Regulation of Heart Function Quiz

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Questions and Answers

What effect does parasympathetic stimulation have on the heart's depolarization phase?

  • It prolongs the time taken to reach depolarization. (correct)
  • It creates a plateau phase.
  • It accelerates depolarization.
  • It increases conduction velocity.

Which of the following components is primarily responsible for increasing heart rate upon sympathetic stimulation?

  • PKA.
  • LTCC.
  • cAMP.
  • If channels. (correct)

What is the primary effect of parasympathetic stimulation on heart rate?

  • It decreases heart rate. (correct)
  • It maintains heart rate.
  • It increases heart rate.
  • It causes irregular heartbeats.

How does the sympathetic nervous system affect conduction velocity in nodal cells?

<p>It increases conduction velocity. (C)</p> Signup and view all the answers

What is the primary consequence of increased If activity in the SA node?

<p>Increased heart rate. (C)</p> Signup and view all the answers

Which neurotransmitter is secreted during parasympathetic stimulation?

<p>Acetylcholine (D)</p> Signup and view all the answers

What role does cAMP play in sympathetic stimulation of nodal cells?

<p>It activates PKA, enhancing heart activity. (D)</p> Signup and view all the answers

What law describes the intrinsic regulation of heart function?

<p>Starling’s law (B)</p> Signup and view all the answers

What happens to the slope of Phase 4 during sympathetic stimulation?

<p>It increases. (B)</p> Signup and view all the answers

What is the effect of sympathetic stimulation on heart rate and contraction force?

<p>It increases both heart rate and force of contraction. (B)</p> Signup and view all the answers

Which protein is associated with the positive chronotropic effect in nodal cells?

<p>PKA. (C)</p> Signup and view all the answers

Which channel is affected by acetylcholine during parasympathetic control?

<p>K+/ACh channel (C)</p> Signup and view all the answers

How does the activity of the If channel affect the heart rate?

<p>Decreases heart rate by decreasing the Phase 4 slope. (A)</p> Signup and view all the answers

Which effect best describes the (-) dromotropic effect?

<p>Slower conduction of action potentials. (D)</p> Signup and view all the answers

What is primarily lowered during parasympathetic stimulation?

<p>All of the above. (D)</p> Signup and view all the answers

What role does norepinephrine play in sympathetic stimulation?

<p>Increases heart rate and force of contraction. (C)</p> Signup and view all the answers

Which type of receptors are primarily involved in parasympathetic control on nodal cells?

<p>m2 muscarinic receptors (A)</p> Signup and view all the answers

Which neurotransmitters are involved in sympathetic control of nodal cells?

<p>Epinephrine and norepinephrine. (C)</p> Signup and view all the answers

What effect does sympathetic stimulation have on cAMP levels in nodal cells?

<p>Increases cAMP levels. (A)</p> Signup and view all the answers

What is the physiological response when the heart's K+/ACh channel activity increases?

<p>Heart rate decreases. (D)</p> Signup and view all the answers

What effect does sympathetic stimulation have on the heart's conduction velocity?

<p>Increases conduction velocity (C)</p> Signup and view all the answers

Which type of agents positively affect contractility in cardiac contractile cells?

<p>Epinephrine and Norepinephrine (B)</p> Signup and view all the answers

What is the primary factor that determines heart rate?

<p>Rate of depolarization in autorhythmic cells (A)</p> Signup and view all the answers

Which type of effect is associated with changes in heart rate?

<p>Chronotropic effect (A)</p> Signup and view all the answers

What is the effect of a positive dromotropic agent on conduction velocity through the AV node?

<p>Increases conduction velocity (A)</p> Signup and view all the answers

Which physiological process increases stroke volume during sympathetic stimulation?

<p>Increased contractility (D)</p> Signup and view all the answers

What effect does sympathetic stimulation exert on the duration of ventricular diastole?

<p>Decreases duration of diastole (C)</p> Signup and view all the answers

How does the intrinsic regulation of the heart differ from extrinsic regulation?

<p>Intrinsic regulation is controlled by the heart's own pacemaker cells (C)</p> Signup and view all the answers

Which protein inhibits the SERCA2 pump in cardiac contractile cells?

<p>Phospholamban (B)</p> Signup and view all the answers

What is the relationship between venous return and stroke volume during sympathetic activation?

<p>Increased venous return increases stroke volume (C)</p> Signup and view all the answers

Flashcards

Intrinsic heart regulation

Heart function regulated by its inherent characteristics, not external factors like nerves or hormones.

Extrinsic heart regulation

Heart function regulated by nerves and hormones.

Starling's Law of the Heart

The heart's ability to adjust its output based on the volume of blood entering it.

Parasympathetic stimulation

Heart rate slowed by the vagus nerve, releasing acetylcholine.

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Sympathetic stimulation

Increases heart rate and contraction force via cardiac nerves, releasing epinephrine and norepinephrine.

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Vagus nerve

A nerve that slows down the heart rate.

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Acetylcholine

Neurotransmitter that slows heart rate.

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Epinephrine/Norepinephrine

Neurotransmitters that increase heart rate and strength of contraction.

