13.10 Sliding Filament Model Flashcards
(19 cards)
What does the siding filament model describe
Muscle contraction
What do myosin and actin do during muscular contraction
Myosin filaments pull actin filaments inwards towards the centre of the sacromere
What happens to the light band and dark band during muscle contraction
Light band becomes narrower
Dark band remains the same width because myosin hasn’t shortened but just overlap the actin filaments
What happens to the z-line and H -zone in muscular contraction
Z line moves closer together - shortening the sacromere
H-zone becomes narrower
What is the structure of myosin
They have globular heads that are hinged so move back and forth
Tails are aligned to other myosin tails to form a myosin filament
What are attached to the globular heads of myosin
Binding sites for actin and ATP
What does actin have in relation to myosin globular heads
Binding sites for the heads - actin-myosin binding site
What blocks the binding sites in actin to myosin globular heads when in resting state
Tropomyosin which is held in place by troponin
What happens to actin binding sites and myosin globular heads when muscles are stimulated to contract
Myosin heads form bonds with actinmysoin cross bridges causing the myosin heads to flex in unison and pull the actin filaments along the myosin
What is a neuromuscular junction
The place where an action potential arrives and causes muscular contraction
It’s the point where the motor neurone and skeletal muscle fibre meet
What is a motor unit
All of the muscle fibres supplied by a single motor neurone
What happens to calcium
Ions when an action potential reaches a neuromuscular junction
The calcium ion channels are opened so calcium is released and diffuses into the synapse causing synaptic vesicles to fuse with membranes releasing acetylcholine (neurotransmitters) into the synoptic cleft
Acetylcholine then binds with receptors on the sarcolemma and open sodium ion channels causing depolarisation of the sarcolemma
What happens when an action potential causes the depolarisation of sarcolemma
The depolarisation travels deep into the muscle fibre by spreading through T-tubules which are in contact with the sarcoplasmic reticulum
What happens when the action potential reaches the sarcoplasmic reticulum after the depolarisation of the sarcolemma
Calcium ion channels are stimulated and release calcium ions into the sarcoplasm
The calcium binds to troponin
What happens to myosin and actin when calcium ions are released into the sarcoplasm
The calcium ions bind to troponin causing it to change shape and pull on tropomyosin causing it to stop blocking the actin myosin binding sites
Now actin myosin cross bridge is formed and the filament flexes and pulls actin along
How do myosin globular heads detach from actin
When filament heads flex ADP on myosin is released and ATP can now bind to myosin which causes the head to detach from actin
How do myosin heads return to their normal position
Calium ions activate ATpase activity of myosin which hydrolyses the ATP to ADP and phosphate
This releases energy which is then used by the myosin to return to normal postition
What is the energy supply that is needed in muscle contraction
When ATP is hydrolysed to ADP and phosphate
the movement of myosin heads
Sarcoplasmic reticulum to actively absorb calcium ions
How do scientists monitor muscle contraction
Use sensors to monitor the electrical activity in a muscle
They measure the strength of a contraction and track muscle fatigue levels
