Muscle MCQ Flashcards
The major difference between ion channels and ion pumps is
A their dependence on adenosine trisphosphate (ATP)
B the species of ions that they move
C their locations on the cell membrane
D their specificity for moving particular ions
E their molecular weights
A
Which of the following BEST describes the period of time between the peak of an action potential and the peak of the cytoplasmic Ca2+ transient during excitation-contraction coupling in mammalian skeletal muscle (at normal body temperature)?
A 2 s
B 0.2 ms
C 20 ms
D 2 ms
E 0.02 ms
C (?)
A potential five-fold increase in cardiac output in a person going from a resting state to one of intense exercise suggests that
A resistance in the arteries has increased
B both the stroke volume and pacing rate of the heart must have increased
C the diastolic phase of the cardiac cycle has increased
D the rate of Na+ (sodium) channel inactivation per heart beat in the ventricular myocytes has changed
E the systolic phase of the cardiac cycle has increased
B
At high heart rates (e.g. 150 bpm), the ventricles still fill with blood, because
A of the long relative refractory period
B blood bypasses the atria
C reflexes control ventricular filling
D filling is accomplished in early diastole
E the atria contract with greater force
D
Which of the following is NOT an effect of the parasympathetic nervous system on the heart?
A increased inward Ca2+ current
B slowed pacemaker activity
C slowed closure of K+ channels
D weakened atrial contraction
E decreased inward Ca2+ current
A
What is the major difference between skeletal and cardiac type excitation-contraction coupling?
A Ca2+ and Na+ action potentials
B different loads of Ca2+ inside the sarcoplasmic reticulum
C a physical coupling of the voltage sensor and Ca2+ release channel in skeletal muscle, and a chemical coupling in cardiac muscle
D the volume of mitochondria in skeletal muscle is much higher than in cardiac muscle, to cope with the relatively higher energy demand
E the rate of action potential propagation between the respective cells, to allow for faster contraction in skeletal muscle compared with cardiac muscle
C
During tetani in skeletal muscle
A there is a fusion of the cytoplasmic Ca2+ transient and force responses that may be complete or incomplete
B there is a fusion of action potentials only
C there is a fusion of the cytoplasmic Ca2+ transient but not force responses
D action potentials regenerate through the T-system via the sarcolemma (surface membrane) to allow fusion of force responses
E there is a fusion of action potentials causing the fusion of force responses
A
Water from a common domestic household source provide a more appropriate medium for the continued beating of an isolated toad heart than double-distilled water from a laboratory, because
A there are more ions in the double-distilled water than the common household water
B the double-distilled water may not have been prepared from the pond where the toad was previously living
C common tap water contains ions such as Ca2+ that are necessary components of the bathing solution of the heart for its normal function
D the heart will more likely generate arrhythmias in the double distilled water than in the common household water
E double-distilled water contains more Ca2+ than common household water
C
The inactivation of the voltage-gated sodium channel in the ventricular cardiomyocyte is
A an event that causes the membrane potential to immediately return to polarised potentials
B an event that takes about 200 milliseconds to occur
C dependent on the opening of potassium channels
D a timed event, occurring very rapidly after activation of the channel
E an event that causes the membrane potential to remain depolarised for about 200 milliseconds
D
The main role of the sarcoplasmic reticulum in striated muscle is to
A generate the force response inside the cell
B hold all of the intracellular potassium ions
C provide magnesium binding sites in the cytoplasm
D to regulate the action potential frequency
E release and resequester calcium ions
E
Cardiac muscle has special structures to ensure electrical and mechanical coupling. These are the
A myobrils and sarcoplasmic reticulum
B desmosomes and gap junctions
C plasma membrane and mitochondria
D gap junctions and Na+ channels
E Na+ channels and desmosomes
B
The transverse (t-) tubule system of skeletal muscle is an important structure that
A allows action potentials to be brief in skeletal muscle
B allows action potentials to propagate rapidly into all areas of the fibre
C allows the fibre to be highly elongated
D is an important source of Ca2+ ions
E allows a high frequency of action potentials to excite the muscle
B
If the voltage sensor of the skeletal muscle tubular (t-) system failed to move from its activated state to its inactivated state,
A the muscle would remain refractory to action potentials
B it would activate a damaging contracture
C the muscle would depolarise
D calcium ion release through the ryanodine receptor would be prolonged
E it would cause an arrhythmia
D
What does a voltage-gated Na+ channel require to move from its inactivated state to a reprimed state?
A Ca2+ channels to open
B repolarisation of the membrane
C another action potential to excite the cell
D the Na+ gradient across the membrane to change
E phosphorylation of the channel
B
The electrical events of the atria and ventricles are isolated from each other
A so that the ventricles do not excite the atria
B to prevent the back-flow of blood between the chambers
C so that the left and right side of the heart have the same cardiac output
D so that atrial contraction can finish before ventricular contraction begins
E so that the ventricular contraction terminates during the refractory period of the Na+ channel
D
What will happen if the parasympathetic nervous system secretes acetylcholine onto the sinoatrial node of the heart?
