3.6.3 Skeletal muscles as Effectors (C15)

Question 1

Describe the role of ATP in muscle contraction

Answer 1

5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites);

Question 2

Describe the role of Ca ions in muscle contraction

Answer 2

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;

Question 3

role of glycogen in skeletal muscle?

Answer 3

1. As a store of glucose
   OR
   To be hydrolysed to glucose;
2. For respiration/to provide ATP;

Question 4

Describe the sliding filament theory of muscle contraction

Answer 4

1. Calcium ions diffuse into myofibrils from the sarcoplasmic reticulum
2. Ca2+ binds to tropomyosin changing its shape and move
3. This change exposes the myosin binding sites on the actin
4. Myosin ‘heads’ bind to the Actin forming a cross bridge.
5. Ca2+ activates ATPase hydrolysing ATP. Myosin ‘heads’ tilt in a rowing motion pulling actin molecules.
6. ATP can now bind to the Myosin head, changing the shape and breaking the cross bridge
7. ATP is hydrolysed by the head providing energy for the head to flip back/re-cock
8. ADP and Pi remains on the head

Question 5

Label the parts of the neuromuscular junction

Answer 5

Question 6

What is the role of T tubules

Answer 6

They are invaginations in the sarcolemma, they transmit depolarisation to the sarcoplasmic reticulum

Question 7

What is the role of the sarcoplasmic reticulum?

Answer 7

It is depolarised and releases Ca2+ ions that diffuse into the myofibrils to stimulate muscle contraction

Question 8

What are the missing labels?

Answer 8

Question 9

Which band stays the same when the sarcomere contracts

Answer 9

A band

Question 10

Which bands become shorter when the muscle contracts

Answer 10

H zone and I band

Question 11

In general how to muscles contract?

Answer 11

1. When a muscle contracts, the sarcomere shortens, and the Z lines are pulled closer together
2. This happens because actin filaments slide between myosin filaments
3. During contraction, the I band, sarcomere and the H zone decrease in length
4. The A band remains the same

Question 12

What is the role of phosphocreatine in muscles?

Answer 12

Phosphocreatine is stored in muscle
When contraction demands are too high, respiration cannot meet the demands for ATP

Phosphocreatine is stored in the muscle and is a source of phosphate
The phosphate is used to generate ATP immediately

(but it will run out!) Phosphocreatine needs to be regenerated when muscles relax

Question 13

Describe a fast twitch muscle fibre

Answer 13

• More powerful contractions
• Only for a short time
• Thicker filaments
• More filaments
• Stores of glycogen
• Anaerobic respiration
• Store of phosphocreatine

Question 14

Describe a slow twitch muscle fibre

Answer 14

• Less powerful contractions over a longer period of time
• Aerobic respiration
• Stores of myoglobin (stores oxygen)
• Rich blood supply
• Many mitochondria

Question 15

Compare and contrast the NMJ and the synapse

Answer 15

• Synapse connects neurone to neurone whereas NMJ connects neurone to muscle
• Both have Ach as a neurotransmitter
• Ach binds to specific receptors in both the muscle and postsynapsynaptic membrane
• Both are unidirectional
• Both lead to depalarisation using Na+ ions
• Both require Ca2+ ions
• Ca2+ ions requires in the muscle to initiate contraction, Ca2+ ions are not required for action potential propagation