Dr Gawad Physiology Course Online Exam - CVS – Course Lecture 1- Introduction, Rhythmicity
11 MCQs (Only one correct answer)
Each MCQ: 1 mark, Total mark: 11
Allowed time: 10 minGood Luckdr Mohammed Abel Gawad
- 1.
The cardiac muscle fibres :
- A.
Are unstriated muscle fibres.
- B.
Form true syncytiutn.
- C.
Are poor in mitochondria.
- D.
Have low resistance bridges and tight gap junctions.
Correct Answer
B. Form true syncytiutn.Explanation
Cardiac muscle fibers form true syncytium. A syncytium is a type of tissue where individual cells are fused together, allowing electrical signals to pass freely between cells. In the case of cardiac muscle, this syncytium allows for coordinated contraction of the entire heart, ensuring efficient pumping of blood. This characteristic is essential for the proper functioning of the heart and distinguishes cardiac muscle from other muscle types.Rate this question:
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- 2.
About the pacemaker potential, all the following is true except:
- A.
Its amplitude is -80 to -90 mV.
- B.
It is unstable during rest.
- C.
Its slope is decreased by increased permeability to K.
- D.
The firing level occurs at a potential difference of about -45 mV.
Correct Answer
A. Its amplitude is -80 to -90 mV.Explanation
The pacemaker potential refers to the gradual depolarization of the membrane potential in certain cells, such as cardiac cells, that spontaneously generate action potentials. The amplitude of the pacemaker potential is not fixed and can vary depending on various factors. Therefore, it is incorrect to state that its amplitude is -80 to -90 mV.Rate this question:
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- 3.
S.A.N. is the normal pacemaker because:
- A.
The fastest impulse discharge.
- B.
Location in the atrium.
- C.
Neural control.
- D.
Relative position to the A.V.N.
Correct Answer
A. The fastest impulse discharge.Explanation
The correct answer is "The fastest impulse discharge." This is because the S.A.N. (sinoatrial node) is responsible for initiating the electrical impulses that regulate the heart's rhythm. It is known as the "natural pacemaker" because it generates these impulses at the fastest rate compared to other nodes in the heart.Rate this question:
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- 4.
The pacemaker potential un-stability is due primarily to:
- A.
Slow decrease in K+ permeability
- B.
Slow increase in K permeability.
- C.
Hyperpolarization stimulating voltage gated Na channels.
- D.
Rapid increase in Ca permeability.
Correct Answer
C. Hyperpolarization stimulating voltage gated Na channels.Explanation
The pacemaker potential refers to the spontaneous depolarization of certain cells, such as those in the sinoatrial node of the heart, which sets the rhythm for the entire organ. This depolarization is primarily caused by the slow increase in potassium (K+) permeability, which allows K+ ions to leave the cell, leading to hyperpolarization. This hyperpolarization then stimulates voltage-gated sodium (Na+) channels to open, allowing Na+ ions to enter the cell and depolarize it. Therefore, the correct answer is hyperpolarization stimulating voltage-gated Na+ channels.Rate this question:
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- 5.
The steepest prepotenial normally occurs in the:
- A.
Atrioventricular node (AVN).
- B.
Bundle of His.
- C.
Purkinje fibres.
- D.
Sinoatrial node (SAN).
- E.
Ventricular muscle cells.
Correct Answer
D. Sinoatrial node (SAN).Explanation
The sinoatrial node (SAN) is responsible for initiating the electrical impulses that regulate the heart's rhythm. It acts as the natural pacemaker of the heart. The SAN generates electrical signals that travel through the atria, causing them to contract and pump blood into the ventricles. The impulses then pass through the atrioventricular node (AVN), Bundle of His, and Purkinje fibers, finally reaching the ventricular muscle cells. However, the SAN has the steepest prepotential, meaning it has the fastest rate of spontaneous depolarization, which allows it to set the pace for the rest of the heart.Rate this question:
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- 6.
Intrinsic heart rate refers to:
- A.
Heart rate that is produced by AVN
- B.
Heart rate that is produced due to the permeability of SAN to Na
- C.
Heart rate that is produced by atrial muscles
- D.
