3.6.3 Skeletal muscles as Effectors (Unit 6 Responding to Environment)

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

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

Compare and contrast the NMJ and the synapse

Answer 8

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
Any more?

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

When a muscle contracts, the sarcomere shortens, and the Z lines are pulled closer together
This happens because actin filaments slide between myosin filaments
During contraction, the I band, sarcomere and the H zone decrease in length
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