Muscles

Question 1

Where is the : A band, I band, H zone and Z line?

Answer 1

Question 2

Where is the A band located? How does this change in contraction?

Answer 2

location of myosin [no change in contraction]

Question 3

Where is the I band located? How does this change in contraction?

Answer 3

location between the myosin [shortens in contraction]

Question 4

Where is the H zone located? How does this change in contraction?

Answer 4

location between the actin [shortens in contraction]

Question 5

Where is the Z line located? How does this change in contraction?

Answer 5

end line of sarcomere [moves closer together in contraction]

Question 6

Role of Ca2+ ions and ATP in muscle contraction?

Answer 6

• Ca2+ ions causes the tropomyosin to move exposing binding sites on actin
• Ca2+ ions stimulate ATPase
• ATP causes myosin head to detach
• ATP releases energy so myosin head returns to original position
• ATP actively transports Ca2+ ions into sarcoplasmic reticulum when the muscle is relaxed

Question 7

What occurs in the first part of the sliding filament mechanism?

Answer 7

• the myosin heads pull the actin inwards
• the somatic motor neurone connects to the skeletal muscle via a neuro-muscular junction
• one motor neurone connects to a few muscle fibres = motor unit
• releases acetylcholine that binds to complementary receptors on the muscle fibre membrane (sarcomere)

Question 8

What occurs in the second part of the sliding filament mechanism?

Answer 8

• Na+ channels open, Na+ ions enter the muscle fibre causing depolarisation
• wave of depolarisation travels thru sarcoplasmic reticulum
• causes release of Ca2+ ions into the sarcoplasm
• this moves the tropomyosin on the actin

Question 9

What occurs in the third part of the sliding filament mechanism?

Answer 9

• exposes binding sites on the actin
• myosin heads now bind to the actin (cross bridge)
• a power stroke occurs, the myosin pulling the actin inwards
• ATP attaches to myosin head so it detaches

Question 10

What occurs in the fourth part of the sliding filament mechanism?

Answer 10

• ATP brokendown by ATPase to release energy
• myosin head goes back to its original position
• so it reattaches, pulling the actin further inwards

Question 11

How does fast twitch muscle fibres work?

Answer 11

• provide powerful but short lasting contractions
• found in biceps and sprinters
• has thicker myosin
• contains more enzymes for anaerobic respiration
• contains phosphocreatine, provides phosphate to ADP to reform ATP

Question 12

How does slow twitch muscle fibres work?

Answer 12

• provide less powerful but long lasting contractions
• found in thigh and marathon runners
• adapted for aerobic respiration
• has a rich blood supply
• contains many mitochondria
• contains glycogen
• contains myoglobin (stores oxygen)