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Chronotropic effect

Effect on heart rate.

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Cardiac Nerves

Nerves carrying signals to regulate heartbeat.

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What does a positive chronotropic effect do?

A positive chronotropic effect increases heart rate.

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What does a negative chronotropic effect do?

A negative chronotropic effect decreases heart rate.

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What does a negative dromotropic effect do?

A negative dromotropic effect decreases conduction velocity through the heart.

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What is the effect of sympathetic stimulation on cardiac contractile cells?

Sympathetic stimulation increases contractility by activating the Gs protein pathway, which leads to increased calcium release and uptake by the SR, ultimately enhancing the force of contraction.

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What is an inotropic effect?

An inotropic effect influences the contractility of the heart.

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What is the relationship between stroke volume and heart rate?

Stroke volume and heart rate are the two factors that determine cardiac output.

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How does venous return affect stroke volume?

Increased venous return increases end-diastolic volume, which in turn increases stroke volume.

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How does sympathetic innervation and epinephrine influence cardiac contractility?

Sympathetic innervation and epinephrine increase contractility by activating the Gs protein pathway, leading to increased calcium release and uptake by the SR, ultimately enhancing the force of contraction.

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LTCC Activity in Phase 0

LTCC activity has a slower depolarization rate, leading to a decreased conduction velocity in Phase 0.

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Parasympathetic Control on the Heart

Parasympathetic stimulation hyperpolarizes the membrane potential and slows down depolarization in the heart, reducing heart rate.

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Sympathetic Control on Nodal Cells

Sympathetic control on nodal cells activates Gs protein, increasing cAMP, and activates PKA.

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If Activity (funny current)

Increased If activity from sympathetic control causes faster reaching of the threshold in phase 4 and increased heart rate.

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Phase 4 Slope

Phase 4 slope refers to the rate at which the membrane potential rises in Phase 4.

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Membrane Potential

The difference in electrical charge across a cell's membrane.

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Heart Rate (HR)

The number of times the heart beats per minute.

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Threshold (VT)

The critical level of membrane potential that initiates an action potential.

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Study Notes

Regulation of Heart Function

  • Intrinsic regulation arises from the normal functioning of the heart, independent of neural or hormonal control.
  • Starling's Law of the Heart is a key concept in intrinsic regulation.
  • Extrinsic regulation involves controlling the heart via neural and hormonal signals.
  • Parasympathetic stimulation, mediated by the vagus nerve, slows heart rate by releasing acetylcholine.
  • Sympathetic stimulation, via cardiac nerves, increases heart rate and contractility by releasing epinephrine and norepinephrine.
  • Cardiac innervation: Parasympathetic and sympathetic pathways regulate the heart's rhythm and contractility.

Parasympathetic Control on Nodal Cells

  • Parasympathetic activity reduces the slope of phase 4, hyperpolarizing nodal cells and slowing heart rate.
  • It increases potassium channel activity and thus, reduces heart rate.
  • This decreases the rate of spontaneous depolarization (phase 4) and prolongs the time to reach threshold.
  • The slowed depolarization decreases heart rate and conduction velocity.

Sympathetic Control on Nodal Cells

  • Sympathetic activity increases the slope of phase 4, speeding up the heart rate.
  • It enhances the activity of the If channel, leading to a faster rate of spontaneous depolarization.
  • This faster depolarization leads to faster heart rate and conduction velocity.

Extrinsic Regulation: Parasympathetic Control

  • Parasympathetic stimulation causes a hyperpolarized state.
  • The depolarization phase becomes slower compared to the normal heart rate.

Extrinsic Regulation: Sympathetic Control

  • Sympathetic stimulation causes a steeper and faster depolarization phase.

Types of Effects: Chronotropic Effect

  • Chronotropic effect relates to changes in heart rate.
  • Increased sympathetic stimulation leads to an increase in heart rate (positive chronotropic).
  • Parasympathetic stimulation leads to a decrease in heart rate (negative chronotropic).

Types of Effects: Dromotropic Effect

  • Dromotropic effects involve changes in conduction velocity across the heart.
  • Sympathetic stimulation speeds up conduction.
  • Parasympathetic stimulation slows conduction.

Types of Effects: Inotropic Effect

  • Inotropic effects modify cardiac contractility.
  • Positive inotropic effect increases contractility (eg. Epinephrine, Norepinephrine).
  • Negative inotropic effect decreases contractility (eg. certain chemicals).

Stroke Volume and Heart Rate

  • Stroke volume is the volume pumped by the heart with each beat.
  • Heart rate is the number of beats per minute.
  • Cardiac output is the product of stroke volume and heart rate.
  • Factors affecting stroke volume include contractility, end-diastolic volume, and venous return.
  • Factors affecting heart rate include sympathetic and parasympathetic inputs.

Wiggers Diagram

  • A graphical representation of the cardiac cycle, showing relationships between pressure, volume, and electrical activity.
  • The diagram illustrates the phases of the cardiac cycle and the associated changes in ventricular pressure, volume, and electrical activity.
  • Shows the relationship between heart sounds, electrical signals, pressure, and volume changes within the heart during one cardiac cycle.

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