Muscle

Question 1

Which ONE of the following statements regarding the internal structure of a skeletal muscle fibre is TRUE?

Answer 1

Each sarcomere has two t-tubules located at the junctions of the A/I band.

Question 2

Which ONE of the following is NOT a difference in the cytomembrane of cardiac vs skeletal muscle?

Answer 2

The sarcoplasmic reticulum of cardiac muscle is more extensive than that of skeletal muscle.

Question 3

Cardiac and smooth muscle differ from skeletal muscle in that:

Answer 3

The individual muscle cells are electrically coupled.

Question 4

When skeletal muscle shortens, the I band contracts while the A band does not change in length. The explanation for this is:

Answer 4

The actin filament moves along the fixed myosin filament.

Question 5

An increase in the intracellular concentration of which ion/s is/are responsible for initiating muscle contraction?

Answer 5

Ca2+

Question 6

What determines whether a skeletal muscle fibre is fast or slow?

Answer 6

The speed of the myosin ATPase

Question 7

If you calculate the time it would take for extracellular Ca2+ to diffuse to the middle of a skeletal muscle fibre, the fastest predicted rate for onset of contraction would be in the order of 100 msec after the arrival of the motor neuron action potential. Why then is it possible for a muscle fibre to start contracting only 10 msec after the arrival of the motor nerve action potential?

Answer 7

Membrane invaginations (t-tubular system) carry the action potential into the middle of the muscle fibre triggering a global release of Ca2+ from the intracellular Ca2+ store.

Question 8

Which ONE of the following is NOT a feature of smooth muscle contraction?

Answer 8

The regulation of the actin-myosin interaction occurs by calcium binding to troponin.

Question 9

Despite the fact that the same amount of activating [Ca2+]in is released in each case, the size of a single skeletal muscle twitch is about 4 times smaller than a fused tetanus. Why is this?

Answer 9

Because in a twitch (which occurs when muscle is activated by a single action potential) there is not enough time to take up all the elastic tension before the muscle starts to relax again.

Question 10

Which ONE of the following is NOT part of the sequence of skeletal muscle contraction?

Answer 10

The sarcoplasmic reticulum is responsible for Ca2+ uptake.

Question 11

During an isotonic contraction in skeletal muscle the I band shortens while the A band does not change in length. What are the proteins which comprise the I band and A band?

Answer 11

Actin and Myosin

Question 12

Which ONE of the following statements regarding the sliding filament theory of muscle contraction is FALSE?

Answer 12

During sliding the A band shortens.

-This is the false statement. The A band corresponding to the position of myosin at the centre of the sarcomere is the only band not to change in length during contraction.

Question 13

Which ONE of the following statements is CORRECT of an isometric tetanic contraction?

Answer 13

The set length of the muscle determines the level of tension developed.

Question 14

Skeletal muscle can be modeled as contractile proteins connected to the skeleton by in series and in parallel elastic components. Which of the following make up the protein component of the elastic capability of skeletal muscle?

Answer 14

Titin, tendons and Alpha-actinin.

Question 15

Which ONE of the following bands does not change in length when a skeletal muscle fibre contracts isotonically?

Answer 15

A

-The A band stays the same length.

Question 16

Which ONE of the following statements about smooth muscle is CORRECT?

Answer 16

Calcium-dependent phosphorylation of myosin regulatory light chains is responsible for the contraction of smooth muscle.

Question 17

In general, human muscles are made up of approximately a 50:50 mixture of fast and slow fibres. Can the exceptional abilities of elite high jumpers (power athletes) and marathon runners be explained by having predominantly fast or slow muscle fibre types in key muscles? Choose the statement which gives the MOST WIDELY accepted explanation.

Answer 17

Yes, at elite levels like the Olympics, it appears that power and endurance athletes are born and not made, with high jumpers having a higher than 50% fast-fibre profile and marathon runners having a higher than 50% slow-fibre profile.

Question 18

The correct nomenclature of the connective tissue sheaths in skeletal muscle is:

Answer 18

**Whole muscle is surrounded by the EPIMYSIUM, fascicles by the PERIMYSIUM and individual fibres by the ENDOMYSIUM.

Question 19

What are the two major factors which make a muscle fibre “fast-twitch” or “slow-twitch”?

Answer 19

The rate at which myosin can hydrolyse ATP and the arrangement of the internal calcium store (Sarcoplasmic Reticulum) with respect to individual (myo) fibrils in a fibre.

Question 20

Which ONE of the following statements regarding the sliding filament theory of muscle contraction is CORRECT?

Answer 20

Sliding is caused by the cross-bridges on the myosin molecule interacting with specific sites on the actin molecule.