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

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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.

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.

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.

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.

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.

The correct answer is "Form true syncytium." Cardiac muscle fibers are unique in that they are interconnected through intercalated discs, forming a syncytium. This allows for coordinated contraction of the entire heart, ensuring efficient pumping of blood. Unlike skeletal muscle fibers, cardiac muscle fibers are striated and have a high concentration of mitochondria to support their continuous contraction. Additionally, they have low resistance bridges and tight gap junctions, which facilitate rapid electrical conduction between cells.

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.

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."

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.

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.