15.8 contraction of skeletal muscles

Question 1

what occurs to the sarcomere during the sliding filament mechanism?

Answer 1

• I-bands becomes narrower
• Z-line move closer/shortens
• A-bands remain same
• H-zones remain same

Question 2

explain the process of muscle stimulation. (3)

Answer 2

1- action potential reaches neuromuscular junctions simultaneously -> Ca2+ ion protein channels open & Ca2+ diffuse in synoptic knob
2- synaptic vesicles fuse with pre-synaptic membrane & release acetylcholine in synaptic cleft
3- acetylcholine diffuse across synaptic cleft & binds with receptors on muscle cell-surface membrane -> depolarisation

Question 3

describe the process of muscle contraction. (7)

Answer 3

1- action potential opens Ca2+ ion channels on sarcoplasmic reticulum & Ca2+ ions diffuse into muscle cytoplasm down conc. gradient
2- Ca2+ ions causes tropomyosin molecules to pull away from actin filament binding sites
3- myosin heads bind to actin filaments & form a cross-bridge
4- attached myosin heads change angle & pulls actin filament along, releasing ADP + Pi
5- ATP molecules binds to myosin head & causes it to detach from actin filament
6- Ca2+ ions activate ATPase & hydrolyses ATP -> ADP + Pi; the release energy causes myosin head to return to original position
7- myosin head reattaches along actin filament & repeats

Question 4

describe the process of muscle relaxation. (3)

Answer 4

1- Ca2+ ions actively transported back into sarcoplasmic reticulum using energy from ATP hydrolysis
2- reabsorption of Ca2+ ions allow tropomyosin to block action filaments
3- myosin heads are unable to bind to actin filaments & muscle relaxes
-> force from antagonistic muscles could pull actin filaments out from myosin

Question 5

what is phosphocreatine & when is it used?

Answer 5

reserve supply for ADP + Pi
- used in anaerobic respiration to generate ATP rapidly