Muscle Online Feedback Quiz 2011 -
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Department of Physiology
Muscle Online Feedback Quiz 2011
Total score: 20 out of 20, 100%
Thank you for completing the Muscle online feedback quiz.
Please review your feedback and revise any areas of weakness.
Once you have finished reading your feedback, scroll to the bottom of this page
and click on the word 'link'. This will take you to your blackboard home page. You
can then access the Physiology 1A page and take the assessment again if you
wish.
1)
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?
The amplitude of the action potentials coming from the motor neuron are larger
during a tetanus.
Because the CaATPase pumps on the sarcoplasmic reticulum work faster
during a single twitch, lowering the [Ca2+] in more quickly, than in the case of the
larger tetanus.
Because the myosin heads, the molecular motor, move more slowly during a
twitch.
The rate of diffusion of Ca 2+ molecules from the sarcoplasmic reticulum to the
contractile proteins is slower during a single twitch.
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.
1 out of 1
This is correct. The answer explains itself. See slide 14 from the skeletal
muscle lecture.
2)
Which ONE of the following statements about smooth muscle is CORRECT?
Calcium-dependent phosphorylation of myosin regulatory light chains is
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responsible for the contraction of smooth muscle.
Actin and myosin filaments are organized in sarcomeres as seen in cardiac and
skeletal muscle.
Smooth muscle can only be stimulated to contract by the CNS.
Smooth muscle is one of the three striated muscle types found in the body.
In smooth muscle, actin filaments and associated myosin attach to regular Z
lines.
1 out of 1
This statement is correct.
3)
Which ONE of the following bands does not change in length when a skeletal
muscle fibre contracts isotonically?
D
M
A
I
H
1 out of 1
This is correct. The A band stays the same length.
4)
What are the two major factors which make a muscle fibre “fast-twitch” or “slowtwitch”?
The amount of glycogen and ATP present in a fibre.
The density of calcium channels present in the sarcolemma and the
arrangement of the t-tubular system with respect to the individual fibrils in a fibre.
The density of mitochondria and the elasticity of the muscle protein “titin”.
The rate at which myosin can hydrolyse ATP and the arrangement of the internal
calcium store (Sarcoplasmic Reticulum) with respect to individual fibrils in a fibre.
The type of actin and myosin expressed by a fibre.
1 out of 1
This is correct.
5)
Which ONE of the following statements regarding the sliding filament theory of
muscle contraction is CORRECT?
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The cross-bridges are activated once during a contraction.
The cross-bridges have an unlimited range of movement.
Sliding is caused by the cross-bridges on the myosin molecule interacting with
specific sites on the actin molecule.
Every cycle four molecules of ATP are used by each myosin head.
Every cycle two molecules of ATP are used by each myosin head.
1 out of 1
This is correct.
6)
In general human muscles are made up of 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.
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% fastfibre profile and marathon runners having a higher than 50% slow-fibre profile.
No, there is little individual variation in fibre type proportions.
No, it is the high density of mitochondria present in both power and endurance
athletes which determines their elite performance characteristics.
Yes, in fact these elite athletes were born with muscles which are all fast-fibres,
such as high jumpers, or all slow fibres, such as marathon runners.
The question cannot be answered because currently exercise scientists cannot
measure the fibre type ratios in living athletes.
1 out of 1
This is correct, see slide 18 from your skeletal muscle lecture.
7)
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
these elastic components?
Sarcolemma, t-tubules, sarcoplasmic reticulum.
Dystrophin, Desmin, αβ-Crystalin.
Epimysium, Perimysium, Endomysium.
Troponin and tropomyosin.
Actin and Myosin.
1 out of 1
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This is correct. These are in parallel elastic connective tissue
components.
8)
Which ONE of the following is NOT part of the sequence of skeletal muscle
contraction?
An action potential in the surface membrane.
The sarcoplasmic reticulum (SR) is responsible for calcium uptake.
An action potential conducted down the t-tubules.
E-C coupling.
Increase in the myoplasmic concentration of calcium.
1 out of 1
This is the incorrect statement. The sarcoplasmic reticulum releases
calcium.
9)
Which ONE of the following is NOT a feature of smooth muscle contraction?
Smooth muscle myosin is a type II myosin, consisting of two heavy chains and
two pairs of light chains. The myosin molecule is folded when dephosphorylated.
When type II myosin phosphorylates, it unfolds and assembles into filaments, the
actin binding site on the myosin head is exposed, and myosin can then bind to actin
filaments to cause cell contraction.
An increase in cytosolic calcium induces calmodulin binding to myosin-light
chain kinase.
Phosphorylation of the myosin light chain converts myosin into its active form
which can then bind to f-actin.
The regulation of the actin-myosin interaction occurs by calcium binding to
troponin.
1 out of 1
This is the incorrect statement - this is not a feature of smooth muscle
contraction.There is no troponin in smooth muscle. This is a feature of
striated muscle contraction.
10 )
If you calculate the time it would take for extracellular Ca 2+ to diffuse to the center
of a skeletal muscle fibre, the fastest predicted rate for onset of contraction would
be 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?
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This is possible because Ca 2+ is released from nuclear stores close to the
contractile proteins.
The concentration difference between intracellular and extracellular Ca 2+ is so
large (1 to 20,000) that the Ca 2+ diffuses much more rapidly than expected.
