6: Muscle Contraction

Question 1

Myosin filaments structure?

Answer 1

Have hinged globular heads that can move back and forth, each head has a binding site for actin and a binding site for ATP

Question 2

What happens when an action potential stimulates a muscle cell?

Answer 2

Depolarises the sarcolemma, depolarisation spreads down the T-tubules to the sarcoplasmic reticulum, releases calcium ions into the sarcoplasm

Question 3

Actin filaments structure?

Answer 3

Have actin-myosin binding sites, have tropomyosin between actin filaments that blocks the binding sites when the muscle is resting

Question 4

What do the calcium ions do?

Answer 4

Bind to a protein (troponin) attached to tropomyosin, causing it to change shape, pulls the tropomyosin out of the actin-myosin binding sites, allowing the myosin heads to bind - forms actin-myosin cross bridge

Question 5

What enzyme do the calcium ions activate?

Answer 5

ATP hydrolase - energy released causes the myosin head to bend, which pulls the actin filament along

Question 6

What causes the actin-myosin cross bridge to break?

Answer 6

An ATP molecule

Question 7

How are calcium ions returned to the sarcoplasmic reticulum?

Answer 7

Active transport

Question 8

ATP-phosphocreatine system features?

Answer 8

Can regenerate ATP very quickly, runs out quickly, anaerobic, alactic

Question 9

What is creatine broken down into?

Answer 9

Creatinine, removed by the kidneys

Question 10

Slow twitch muscle fibres features?

Answer 10

Contract slowly, high resistance to fatigue, aerobic respiration, lots of mitochondria, lots of blood vessels, rich in myoglobin (reddish)

Question 11

Fast twitch muscle fibres features?

Answer 11

Contract quickly, low resistance to fatigue, anaerobic respiration, PCr stores, few mitochondria, few blood vessels, not much myoglobin (whitish)