Muscle Contraction

Question 1

What are the 3 main types of muscle in body and which is under conscious control?

Answer 1

• cardiac; in heart
• smooth; in walls of blood vessels and gut
• skeletal; under voluntary control

Question 2

Why is muscle contraction efficient?

Answer 2

• small muscle fibres (myofibrils) are grouped together and lined up parallel to each other, to maximise strength
• made of smaller units grouped together
• if muscle was made up of individual cells, junctions between cells would be a point of weakness, why muscle fibres share nuclei and sarcoplasm

Question 3

What does the Anisotropic band in muscle contain?

Answer 3

• overlapping actin and myosin fibres

Question 4

What is the structure of actin?

Answer 4

• thinner than myosin

- made up of 2 strands wrapped round each other

Question 5

What adaptations do slow twitch muscle fibres have?

Answer 5

• large store of myoglobin (red molecule that stores oxygen)
• numerous mitochondria for aerobic respiration
• rich supply of blood vessels
• supply of glycogen

Question 6

What adaptations do fast twitch muscle fibres have?

Answer 6

• many enzymes associated with anaerobic respiration
• store of phosphocreatine (synthesises ATP from ADP in anaerobic conditions)
• thicker and more numerous myosin filaments

Question 7

Why are there many neuromuscular junctions spread throughout the muscle?

Answer 7

• contraction is rapid and simultaneous

Question 8

Explain how nerve impulses cross neuromuscular junctions

Answer 8

1. Action potential is recieved at junction
2. Synaptic vesicle fuses with precision-synaptic membrane and release neurotransmitter into cleft
3. Binds to receptor sites on post-synaptic membrane, causing rapid influx of Na+
4. Membrane is depolarised

Question 9

What is the evidence for the ‘Sliding Filament Mechanism’?

Answer 9

• I bands shorten
• H zones narrow
• sarcomeres shorten

Question 10

What impact do calcium ions have on muscle contraction?

Answer 10

• calcium ions flood into muscle cytoplasm cause the tropomyosin molecules blocking the binding sites on actin filament to move away

Question 11

Describe process of muscle contraction

Answer 11

1. Calcium ions cause tropomyosin molecules to move away from binding sites on actin
2. Myosin head attaches to binding site and changes angle, releasing ADP and moving actin filament along
3. ATP molecule fixes to head, causing it to detach
4. ATP is hydrolysed to ADP by ATPase, giving energy for head to return to normal position

Question 12

What is energy required for in muscle contraction?

Answer 12

• movement of myosin heads

- reabsorption of calcium ions from endoplasmic reticulum

Question 13

Why is phosphocreatine needed?

Answer 13

• ATP needs to be generated in anaerobic conditions, when there is not an immediate source of oxygen, allows rapid muscle contraction