Cardiac Conduction System Overview

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Questions and Answers

What is another name for the subendocardial conducting network?

AV bundle

Bundle of His

SA node

Purkinje fibers (correct)

Where is the subendocardial conducting network most elaborate?

Right ventricle

Left side of the heart (correct)

Right atrium

Interventricular septum

What occurs immediately after depolarization at the apex of the heart?

SA node firing

Atrial contraction

Ventricular relaxation

Ventricular contraction (correct)

What can result from defects in the intrinsic conduction system?

Arrhythmias Signup and view all the answers

What is the range of beats per minute if the AV node takes over pacing?

40–60 beats/min Signup and view all the answers

What is the purpose of defibrillation?

To restore heartbeat after cardiac arrest Signup and view all the answers

What is an extrasystole?

A premature contraction caused by ectopic focus Signup and view all the answers

What can excessive caffeine or nicotine lead to in heart function?

Extrasystoles Signup and view all the answers

What is the function of the AV node in cardiac conduction?

It acts as a relay to transmit impulses to the ventricles. Signup and view all the answers

What can occur if there is a total block at the AV node?

Ventricles may continue with their intrinsic beating. Signup and view all the answers

What ionic change primarily initiates the rising phase of the action potential in contractile cardiac muscle cells?

Fast voltage-gated Na+ influx Signup and view all the answers

Which center in the medulla oblongata is responsible for increasing heart rate and force?

Cardioacceleratory center Signup and view all the answers

What happens to the action potential during the plateau phase in cardiac muscle contraction?

Ca2+ channels open while Na+ channels are closed. Signup and view all the answers

What purpose does an artificial pacemaker serve in the heart?

It coordinates the contraction between atria and ventricles. Signup and view all the answers

How are calcium ions handled following the plateau phase of the action potential in cardiac muscle cells?

They are pumped back into the sarcoplasmic reticulum and out of the cell. Signup and view all the answers

What is a characteristic feature of cardiac muscle contraction that distinguishes it from skeletal muscle contraction?

Cardiac muscle shows a plateau in action potentials. Signup and view all the answers

What percentage of blood flows into the ventricles passively during ventricular filling?

80% Signup and view all the answers

What event triggers atrial systole?

Atrial depolarization Signup and view all the answers

What is the term for the blood volume in each ventricle at the end of ventricular diastole?

End diastolic volume (EDV) Signup and view all the answers

During isovolumetric contraction, what causes the closing of the AV valves?

Rising ventricular pressure Signup and view all the answers

What is the primary characteristic of the isovolumetric contraction phase?

Ventricles are completely closed and volume remains constant Signup and view all the answers

What happens during isovolumetric relaxation?

Ventricles relax while all valves are closed Signup and view all the answers

What triggers the closing of the SL valves during isovolumetric relaxation?

Backflow of blood from the aorta Signup and view all the answers

What does the end systolic volume (ESV) represent?

Blood volume in the ventricles post contraction Signup and view all the answers

What phenomenon is referred to as the dicrotic notch?

Closure of the aortic valve raising aortic pressure Signup and view all the answers

How long does the quiescent period last in the cardiac cycle?

0.4 seconds Signup and view all the answers

What causes the first heart sound (lub)?

Closing of the AV valves Signup and view all the answers

What type of valve issue causes a swishing sound due to backflow of blood?

Incompetent valve Signup and view all the answers

What is the duration of ventricular systole in the cardiac cycle?

0.3 seconds Signup and view all the answers

Which heart valve closes slightly before the other during the cardiac cycle?

Mitral valve closes slightly before tricuspid valve Signup and view all the answers

What sound does a stenotic valve typically produce?

High-pitched sound or clicking Signup and view all the answers

What is a common cause of heart murmurs?

Obstruction due to valve problems Signup and view all the answers

Which hormone is known to increase heart rate and contractility?

Epinephrine Signup and view all the answers

What effect does hypocalcemia have on heart function?

