomyosin is found between actin filaments. It helps myofilaments move past each other.
What does tropomyosin block
Binding Sites in Resting Muscles are Blocked by Tropomyosin. ) So myofilaments can’t slide past each other because the myosin heads
can’t bind to the actin-myosin binding site on the actin filaments.
What is muscle contraction triggered by
Influx of calcium ions
What happens when an action potential from a motor neurone stimulates a muscle cell
it depolarises the sarcolem ma. Dep olarisation spreads down the T-tubules to the sarco plasmic reticulumThis causcs the sarco plasmic reticulum to release stored ca lciu m ions (Ca2+) into the sarcoplasm.
What do calcium ions bind to
Ca lcium ions bind to a protein attached to C a * binds to a protein, which moves tropomyosin myosin he a d_ binds to the exposed site actin-myosin cross bridge formed tropomyosin, causing the protein to change shape. This p ulls the attached tropomyosin out of the actin-myosin binding site on the actin filament. This ex poses the binding site, which allows the myosin head to bind
What is an actin myosin cross bridge
The bond formed when a myosin head binds to an actin filamen t
What do calcium ions also activate
Calcium ions also activat e the enzym e ATP hydrolase which hydrolyses (breaks d own) ATP (into A D P + P;) to provide the energy needed for muscle contraction.
What does the energy released from ATP cause
The energy released from ATP causes the myosin head to bend, which pulls the actin filament along in a kind of rowing action.
How does the myosin head detach from the filament after its moved
Another A TP m ole cule provides the energy to break the actin-myosin cross bridge, so the myosin head de taches from the actin filament after it’s moved.
What does teh myosin head reattach to after detaching from the actin filament
The myosin head then rea ttaches to a different binding site further along the actin filament. A new actin-myosin cross bridge is formed and the cycle is repea ted (attach, move, detach, reattach to new bin din g site
What exactly causes the muscle to contract
Many cross bridges form and break very rapidly, pulling the actin filament along — which shortens the sarcomere, causing the muscle to contract 11) The c yc le will co ntinue as long as calciu m ions are present.
