13.10 Sliding Filament Model

Question 1

What does the siding filament model describe

Answer 1

Muscle contraction

Question 2

What do myosin and actin do during muscular contraction

Answer 2

Myosin filaments pull actin filaments inwards towards the centre of the sacromere

Question 3

What happens to the light band and dark band during muscle contraction

Answer 3

Light band becomes narrower

Dark band remains the same width because myosin hasn’t shortened but just overlap the actin filaments

Question 4

What happens to the z-line and H -zone in muscular contraction

Answer 4

Z line moves closer together - shortening the sacromere

H-zone becomes narrower

Question 5

What is the structure of myosin

Answer 5

They have globular heads that are hinged so move back and forth
Tails are aligned to other myosin tails to form a myosin filament

Question 6

What are attached to the globular heads of myosin

Answer 6

Binding sites for actin and ATP

Question 7

What does actin have in relation to myosin globular heads

Answer 7

Binding sites for the heads - actin-myosin binding site

Question 8

What blocks the binding sites in actin to myosin globular heads when in resting state

Answer 8

Tropomyosin which is held in place by troponin

Question 9

What happens to actin binding sites and myosin globular heads when muscles are stimulated to contract

Answer 9

Myosin heads form bonds with actinmysoin cross bridges causing the myosin heads to flex in unison and pull the actin filaments along the myosin

Question 10

What is a neuromuscular junction

Answer 10

The place where an action potential arrives and causes muscular contraction
It’s the point where the motor neurone and skeletal muscle fibre meet

Question 11

What is a motor unit

Answer 11

All of the muscle fibres supplied by a single motor neurone

Question 12

What happens to calcium

Ions when an action potential reaches a neuromuscular junction

Answer 12

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

Question 13

What happens when an action potential causes the depolarisation of sarcolemma

Answer 13

The depolarisation travels deep into the muscle fibre by spreading through T-tubules which are in contact with the sarcoplasmic reticulum

Question 14

What happens when the action potential reaches the sarcoplasmic reticulum after the depolarisation of the sarcolemma

Answer 14

Calcium ion channels are stimulated and release calcium ions into the sarcoplasm
The calcium binds to troponin

Question 15

What happens to myosin and actin when calcium ions are released into the sarcoplasm

Answer 15

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

Question 16

How do myosin globular heads detach from actin

Answer 16

When filament heads flex ADP on myosin is released and ATP can now bind to myosin which causes the head to detach from actin

Question 17

How do myosin heads return to their normal position

Answer 17

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

Question 18

What is the energy supply that is needed in muscle contraction

Answer 18

When ATP is hydrolysed to ADP and phosphate
the movement of myosin heads
Sarcoplasmic reticulum to actively absorb calcium ions

Question 19

How do scientists monitor muscle contraction

Answer 19

Use sensors to monitor the electrical activity in a muscle

They measure the strength of a contraction and track muscle fatigue levels