Muscles

Question 1

Describe and explain the distinctive banding pattern in a relaxed and contracted sarcomere

Answer 1

• The darkest region is the myosin and action overlapping (A band)
• The light grey region is myosin only (H zone)
• The lightest/white region is actin only (I band)
• When the muscle contracts, H zone will get shorter, I band will get shorter, A band will stay the same and Z lines move closer together

Question 2

Outline the role of phosphocreatine in providing energy for contraction

Answer 2

It donates a phosphate to reform ATP quickly from ADP and Pi in anaerobic conditions
When the muscle relaxes, the creatine is phosphorylated back to phosphocreatine using Pi from ATP made in respiration

Question 3

Contrast slow and fast muscle fibres

Answer 3

Contrast;
- Slow fibers are adapted for aerobic respiration (long term/low intensity) whereas fast fibers are adapted for anaerobic respiration (short term/high intensity)
- Slow fibres contract more slowly with less powerful contractions whereas fast fibres contract rapidly with short powerful contractions
- Slow fibres have a large store of myoglobin whereas fast fibres don’t
- Fast fibers have a large store of glycogen whereas slow fibers don’t
- Slow fibres have more mitochondria than fast fibres

Question 4

Describe the 2 types of filament found in a muscle

Answer 4

Actin filaments are thin and made of actin plus tropomyosin
Myosin filaments are thick and made of many myosin molecules. Each myosin is made of a tail and head

Question 5

Describe the stages of myofibril contraction

Answer 5

1. action potentials depolarize the sarcolemma and T-tubules
2. voltage gated Ca2+ ion channels on the sarcoplasmic reticulum membrane open
3. Calcium ions diffuse from sarcoplasmic reticulum into the myofibril
4. (By binding to troponin), Ca2+ cause the tropomyosin to move, exposing myosin binding sites on the actin
5. Myosin heads bind actin forming actinomyosin bridges
6. Calcium ions also activate ATP hydrolase
7. Energy from hydrolysis of ATP causes the myosin heads to bend and pull the actin
8. Attachment of ATP to the myosin heads causes the actinmyosin bridges to break so the myosin detaches from actin
9. Myosin heads move back to their original position and reattach at binding sites further along actin
10. Energy from hydrolysis of ATP is also used for active transport of calcium ions into the sarcoplasmic reticulum

Question 6

What does antagonistic mean?

Answer 6

when one muscle contracts the other of the pair relaxes

Question 7

Describe the structure of skeletal muscle

Answer 7

• Muscle fiber bundle
• Motor neurone
• muscle fiber (muscle cell)
• nuclei
• mitochondrion
• myofibril
• Z-line
• Actin and Myosin

Question 8

Describe the structure of a muscle fiber

Answer 8

• sarcoplasmic reticulum
• T-tubule
• Thick filament- myosin
• thin filament- actin
• myofibril
• sarcolemma
• mitochondrion
• sarcomere

Question 9

Describe the structure of a sarcomere

Answer 9

• Z-line
• M-line
• myosin and actin
• H zone
• I band
• A band