The concentration difference between intracellular and extracellular Ca 2+ is so
small (approx 1 to 1.5 ) that there is no barrier to Ca 2+ diffusing to the contractile
proteins.
The rate of onset of muscle contraction is dependent on the diffusion of
intracellular ATP and not the diffusion of Ca 2+.
Membrane invaginations (t-tubular system) carry the action potential into the
center of the muscle fibre.
1 out of 1
This statement is correct.
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?
Nebulin and Myosin
Desmin and Nebulin
Myosin and Titin
Actin and Myosin
Actin and a -actinin
1 out of 1
This is correct. These are the two main contractile proteins which are
responsible for the cross bridge cycle and muscle contraction.
12 )
Cardiac and smooth muscle differ from skeletal muscle in that:
The individual muscle cells are electrically coupled.
They contract more quickly.
They DO NOT require an influx of Ca 2+ from the extracellular fluid to initiate
contraction.
They are under voluntary control.
Each individual muscle cell has its own nerve supply.
1 out of 1
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This is correct. Their control of contraction is myogenic.
13 )
Which ONE of the following statements regarding the internal structure of a skeletal
muscle fibre is TRUE?
Absence of desmin results in the skeletal muscle disease Duchenne Muscular
Dystrophy.
The main elastic (spring) component is the endomysium.
The (myo) fibrils are surrounded by the skeletal muscle (myo) nuclei.
Each adult muscle fibre contains around 20 (myo) fibrils.
Each sarcomere has two t-tubules located at the junctions of the A/I band.
1 out of 1
This statement is true.
14 )
Which ONE of the following is NOT a difference in the cytomembrane of cardiac vs
skeletal muscle?
The sarcoplasmic reticulum of cardiac muscle is more extensive than that of
skeletal muscle.
Diads are typical in cardiocytes ,while triads are typical in skeletal muscle.
T tubules are found at the level of the Z disk in cardiac muscle, and are
substantially larger than those of skeletal muscle found at the A-I junction.
Mitochondria are more abundant in cardiac muscle than in skeletal muscle and
contain numerous cristae.
The sarcoplasmic reticulum of cardiac muscle is not as extensive as that of
skeletal muscle.
1 out of 1
This answer is correct. The sarcoplasmic reticulum in cardiac myocytes is
less extensive than that of skeletal muscle.
15 )
When you exercise at 75% of maximal intensity over a period of 20 minutes, there
is a reduction in the force produced by your muscles. What is ONE likely cause of
this fatigue?
Potassium ions entering the internal calcium store, the sarcoplasmic reticulum,
and causing a precipitation of calcium.
Phosphate ions from the breakdown of ATP during exercise entering the internal
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calcium store, the sarcoplasmic reticulum and causing a precipitation of calcium.
ATP produced from the mitochondria entering the internal calcium store, the
sarcoplasmic reticulum and causing a precipitation of calcium.
Sodium ions entering the internal calcium store, the sarcoplasmic reticulum, and
causing a precipitation of calcium.
Chloride ions entering the internal calcium store, the sarcoplasmic reticulum,
and causing a precipitation of calcium.
1 out of 1
This is correct. If you block phosphate from entering the sarcoplasmic
reticulum during fatigue, the loss of force is largely prevented.
16 )
Which ONE of the following statements is CORRECT of an isometric tetanic
contraction?
The shortening is isokinetic.
The muscle shortens but does not generate tension.
The muscle shortens under a fixed load.
The set length of the muscle determines the level of tension developed.
The muscle contracts at its maximum velocity of shortening.
1 out of 1
This is correct. This relates to the sliding filament theory of skeletal
muscle contraction.
17 )
What determines whether a skeletal muscle fibre is fast or slow?
The elasticity of the endomysium.
The organization of the nuclei in relation to the myofibrils.
The different numbers of t-tubules present per sarcomere.
The speed of the myosin ATPase.
The number of mitochondria within the fibre.
1 out of 1
This is correct.
18 )
When skeletal muscle shortens, the I band contracts while the A band does not
change in length. The explanation for this is:
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The actin and myosin filaments are both moving.
The titin molecule pulls the actin filaments towards the Z-line.
The thick myosin filament moves over the thin actin filament.
Dystrophin pulls the myosin filament towards the Z-line.
The actin filament moves along the fixed myosin filament.
1 out of 1
This is correct.
19 )
An increase in the intracellular concentration of which ion/s is/are responsible for
initiating muscle contraction?
Na + & Ca 2+
Na +
Ca 2+ & K+
K+
Ca 2+
1 out of 1
This is correct. Calcium binds to troponin removing the tropomyosin
inhibition.
20 )
Which ONE of the following statements regarding the sliding filament theory of
muscle contraction is FALSE?
The cross-bridges have a limited range of movement.
Sliding is caused by the cross-bridges interacting with specific sites on the actin
molecule.
Muscle works by the relative sliding of the thin filament (actin) over the thick
filament (myosin).
During sliding the A band shortens.
Each individual cross bridge is activated cyclically.
1 out of 1
This is the false statement. The A band corresponding to the position of
myosin at the center of the sarcomere is the only band not to change in
length during contraction.
Link...
Copyright (c) Department of Physiology, University of New South Wales, Sydney, Australia 2010
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Should you encounter a problem please notify:L.Ulman@unsw.edu.au
Perception is licensed to The University of New South Wales
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