A The Na+ channels inactivate
B There will be an increase in K+ permeability across the plasma membrane of the sinoatrial node
C The action potential frequency will increase
D Blood will stop flowing through the chambers of the heart
E The funny current begins moving ions in the opposite direction
B
An important role of the Na+ -Ca2+ exchanger in cardiomyocytes is to
A allow influx of K+ ions during the diastolic phase
B directly move Ca2+ ions into the sarcoplasmic reticulum
C translocate Ca2+ ions from the cytoplasm to outside the cell in the diastolic phase
D repolarise the cell
E activate release of Ca2+ ions through the ryanodine receptor
C
A rapidly rising Ca2+ transient in a cell would
A lead to cellular death
B cause the sarcoplasmic reticulum to fully deplete of Ca2+ ions
C allow Na+ channels to remain open
D rapidly initiate a cellular response
E saturate all of the cellular Ca2+ buffers
D
The long plateau phase of the action potential in cardiac ventricular myocytes is mainly due to
A delay in the atrioventricular (AV) node
B spontaneous depolarisation of the sinoatrial (SA) node
C repolarisation by Cl- channels
D long inactivation of Na+ channels
E slow Ca2+ influx
E
Which of the following is CORRECT for pacemaker action potentials?
A They depend on Na+ channels for the fast depolarisation phase
B At threshold, Ca2+ influx occurs
C They have a slow outward Na+ current
D They exhibit stable resting membrane potentials
E Their rate cannot change
B
At the time of the QRS complex,
A the atria contract
B ventricular pressure exceeds atrial pressure
C the ventricular wall repolarises
D aortic pressure initially increases
E venous return is filling the ventricle
B
What would happen if the skeletal muscle voltage sensor failed to change from its activated state to its inactivated state following membrane depolarisation?
A The Ca2+ release channel would not activate
B Released Ca2+ will not be enough to activate force production
C Ca2+ release from sarcoplasmic reticulum would be prolonged
D There would be no Ca2+ release
E The surface membrane would not repolarise
C
Which of the following events occurs during systole?
A Blood moves from the atria to the ventricle
B The pressure in the left ventricle exceeds that of the aorta
C There is depolarisation of the atria
D There is a delay of the action potential at the atrioventricular (AV) node
E Ca2+ concentration is low in the cytoplasm of the ventricular myocytes
B
An ion channel is able to
A translocate from one membrane to another in response to a change in membrane voltage
B change its conformation in response to a change in membrane voltage
C begin passing ions without changing its conformation
D move between the states of inactivation and reprimed without a change in membrane voltage E remain open all the time
B
Summation in cardiac muscle is prevented mainly due to
A spontaneous depolarisation of the sinoatrial (SA) node
B slow Ca2+ influx
C long inactivation of Na+ channels
D delay in the atrioventricular (AV) node
E long relative refractory period
B
The structure of skeletal muscle fibres shows
A a t-tubule at every second sarcomere
B a t-tubule at every sarcomere t-tubules at every sarcomere
C four t-tubules at every sarcomere
D no t-tubules
E six t-tubules at every sarcomere
B
An isolated frog heart will continue to beat for longer in London tap water compared to distilled water, because
A frogs contain London tap water
B London tap water contains calcium that is essential for cardiac contraction
C London tap water contains chloride that is essential for cardiac contraction
D London tap water is like the water in the frog’s pond
E frog hearts are not very fussy about the cleanliness of water
B
Which of the following statements is INCORRECT? At the time of the QRS complex
A venous return is filling the ventricle
B aortic pressure initially declines
C the atria relax
D ventricular pressure exceeds atrial pressure
E the ventricular wall depolarizes
A
Which of the following is the major difference between excitation-contraction coupling
ong in skeletal and cardiac muscle?
A rate of rise of the cytoplasmic Ca2+ transient
B activation of the ryanodine receptor by mechanical coupling in skeletal muscle and Ca2+ - induced Ca2+ release in cardiac muscle
C activation of the contractile apparatus
D the respective ultrastructure of the membranes in skeletal and cardiac muscle
E the role of Na+ channels
B
What do cardiomyocyte and nerve fibre action potentials have in common?
A They cannot excite adjacent cells
B They are activated by a Na+ current and repolarised by a K+ current
C They act like internal pacemakers
D They have a similar reliance on the activation of calcium channels
E They have a very similar duration
B
A tetanic contraction in skeletal muscle is possible because [1.5 marks]
A Na+ channels never inactivate in skeletal muscle
B there is a relatively high abundance of Ca2+ stored in the sarcoplasmic reticulum of
skeletal muscle compared to cardiac muscle
C the skeletal muscle has an elastic element in its contractile proteins that is not present in
the cardiac muscle
D the duration of the action potentials that excite the tissue are less than 2 ms in duration
E there is a greater density of ryanodine receptors in skeletal muscle than cardiac muscle
D
Two important roles of the L-type Ca2+ channel Ca2+ conductance in cardiomyocytes are
[1.5 marks]
A to increase the Ca2+ content of the cell and to force it to relax
B to repolarise the sino-atrial node and start the rising phase of the unstable baseline of the
sino-atrial node action potential
C to directly trigger contraction and relaxation when the pacing rate of the heart increases
D to maintain depolarization of the t-system membrane and to provide Ca2+ entry to the
cytoplasm for activation of the ryanodine receptor
E to inactivate the Na+ channel and to repolarize the cell
D
An important role of the Na+-Ca2+ exchanger in cardiomyocytes is to [1.5 marks]
A repolarise the cell
B shorten the diastolic phase
C activate release of Ca2+ through the ryanodine receptor
D directly move Ca2+ into the sarcoplasmic reticulum
E translocate Ca2+ from the cytoplasm to outside the cell in the diastolic phase
E
