Conduction of the Action Potential in the Heart

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Questions and Answers

What is the effect of the sympathetic nervous system on heart rate?

Positive chronotropic effect (correct)

No effect on heart rate

Increases heart rate followed by a decrease

Negative chronotropic effect

How does the parasympathetic nervous system decrease heart rate?

By increasing the conductance of Ca2+ channels in the SA node

By decreasing the conductance of K+ channels and decreasing Ca2+ channels in the SA node (correct)

By decreasing the conductance of K+ channels in the SA node

By increasing the rate of phase 4 depolarization in the SA node

What is the effect of the parasympathetic nervous system on heart rate?

Negative chronotropic effect (correct)

Positive chronotropic effect

No effect on heart rate

First increases then decreases heart rate

How does the sympathetic nervous system increase heart rate?

By increasing the conductance of K+ channels and increasing Ca2+ channels in the SA node Signup and view all the answers

What is the effect of the parasympathetic nervous system on conduction velocity?

Decreases conduction velocity Signup and view all the answers

What is the effect of the sympathetic nervous system on conduction velocity?

Increases conduction velocity Signup and view all the answers

What is the effect of activating β1 receptors in the SA node?

Increase in If, resulting in faster phase 4 depolarization Signup and view all the answers

What is the impact of increased ICa due to activation of β1 receptors in the SA node?

More functional Ca2+ channels, requiring more depolarization to reach threshold Signup and view all the answers

What is the consequence of damage to the conduction system within the heart?

Decreased ability of the ventricles to generate pressure Signup and view all the answers

How does activation of β1 receptors affect heart rate?

Increases heart rate by increasing SA node firing frequency Signup and view all the answers

What is the role of increased If in the SA node upon activation of β1 receptors?

More frequent reaching of threshold potential Signup and view all the answers

How does damage to the conducting system within the heart relate to arrhythmias?

Damage can precipitate arrhythmias due to altered conduction pathways Signup and view all the answers

What is the effect of the sympathetic nervous system on conduction velocity through the AV node?

Increases conduction velocity (positive dromotropic effect) Signup and view all the answers

How does the sympathetic nervous system increase conduction velocity through the AV node?

By increasing the inward calcium current ($I_{Ca}$) Signup and view all the answers

What is the effect of the parasympathetic nervous system on conduction velocity through the AV node?

Decreases conduction velocity (negative dromotropic effect) Signup and view all the answers

How does the parasympathetic nervous system decrease conduction velocity through the AV node?

By increasing the outward potassium current ($I_{K-ACh}$) Signup and view all the answers

What is the physiological importance of the autonomic nervous system's effect on conduction velocity through the AV node?

All of the above Signup and view all the answers

Which of the following statements is true regarding the effects of the autonomic nervous system on heart rate and conduction velocity?

The sympathetic nervous system increases both heart rate and conduction velocity Signup and view all the answers

Study Notes

Effects of the Autonomic Nervous System (ANS) on Heart Rate (HR)

Sympathetic Nervous System (SNS) has a positive chronotropic effect on HR, increasing the rate of phase 4 depolarization and heart rate.
- Increases cAMP, which increases If and the rate of phase 4 depolarization.
- Increases ICa, which means there are more functional Ca2+ channels and thus less depolarization is required to reach threshold potential.
Parasympathetic Nervous System (PNS) has a negative chronotropic effect on HR, decreasing the rate of phase 4 depolarization and heart rate.
- Decreases cAMP, which decreases If and the rate of phase 4 depolarization.
- Increases IK-ACh, which hyperpolarizes the Vm, making it more difficult to reach threshold potential.
- Decreases ICa, which means there are fewer functional Ca2+ channels and thus more depolarization is required to reach threshold potential.

Effects of the ANS on Conduction Velocity (CV)

SNS has a positive dromotropic effect on CV, increasing the rate at which action potentials are conducted from the atria to the ventricles.
- Increases Ica, which increases inward current and CV.
- Shortens the effective refractory period (ERP), allowing for shorter recovery from inactivation and increased CV.
PNS has a negative dromotropic effect on CV, decreasing the rate at which action potentials are conducted from the atria to the ventricles.
- Decreases Ica, which decreases inward current and CV.
- Increases IK-ACh, which increases outward K+ current and decreases CV.
- Lengthens the ERP, allowing for longer recovery from inactivation and decreased CV.

Physiological Importance of ANS Effects on CV

If CV through the AV node is slowed sufficiently, some action potentials may not be conducted at all from the atria to the ventricles, producing heart block.
The degree of heart block may vary, ranging from slowed conduction to complete heart block.

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Description

Learn about the importance of the normal functioning conduction system in the heart for rapid, organized depolarization and coordinated contraction of ventricular myocytes. Understand how efficient conduction ensures smooth ejection of blood and proper pressure generation during ventricular contraction.