Cardiac Cycle: Electrical Events and ECG Trace

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Questions and Answers

Which structure transmits the action potential with a 0.1 second delay, allowing full atrial contraction?

  • Purkinje fibers
  • SA node
  • AV node (correct)
  • AV bundle (bundle of HIS)

In the sequence of events during the cardiac cycle, where does the action potential pass through after the AV node?

  • Left bundle branch
  • Right bundle branch
  • Purkinje fibers
  • SA node (correct)

What is the name of the extensive network that spreads through the ventricular myocardium from the apex upwards?

  • AV bundle (bundle of HIS)
  • SA node
  • AV node
  • Purkinje fibers (correct)

Which of the following structures is responsible for generating the action potential in the right atrium?

<p>SA node (C)</p> Signup and view all the answers

What is the function of the AV bundle (bundle of HIS) in the transmission of the action potential?

<p>Generates the action potential in the right atrium (A)</p> Signup and view all the answers

Which part of the heart completes depolarization after being innervated by the Purkinje fibers?

<p>Left ventricle (C)</p> Signup and view all the answers

What comprises the diastole of the cardiac cycle?

<p>Isovolumetric ventricular relaxation and ventricular filling with atria relaxed (C)</p> Signup and view all the answers

What is the effect of sympathetic input on the heart rate?

<p>Increases the heart rate (B)</p> Signup and view all the answers

Which hormones and ions can increase the heart rate?

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

What is the primary determinant of arterial blood pressure?

<p>Elastic properties of the arterial system (A)</p> Signup and view all the answers

What is the formula for cardiac output (CO)?

<p>$CO = SV imes HR$ (B)</p> Signup and view all the answers

What does an inotrope affect in relation to the heart?

<p>Force of contraction (B)</p> Signup and view all the answers

What is the main determinant of arterial blood pressure?

<p>Resistance to forward flow in the arterial system (A)</p> Signup and view all the answers

What factor influences vascular resistance (R) the most?

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

In the pulmonary circulation, which chamber generates less force compared to the systemic circulation?

<p>Right ventricle (C)</p> Signup and view all the answers

Which part of the brain controls both heart rate and blood pressure?

<p>Medulla oblongata (A)</p> Signup and view all the answers

What is the normal range of ejection fraction, a measure of cardiac function?

<p>$60-70 ext{%}$ (D)</p> Signup and view all the answers

Which wave in an ECG represents atrial depolarization?

<p>P wave (A)</p> Signup and view all the answers

What does the QRS complex in an ECG represent?

<p>Ventricular depolarization (C)</p> Signup and view all the answers

What does the T-Q segment in an ECG represent?

<p>Ventricular diastole (C)</p> Signup and view all the answers

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Study Notes

Cardiac Cycle

  • The AV node transmits the action potential with a 0.1 second delay, allowing full atrial contraction.
  • After the AV node, the action potential passes through the AV bundle (Bundle of His).

Electrical Conduction System

  • The Purkinje fibers innervate the ventricular myocardium, allowing it to depolarize.
  • The extensive network that spreads through the ventricular myocardium from the apex upwards is called the Purkinje fibers.
  • The sinoatrial (SA) node is responsible for generating the action potential in the right atrium.

Transmission of Action Potential

  • The AV bundle (Bundle of His) transmits the action potential from the AV node to the ventricular myocardium.

Cardiac Function

  • Diastole is the period of the cardiac cycle where the heart muscle relaxes.
  • Sympathetic input increases the heart rate.
  • Hormones such as epinephrine and norepinephrine, and ions such as calcium, increase the heart rate.
  • Cardiac output (CO) is calculated using the formula CO = Heart Rate x Stroke Volume.
  • An inotrope affects the contractility of the heart.

Blood Pressure Regulation

  • The primary determinant of arterial blood pressure is peripheral resistance.
  • The main determinant of arterial blood pressure is total peripheral resistance.
  • Vascular resistance (R) is most influenced by the Diameter of blood vessels.
  • The brain stem, specifically the medulla oblongata, controls both heart rate and blood pressure.

Pulmonary Circulation

  • The right ventricle generates less force compared to the left ventricle in the systemic circulation.

ECG

  • The P wave in an ECG represents atrial depolarization.
  • The QRS complex in an ECG represents ventricular depolarization.
  • The T-Q segment in an ECG represents ventricular repolarization.
  • The normal range of ejection fraction, a measure of cardiac function, is 55-70%.

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