Podcast
Questions and Answers
What causes the pacemaker potential in the SAN during phase 4?
What causes the pacemaker potential in the SAN during phase 4?
- Increased influx of Mg2+ ions
- Increased efflux of Cl- ions
- K+ influx through leak channels
- Na influx through funny channels (correct)
Which phase of the SAN action potential is characterized by depolarization from -40 mv to +10 mv?
Which phase of the SAN action potential is characterized by depolarization from -40 mv to +10 mv?
- Phase 1
- Phase 0 (correct)
- Phase 3
- Phase 2
What primarily leads to the repolarization of the SAN during phase 3?
What primarily leads to the repolarization of the SAN during phase 3?
- Increased Na+ influx
- Increased K+ efflux (correct)
- Increased Cl- influx
- Decreased Ca2+ influx (correct)
What effect does sympathetic stimulation have on SAN rhythmicity?
What effect does sympathetic stimulation have on SAN rhythmicity?
What is the effect of mild vagal stimulation on sinus rhythm?
What is the effect of mild vagal stimulation on sinus rhythm?
How does moderate warming affect the rhythmicity of the SAN?
How does moderate warming affect the rhythmicity of the SAN?
Which of the following factors reduces the rhythmicity of the SAN?
Which of the following factors reduces the rhythmicity of the SAN?
What is a positive chronotropic factor?
What is a positive chronotropic factor?
What is the main origin of rhythmicity in the heart?
What is the main origin of rhythmicity in the heart?
Which structure in the heart has the highest intrinsic rhythm rate?
Which structure in the heart has the highest intrinsic rhythm rate?
What is the primary purpose of the properties of cardiac muscle such as contractility and excitability?
What is the primary purpose of the properties of cardiac muscle such as contractility and excitability?
What is the resting membrane potential (RMP) of the Sinoatrial Node (SAN) cells?
What is the resting membrane potential (RMP) of the Sinoatrial Node (SAN) cells?
Which phase of the action potential in the SAN corresponds to the gradual rise in membrane potential from -55/-60 mv to -40 mv?
Which phase of the action potential in the SAN corresponds to the gradual rise in membrane potential from -55/-60 mv to -40 mv?
What characteristic does NOT describe the rhythmicity of the heart?
What characteristic does NOT describe the rhythmicity of the heart?
What is the resting state of the cardiac muscle often referred to as?
What is the resting state of the cardiac muscle often referred to as?
What happens to the SAN's action potential when the Na+ permeability increases?
What happens to the SAN's action potential when the Na+ permeability increases?
What is the primary effect of an increase in body temperature on heart rate?
What is the primary effect of an increase in body temperature on heart rate?
Which of the following factors typically decreases cardiac rhythmicity?
Which of the following factors typically decreases cardiac rhythmicity?
What effect does hypoxia (reduced oxygen) have on cardiac rhythmicity?
What effect does hypoxia (reduced oxygen) have on cardiac rhythmicity?
The Faget sign is characterized by which of the following?
The Faget sign is characterized by which of the following?
Which ions are critical for normal heart function by affecting the cardiac rhythmicity?
Which ions are critical for normal heart function by affecting the cardiac rhythmicity?
What is the primary role of the sinoatrial node (SAN) in heart function?
What is the primary role of the sinoatrial node (SAN) in heart function?
What mechanism does digitalis use to affect heart rhythm?
What mechanism does digitalis use to affect heart rhythm?
What is the effect of acidosis on the affinity of catecholamines for cardiac receptors?
What is the effect of acidosis on the affinity of catecholamines for cardiac receptors?
What initiates the action potential in the cardiac impulse transmission process?
What initiates the action potential in the cardiac impulse transmission process?
What is the velocity of the cardiac impulse transmission in the atria?
What is the velocity of the cardiac impulse transmission in the atria?
Which of the following is NOT a cause of AVN delay?
Which of the following is NOT a cause of AVN delay?
What allows sufficient time for the atria to empty their blood into the ventricles?
What allows sufficient time for the atria to empty their blood into the ventricles?
What is the characteristic velocity of the Purkinje system during impulse transmission?
What is the characteristic velocity of the Purkinje system during impulse transmission?
Which factor is NOT associated with the rapid conduction in the Purkinje system?
Which factor is NOT associated with the rapid conduction in the Purkinje system?
In which direction does the AV bundle conduct impulses?
In which direction does the AV bundle conduct impulses?
What is the speed of impulse transmission through ventricular muscle?
What is the speed of impulse transmission through ventricular muscle?
Study Notes
Cardiac Physiology Overview
- The heart's action potential is characterized by three phases:
- Resting Membrane Potential (RMP): Polarized state before action potential begins.
- Depolarization: Triggered by Na+ influx.
- Repolarization: Followed by K+ efflux restoring RMP.
Properties of Cardiac Muscle
- Four essential properties for heart function:
- Rhythmicity: Heart beats regularly; myogenic origin—doesn't require neural initiation.
- Excitability: Cardiac muscle's response to stimuli.
- Conductivity: Ability to transmit electrical impulses.
- Contractility: Ability to contract and pump blood.
Rhythmicity
- Defined as the regular beating of the heart.
- Origin: Myogenic; heart beats before nerve development in a fetus and continues in transplanted hearts.
- Self-excitation: Natural properties of nodal (SA node, AV node) and conducting fibers (e.g., Purkinje fibers).
- Heart Rate:
- SA Node: ~110 beats/min
- AV Node: ~90 beats/min
- Bundle Branches: ~45 beats/min
- Purkinje Fibers: ~35 beats/min
- Ventricles: ~25 beats/min
Mechanism of Rhythmicity (SAN Action Potential)
- Pacemaker Potential (Phase 4):
- Gradual rise in membrane potential due to Na+ influx and Ca2+ influx.
- Causes diastolic depolarization.
- Depolarization (Phase 0):
- Membrane potential from -40 mV to +10 mV through Ca2+ influx.
- Repolarization (Phase 3):
- Ca2+ influx ceases; K+ efflux returns potential to RMP.
Factors Affecting Rhythmicity
- Nervous Factors:
- Sympathetic stimulation increases rhythmicity; vagal stimulation decreases it.
- Physical Factors:
- Moderate warming enhances rhythmicity; excessive warming or cooling can reduce it.
- Chemical Factors:
- Catecholamines increase; cholinergic drugs and high K+ levels decrease rhythmicity.
- Blood gas effects: O2 decrease improves rhythmicity; CO2 increase and H+ concentration changes can impair it.
- Balanced Na+, K+, and Ca2+ ion levels are crucial for rhythmicity.
Conductivity
- Defined as the heart's ability to conduct excitation waves.
- Impulse Transmission:
- Starts from the SA Node.
- Travels through atria, AV Node (with a notable delay), Purkinje system, and into the ventricular muscle.
Phases of Impulse Transmission
- Through Atria:
- Action potential travels at approximately 1 m/sec.
- Through AV Node:
- Delayed transmission at 0.02-0.05 m/sec; delay allows atrial emptying into ventricles.
- Through Purkinje System:
- Rapid conduction at about 4 m/sec; large fibers enhance speed.
- In Ventricular Muscle:
- Transmission speed of 0.3-0.5 m/sec.
Factors Affecting Conductivity
- Influenced by the same factors that affect rhythmicity.
- Dromotropism:
- Positive factors increase conductivity; negative factors decrease it.
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Description
This quiz covers the fundamentals of cardiac physiology, focusing on the action potential and essential properties of cardiac muscle. Understand the phases of the heart’s electrical activity and the significance of rhythmicity, excitability, conductivity, and contractility in heart function.
