Muscle

Question 1

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 1

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 2

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

Answer 2

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

Question 3

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

Answer 3

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

This relates to the sliding filament theory of skeletal muscle contraction

Question 4

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

Answer 4

The speed of the myosin ATPase

Question 5

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

Answer 5

During sliding the A band shortens.

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 6

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

Answer 6

The actin filament moves along the fixed myosin filament

Question 7

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

Answer 7

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

Question 8

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

Answer 8

Ca2+

Ca2+ binds to troponin removing the tropomyosin inhibition.

Question 9

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 9

Actin and Myosin

These are the two main contractile proteins which are responsible for the cross bridge cycle and muscle contraction.

Question 10

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 10

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 11

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

Answer 11

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

this is not a feature of smooth muscle contraction. There is no troponin in smooth muscle. This is a feature of striated muscle contraction.

Question 12

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

Answer 12

The sarcoplasmic reticulum is responsible for Ca2+ uptake.

The sarcoplasmic reticulum releases Ca2+ .

Question 13

Despite the fact that the same amount of activating [Ca2+]inside 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 13

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 14

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

Answer 14

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

Question 15

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

Answer 15

A

Question 16

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

Answer 16

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 17

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

Answer 17

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

Question 18

Cardiac and smooth muscle differ from skeletal muscle in that:

Answer 18

The individual muscle cells are electrically coupled.

Their control of contraction is myogenic.

Question 19

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

Answer 19

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

The sarcoplasmic reticulum in cardiac myocytes is less extensive than that of skeletal muscle.

Question 20

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 20

Titin, tendons and Alpha-actinin.

These are in parallel and in series elastic protein components.