None of the above
Correct Answer
B. Heart rate that is produced due to the permeability of SAN to NaExplanation
Intrinsic heart rate refers to the heart rate that is produced due to the permeability of the sinoatrial node (SAN) to sodium (Na). The SAN is responsible for initiating the electrical signals that regulate the heart's rhythm, and its permeability to sodium ions plays a crucial role in determining the heart rate. Therefore, the correct answer is "heart rate that is produced due to the permeability of SAN to Na."Rate this question:
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- 7.
The main cause of plateau in cardiac muscle action potential:
- A.
Out flux of K in exchange of Na
- B.
Outflux of K
- C.
Influx of Ca in exchange to efflux of Na
- D.
The balance in influx of and out flux of positive ions along the membrane
Correct Answer
D. The balance in influx of and out flux of positive ions along the membraneExplanation
The main cause of plateau in cardiac muscle action potential is the balance in influx of and outflux of positive ions along the membrane. This balance helps maintain the prolonged depolarization phase characteristic of the plateau, which allows for sustained contraction of the cardiac muscle. The influx of calcium in exchange for efflux of sodium also contributes to the plateau phase, but the overall balance of positive ions is the primary cause.Rate this question:
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- 8.
Which of the following is considered as an ectopic pacemaker:
- A.
SAN
- B.
AVN
- C.
Bundle of His
- D.
Ventricular muscle
Correct Answer
B. AVNExplanation
The AVN (atrioventricular node) is considered as an ectopic pacemaker. The AVN is a group of cells located between the atria and ventricles in the heart. It normally receives electrical impulses from the sinoatrial node (SAN) and conducts them to the ventricles, causing them to contract. However, in certain cases, the AVN can become the primary pacemaker and initiate the electrical impulses, leading to abnormal heart rhythms. This makes the AVN an ectopic pacemaker, as it is taking over the role of the SAN in initiating the heartbeat.Rate this question:
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- 9.
Regarding the differences between cardiac muscle and pace maker action potentials, which of the following is true:
- A.
Cardiac muscle action potential has lower magnitude than pacemaker
- B.
Both have fast depolarization
- C.
Both have 2 parts repolarization
- D.
Pacemaker action potential is unstable while cardiac muscle potential is not.
Correct Answer
D. Pacemaker action potential is unstable while cardiac muscle potential is not.Explanation
The correct answer is that pacemaker action potential is unstable while cardiac muscle potential is not. This is because pacemaker action potentials have an unstable resting membrane potential, meaning they can spontaneously depolarize without external stimuli. In contrast, cardiac muscle action potentials have a stable resting membrane potential and require external stimuli, such as electrical signals from the pacemaker cells, to initiate depolarization.Rate this question:
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- 10.
Regarding pacemaker action potential which is true:
- A.
Ca is not important for its maintenance
- B.
Na is important to initiate it, but not important for its maintenance
- C.
Repolarization is due to out flux of K in exchange of Na
- D.
None of the above
Correct Answer
B. Na is important to initiate it, but not important for its maintenanceExplanation
In the pacemaker action potential, Na (sodium) is important for its initiation as it causes depolarization of the membrane. However, once the action potential is initiated, the maintenance of the action potential does not depend on Na. Instead, repolarization occurs due to the outflux of K (potassium) in exchange for Na. Therefore, the correct statement is that Na is important to initiate the pacemaker action potential, but not important for its maintenance.Rate this question:
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- 11.
Regarding the cardiac muscle action potential, which of the following is not true:
- A.
The initial repolarization is due to K efflux
- B.
The plateau is due to balance between the Ca, K mobility
- C.
The complete repolariztion is at the end of phase 3 when all K is effluxed
- D.
Na is an important ion for depolarization
- E.
None of the above
Correct Answer
C. The complete repolariztion is at the end of pHase 3 when all K is effluxedExplanation
The complete repolarization is not at the end of phase 3 when all K is effluxed. The repolarization process in cardiac muscle action potential occurs in phase 3, but it is not solely dependent on the efflux of K ions. While the efflux of K ions does contribute to repolarization, other factors such as the closure of Ca channels and the opening of voltage-gated K channels also play a role in restoring the resting membrane potential. Therefore, it is not accurate to say that complete repolarization occurs only when all K ions are effluxed.Rate this question:
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Mar 21, 2023Quiz Edited by
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Mar 12, 2018Quiz Created by
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