What happens during a contraction — practice questions

Question 1 · difficulty L1 · recall

During contraction the H zone generally:

• A. narrows or may disappear
• B. widens
• C. becomes a Z line
• D. remains always unchanged

Question 2 · difficulty L1 · recall

During contraction the I band generally:

• A. shortens
• B. becomes the A band
• C. remains exactly unchanged
• D. lengthens

Question 3 · difficulty L1 · recall

During contraction the length of the A band:

• A. doubles
• B. disappears
• C. remains essentially constant
• D. shortens to zero

Question 4 · difficulty L1 · recall

The ion that binds troponin to initiate skeletal-muscle contraction:

• A. chloride
• B. iron
• C. sodium
• D. calcium

Question 5 · difficulty L1 · recall

According to the sliding filament theory, what happens to actin and myosin filaments during contraction?

• A. Both filaments become much shorter
• B. They slide past one another without substantially changing their own lengths
• C. Only myosin filaments disappear
• D. Actin is converted into myosin

Question 6 · difficulty L2 · understanding

What is the immediate role of calcium ions in initiating skeletal muscle contraction?

• A. They replace ATP on the myosin head
• B. They break down actin filaments
• C. They bind to troponin and shift tropomyosin away from actin's myosin-binding sites
• D. They directly shorten the Z lines

Question 7 · difficulty L2 · understanding

What happens when ATP binds to a myosin head that is attached to actin?

• A. Actin is hydrolysed
• B. The Z lines move farther apart permanently
• C. Calcium is released from troponin
• D. The myosin head detaches from actin

Question 8 · difficulty L3 · application

During contraction, which sarcomere change is expected?

• A. The I band and H zone become narrower while the A band remains constant
• B. The A band shortens while the I band remains constant
• C. All bands lengthen equally
• D. The Z lines move farther apart

Question 9 · difficulty L3 · application

A muscle fibre is stimulated but calcium cannot be released into the sarcoplasm. Which event is most directly blocked?

• A. ATP production by mitochondria
• B. Exposure of myosin-binding sites on actin
• C. Formation of thick myosin filaments
• D. Generation of the action potential in the motor neuron

Question 10 · difficulty L3 · understanding

Choose the correct statements regarding muscle contraction. A. A motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre. B. The neural signal generates an action potential which causes the release of $\mathrm{Ca}^{++}$into sarcoplasm. C. Increase in $\mathrm{Ca}^{++}$inactivates the actin for breaking cross bridges. D. Actin binds to the myosin head to form a cross bridge. E. Shortening of sarcomere takes place, by pulling actin filaments towards the centre of ' A ' band. Choose the correct answer from the options given below :

• A. C and D only
• B. A and B only
• C. C and E only
• D. A, B, D and E only