Depresses heart function Signup and view all the answers

What factor is NOT typically associated with an increase in heart rate?

Cold temperature Signup and view all the answers

What is tachycardia defined as?

Heart rate faster than 100 beats/min Signup and view all the answers

Which condition is characterized by inadequate blood circulation due to low cardiac output?

Congestive heart failure Signup and view all the answers

How does hyperkalemia affect heart function?

Alters electrical activity of the heart Signup and view all the answers

Which demographic typically shows a faster heart rate?

Females Signup and view all the answers

Which ion concentration is critical to maintain for normal heart function?

Calcium (Ca2+) Signup and view all the answers

Study Notes

Intrinsic Conduction System

Purkinje fibers create complete pathway in heart
More elaborate on the left side
Depolarize 30 times per minute with no AV node input
Ventricular contraction follows from apex to atria

Cardiac Conduction System Disturbances

May cause arrhythmias, uncoordinated contractions, fibrillation
Fibrillation is rapid irregular contractions, results in no blood pumping
Defibrillation interrupts the chaotic twitching and allows heart to restart
Defective SA node may result in junctional rhythm
Extrasystole is when a small part of the heart triggers an event
Heart has more time to fill, next contraction is felt as strong thud
Caffeine and nicotine can cause extrasystole
Heart block is when the AV node is defective
Impulse cannot reach ventricle or only a few get through
Treatment involves artificial pacemaker

Extrinsic Innervation of the Heart

Cardiac centers in medulla oblongata modify heartbeat
Cardioacceleratory center increases heart rate and force
Cardioinhibitory center decreases heart rate

Contractile Cardiac Muscle Cells

Cardiac muscle cells contain plateau phase
Fast voltage-gated Na+ channels open, Na+ enters cell
Slow Ca2+ channels open after Na+ depolarization
Ca2+ channels close after 200 ms, while K+ channels open

Mechanical Events of the Heart

Ventricular filling is from mid-to-late diastole, 80% passively
Atrial systole pushes the remaining 20% of blood into ventricles
End diastolic volume is blood volume during ventricular diastole
Isovolumetric contraction is when ventricles contract and AV valves close
End systolic volume is the blood volume remaining after systole
Isovolumetric relaxation is when ventricles relax and close
Heart beat is about 75 beats per minute
Cardiac cycle lasts about 0.8 seconds

Heart Sounds

Lub-dup sounds are caused by valves closing
First sound is AV valve closing, second sound is SL valve closing
Pause between lub-dup is the heart relaxing
Mitral valve closes before tricuspid and aortic closes before pulmonary

Heart Murmurs

Murmurs are abnormal sounds caused by blood hitting obstructions
Incompetent valves don't close completely, causing backflow, a swishing sound
Stenotic valves don't open completely, restrict flow causing high-pitched sound

Regulation of Heart Rate

Epinephrine increases heart rate and contractility
Thyroxine increases heart rate and enhances epinephrine, norepinephrine
Ca2+ and K+ imbalances affect heart function
Hypocalcemia depresses the heart
Hypercalcemia increases heart rate and contractility
Hyperkalemia alters electrical activity- can cause heart block
Hypokalemia leads to feeble heartbeat and arrhythmias
Age affects heart rate
Gender affects heart rate
Exercise influences heart rate
Body temperature influences heart rate

Heart Rate Imbalances

Tachycardia is heart rate above 100 beats per minute
Bradycardia is heart rate below 60 beats per minute

Cardiac Output Imbalances

Congestive heart failure is when CO is insufficient to meet tissue needs
Coronary atherosclerosis impairs oxygen delivery to cardiac cells
Heart becomes hypoxic and contracts inefficiently

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Description

Explore the intricacies of the cardiac conduction system, including the intrinsic conduction pathways and potential disturbances that can lead to arrhythmias. This quiz covers essential concepts like Purkinje fibers, heart block, and the influence of external factors on heart rhythm. Test your knowledge of cardiac physiology and learn how different factors can affect heart performance.