Dr Gawad Physiology Course Online Exam - CVS – Course Lecture 1- Introduction, Rhythmicity,

2.

About the pacemaker potential, all the following is true except:

Its amplitude is -80 to -90 mV.
It is unstable during rest.
Its slope is decreased by increased permeability to K.
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 is the gradual depolarization that occurs in certain specialized cells, such as cardiac cells, that have the ability to spontaneously generate action potentials. The amplitude of the pacemaker potential refers to the difference in potential between the resting membrane potential and the peak depolarization. In this case, the correct answer is that the amplitude of the pacemaker potential is not -80 to -90 mV. This is because the pacemaker potential typically has a smaller amplitude, usually around -60 mV.

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3.

S.A.N. is the normal pacemaker because:

The fastest impulse discharge.
Location in the atrium.
Neural control.
Relative position to the A.V.N.

Correct Answer

A. The fastest impulse discharge.

4.

The pacemaker potential un-stability is due primarily to:

Slow decrease in K+ permeability
Slow increase in K permeability.
Hyperpolarization stimulating voltage gated Na channels.
Rapid increase in Ca permeability.

Correct Answer

A. Hyperpolarization stimulating voltage gated Na channels.

Explanation

The pacemaker potential refers to the spontaneous depolarization of certain cells, such as those in the sinoatrial (SA) node of the heart, which ultimately leads to the generation of an action potential. This depolarization is primarily caused by the opening of voltage-gated Na+ channels, which allow Na+ ions to enter the cell and depolarize it. Hyperpolarization, which refers to a more negative membrane potential, can stimulate these voltage-gated Na+ channels to open and contribute to the pacemaker potential's instability. Therefore, the correct answer is hyperpolarization stimulating voltage gated Na channels.

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5.

The steepest prepotenial normally occurs in the:

Atrioventricular node (AVN).
Bundle of His.
Purkinje fibres.
Sinoatrial node (SAN).
Ventricular muscle cells.

Correct Answer

A. 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, setting the pace for the rest of the cardiac conduction system. The SAN has the steepest prepotential, which refers to the rapid depolarization that occurs before each heartbeat. This prepotential is essential for the proper functioning of the heart, as it ensures a coordinated and efficient contraction of the atria before the ventricles contract.

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6.

Intrinsic heart rate refers to:

Heart rate that is produced by AVN
Heart rate that is produced due to the permeability of SAN to Na
Heart rate that is produced by atrial muscles
None of the above

Correct Answer

A. Heart rate that is produced due to the permeability of SAN to Na

Explanation

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 electrical impulses that regulate the heart's rhythm. These impulses are generated by the movement of sodium ions across the cell membrane, which ultimately determines the heart rate. Therefore, the correct answer is "heart rate that is produced due to the permeability of SAN to Na."

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7.

The main cause of plateau in cardiac muscle action potential:

Out flux of K in exchange of Na
Outflux of K
Influx of Ca in exchange to efflux of Na
The balance in influx of and out flux of positive ions along the membrane

Correct Answer

A. The balance in influx of and out flux of positive ions along the membrane

Explanation

The correct answer is the balance in influx of and out flux of positive ions along the membrane. This is because the action potential in cardiac muscle cells is generated by the movement of ions across the cell membrane. The influx of positive ions, such as sodium and calcium, and the efflux of positive ions, such as potassium, are balanced to maintain the electrical equilibrium and allow for the proper contraction and relaxation of the cardiac muscle. Any disruption in this balance can lead to abnormalities in the action potential and potentially cause a plateau phase.

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8.

Which of the following is considered as an ectopic pacemaker:

SAN
AVN
Bundle of His
Ventricular muscle

Correct Answer

A. AVN

Explanation

The AVN (Atrioventricular Node) is considered as an ectopic pacemaker. An ectopic pacemaker is an abnormal site in the heart that generates electrical impulses and takes over the role of the sinoatrial node (SAN) as the primary pacemaker. The AVN is located between the atria and the ventricles and is responsible for delaying the electrical signal before it is transmitted to the ventricles. In certain cases, when the SAN fails to function properly, the AVN can become the dominant pacemaker and initiate the heart's contractions.

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9.

Regarding the differences between cardiac muscle and pace maker action potentials, which of the following is true:

Cardiac muscle action potential has lower magnitude than pacemaker
Both have fast depolarization
Both have 2 parts repolarization
Pacemaker action potential is unstable while cardiac muscle potential is not.

Correct Answer

A. Pacemaker action potential is unstable while cardiac muscle potential is not.

Explanation

The given answer is correct because it accurately states that pacemaker action potential is unstable while cardiac muscle potential is not. Pacemaker cells in the heart have an unstable resting membrane potential, which means that they spontaneously depolarize and initiate action potentials. On the other hand, cardiac muscle cells have a stable resting membrane potential and do not spontaneously depolarize. This key difference in the stability of action potentials between pacemaker cells and cardiac muscle cells is crucial for the coordinated contraction and rhythm of the heart.

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10.

Regarding pacemaker action potential which is true:

Ca is not important for its maintenance
Na is important to initiate it, but not important for its maintenance
Repolarization is due to out flux of K in exchange of Na
None of the above

Correct Answer

A. Na is important to initiate it, but not important for its maintenance

Explanation

The correct answer is that Na is important to initiate the pacemaker action potential, but it is not important for its maintenance. This means that Na channels play a crucial role in depolarizing the membrane and initiating the action potential in pacemaker cells. However, once the action potential is initiated, other ion channels, such as Ca and K channels, are primarily responsible for maintaining and repolarizing the membrane potential.

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11.

Regarding the cardiac muscle action potential, which of the following is not true:

The initial repolarization is due to K efflux
The plateau is due to balance between the Ca, K mobility
The complete repolariztion is at the end of phase 3 when all K is effluxed
Na is an important ion for depolarization
None of the above

Correct Answer

A. The complete repolariztion is at the end of phase 3 when all K is effluxed

Explanation

The complete repolarization does not occur at the end of phase 3 when all K is effluxed. Instead, the complete repolarization occurs when the K channels close and the membrane potential returns to its resting state.

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Dr Gawad Physiology Course Online Exam - CVS – Course Lecture 1- Introduction, Rhythmicity,

The cardiac muscle fibres :

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About the pacemaker potential, all the following is true except:

S.A.N. is the normal pacemaker because:

The pacemaker potential un-stability is due primarily to:

The steepest prepotenial normally occurs in the:

Intrinsic heart rate refers to:

The main cause of plateau in cardiac muscle action potential:

Which of the following is considered as an ectopic pacemaker:

Regarding the differences between cardiac muscle and pace maker action potentials, which of the following is true:

Regarding pacemaker action potential which is true:

Regarding the cardiac muscle action potential, which of the following is not true: