Heart Physiology and Function

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Questions and Answers

Which of the following pacemakers has the highest intrinsic firing rate in the heart?

AV Node

SA Node (correct)

Contractile Cells

Purkinje Fibers

What is the inherent firing rate of the AV Node?

70 bpm

30 bpm

90 bpm

50 bpm (correct)

Which structure is responsible for the rapid conduction of depolarization to the apex of the heart?

Purkinje Fibers

AV Bundle (correct)

Internodal Pathways

AV Node

What happens to the conduction velocity as depolarization spreads across the atria?

It slows down significantly Signup and view all the answers

Which structure can depolarize on its own if all other pacemakers fail?

Purkinje Fibers Signup and view all the answers

During an electrocardiogram (ECG), which wave represents ventricular depolarization?

QRS Complex Signup and view all the answers

What is the possible heart rate if both the SA Node and AV Node are unable to function correctly?

30 bpm Signup and view all the answers

What is the most significant effect of conduction blocks in the heart?

Irregular heart rhythms Signup and view all the answers

What is the primary function of autorhythmic cells in the heart?

To set and regulate the pace of the heart rhythm Signup and view all the answers

Which structure is responsible for the fastest intrinsic pacing of the heart?

SA node Signup and view all the answers

Which of the following conditions would likely increase heart rate due to sympathetic stimulation?

Increased permeability to sodium and calcium Signup and view all the answers

How is cardiac output calculated?

CO (mL/min) = SV (mL) x HR (BPM) Signup and view all the answers

Which of the following alterations to the membrane potential would slow the heart rate?

Increased potassium ion influx Signup and view all the answers

What role does the ECG serve in assessing heart function?

Detection of heart rhythm disturbances and conduction blocks Signup and view all the answers

What is the Frank-Starling mechanism primarily associated with?

Intrinsic control of stroke volume based on muscle stretch Signup and view all the answers

What happens to the depolarization process during parasympathetic stimulation?

It slows down due to hyperpolarization Signup and view all the answers

Which of the following best describes stroke volume regulation?

Influenced by intrinsic properties and sympathetic modulation Signup and view all the answers

What is the primary effect of norepinephrine on autorhythmic cells?

Increased permeability to calcium and faster depolarization Signup and view all the answers

What is the primary role of autorhythmic cells in the heart?

They generate action potentials that set the pace of the heart. Signup and view all the answers

Where are the fastest autorhythmic cells located within the heart?

SA node Signup and view all the answers

Which feature prevents summation of force in cardiac muscle contractions?

Long refractory period Signup and view all the answers

What effect does damage to the SA node typically have on heart function?

Arrhythmia or irregular heart rhythms Signup and view all the answers

What does an ECG primarily detect?

Changes in heart rate and rhythm Signup and view all the answers

What is the resting potential characteristic of contractile cells?

Stable and consistent Signup and view all the answers

How does calcium contribute to the action potential of contractile cells?

It causes rapid depolarization during the action potential. Signup and view all the answers

What are the intercalated disks primarily responsible for in cardiac tissue?

Transmitting electrical signals and force between cells Signup and view all the answers

What is one consequence of conduction blocks in the heart?

Potential arrhythmias or missed beats Signup and view all the answers

What happens during the long refractory period in cardiac muscle?

Cardiac cells cannot be re-excited. Signup and view all the answers

Which area of the heart is primarily responsible for initial electrical depolarization?

SA node Signup and view all the answers

What is the significance of graded potentials in contractile cells?

They aid in the transmission of force between cells. Signup and view all the answers

During which phase of the cardiac cycle does the heart muscle primarily relax?

Diastole Signup and view all the answers

What triggers the initiation of muscle contraction?

Binding of Ca2+ to troponin Signup and view all the answers

What occurs during the relaxation phase of muscle contraction?

Ca2+ unbinds from troponin Signup and view all the answers

Which mechanism is responsible for restoring Ca2+ levels back into the sarcoplasmic reticulum?

Ca2+ pumping by the sarcoplasmic reticulum Ca2+ ATPase Signup and view all the answers

What is the role of the Na+-K+-ATPase in muscle contraction?

It regulates the concentration of Na+ and K+ to maintain membrane potential Signup and view all the answers

How is the Ca2+ signal terminated in muscle cells?

By unbinding from troponin and being sequestered Signup and view all the answers

What characterizes sinus tachycardia in terms of heart rate?

Heart rate exceeds 100 beats per minute. Signup and view all the answers

Which of the following conditions is indicated by uncoordinated contraction of the atria?

Atrial fibrillation Signup and view all the answers

In which scenario does the AV node pace ventricular contractions?

When the SA node is blocked or fails. Signup and view all the answers

What does an ECG primarily help assess?

Heart rate and rhythm abnormalities. Signup and view all the answers

What is the main feature of an AV conduction block?

Delayed or absent signals to the AV node. Signup and view all the answers

During which scenario would atrial depolarization be considered disorganized?

Atrial fibrillation. Signup and view all the answers

In normal conditions, what should the heart rate reflect based on the sinoatrial (SA) node's function?

A variable rate typically between 60 to 100 beats per minute. Signup and view all the answers

Which component of an ECG reflects ventricular repolarization?

T wave Signup and view all the answers

Which statement correctly describes the conduction of electrical activity through the heart's conducting system?

Conduction slows significantly at the AV node compared to the atrial pathways. Signup and view all the answers

What is the consequence of the SA node failing to depolarize?

The AV node will take over pacemaking at 50 bpm. Signup and view all the answers

Which of the following correctly describes the firing rates of the heart's pacemakers?

SA node has the highest firing rate of 70 bpm compared to AV node and Purkinje fibers. Signup and view all the answers

What role do the internodal pathways serve during cardiac conduction?

They facilitate rapid transmission of impulses to the AV node from the SA node. Signup and view all the answers

What occurs after depolarization spreads rapidly through the ventricular conducting system?

A contraction wave spreads upward from the apex of the heart. Signup and view all the answers

How does the intrinsic firing rate of the AV node compare to that of the Purkinje fibers?

AV node's rate is higher at 50 bpm compared to Purkinje fibers' 30 bpm. Signup and view all the answers

In an electrocardiogram (ECG), where are the electrodes placed to measure electrical activity?

Attached to the skin surface of the right and left arms. Signup and view all the answers

What primarily dictates the heart's natural rhythm under normal circumstances?

The SA node sets the pace for heart contractions. Signup and view all the answers

What is the impact of parasympathetic stimulation on autorhythmic cells?

It leads to hyperpolarization and slower depolarization. Signup and view all the answers

How does sympathetic stimulation affect the heart's autorhythmic cells?

It causes an early opening of sodium channels. Signup and view all the answers

Which of the following describes how cardiac output (CO) is calculated?

CO is determined by multiplying stroke volume and heart rate. Signup and view all the answers

What role do the autorhythmic cells play in relation to heart rate?

They set the rate and rhythm of the heart through cyclical depolarization. Signup and view all the answers

How does the Frank-Starling mechanism affect stroke volume?

It increases stroke volume with an increase in venous return. Signup and view all the answers

What is the primary role of intercalated disks in cardiac muscle cells?

To allow electrical conduction between cells Signup and view all the answers

What is an immediate effect of increasing calcium ion permeability in contractile cells?

It enhances the calcium signal leading to stronger contractions. Signup and view all the answers

What happens to heart function if the SA node fails?

The AV node will take over as the primary pacemaker. Signup and view all the answers

What characteristic feature differentiates the action potentials of cardiac contractile cells from those of skeletal muscle cells?

They include a plateau phase Signup and view all the answers

What prevents the summation of force in cardiac muscle contractions?

Long refractory period Signup and view all the answers

What effect does the autonomic nervous system have on membrane potential in autorhythmic cells?

It influences the rate of depolarization by changing membrane permeability. Signup and view all the answers

What are the implications of calcium signaling in cardiac contractile cells?

Calcium signaling is essential for coordinated contraction. Signup and view all the answers

Which type of cells sets the rhythm and pace of the heart?

Autorhythmic cells Signup and view all the answers

During the action potential of autorhythmic cells, which ion primarily enters the cell first?

Sodium ($Na^{+}$) Signup and view all the answers

What is the outcome of a conduction block in the heart?

Decreased cardiac output due to impaired electrical signaling. Signup and view all the answers

Where are sutorhythmic cells mainly located within the heart?

At the SA node, AV node, and Purkinje fibers Signup and view all the answers

What causes the rapid depolarization phase in autorhythmic cells?

The opening of calcium channels Signup and view all the answers

Which of the following describes the resting potential of contractile cells in the heart?

Stable and controlled Signup and view all the answers

What feature of the electrocardiogram (ECG) assists in detecting conduction blocks in the heart?

QRS complex morphology Signup and view all the answers

Which phase of the cardiac action potential in contractile cells corresponds to opening calcium channels?

Phase 2 Signup and view all the answers

What is the physiological significance of graded potentials in cardiac contractile cells?

To synchronize contractions across the heart Signup and view all the answers

What type of muscle contraction resembles features of cardiac muscle contraction?

Smooth muscle contraction Signup and view all the answers

What initiates the electrical depolarization in the heart?

Spontaneous activity of pacemaker cells Signup and view all the answers

Study Notes

Autorhythmic Cells

Autorhythmic cells are responsible for the rhythm and pace of the heart.
They are located in the SA node, AV node, and Purkinje fibers.
The SA node is the fastest of the autorhythmic cells and sets the pace for the heart.

Electrocardiogram

ECGs can detect pathologies that affect heart rate, rhythm, conduction blocks, or coordination.
An ECG is measured by attaching electrodes to the skin surface.

Contractile Cells

Contractile cells in the heart are connected by intercalated disks, which contain gap junctions that allow for the transmission of force and graded potentials between cells.
They have a stable resting potential.

Action Potential

Autorhythmic cells undergo cyclical depolarization, which is due to the opening of If channels, followed by the closing of If channels and the opening of Ca2+ channels, and finally the closing of Ca2+ channels and the opening of K+ channels.
Contractile cells have a long-lasting action potential, which is due to the opening of Na+ channels, followed by the closure of Na+ channels and the opening of Ca2+ channels, and finally the closing of Ca2+ channels and the opening of K+ channels.
The long refractory period in contractile cells prevents summation of force.

Regulation of Heart Rate

The autonomic nervous system controls heart rate.
Parasympathetic stimulation reduces heart rate by increasing permeability to K+, which hyperpolarizes the cell membrane.
Sympathetic stimulation increases heart rate by increasing permeability to Na+, which depolarizes the cell membrane.

Electrical Conduction System

The electrical conduction system of the heart ensures that contraction is coordinated.
The sequence is: SA node, AV node, bundle of His, Purkinje fibers.

Cardiac Output

Cardiac output is the volume of blood pumped by the heart per minute.
It is calculated by multiplying Stroke volume by Heart rate.
Stroke volume is the volume of blood ejected by the ventricle per beat.

Frank-Starling Mechanism

The Frank-Starling mechanism is an intrinsic control of stroke volume.
It describes the relationship between stroke volume and end-diastolic volume. The greater the end-diastolic volume, the greater the stroke volume.

Extrinsic Control of Stroke Volume

The sympathetic nervous system modulates stroke volume.
Sympathetic stimulation increases stroke volume through the release of norepinephrine.
Norepinephrine increases Ca2+ release from the sarcoplasmic reticulum, leading to stronger contractions.

Cardiac Muscle Contraction

Calcium ions (Ca2+) play a crucial role in initiating and regulating muscle contraction in cardiac muscle cells.
When Ca2+ binds to troponin, it triggers a conformational change that exposes the myosin-binding sites on actin.
This allows for the formation of cross-bridges between actin and myosin, leading to muscle contraction.
During relaxation, Ca2+ unbinds from troponin, allowing the myosin-binding sites on actin to be covered again.

Cardiac Muscle Cells

Cardiac muscle cells are connected through intercalated disks, which contain gap junctions that facilitate the spread of electrical signals and mechanical force between cells.
This allows for synchronized contraction of the heart muscle, ensuring efficient pumping action.
Cardiac muscle cells have a longer action potential duration compared to skeletal muscle cells.
This extended depolarization prevents summation of force, ensuring proper relaxation and refilling of the heart chambers.

Autorhythmic Cells

Autorhythmic cells are specialized cells in the heart that generate their own electrical impulses, setting the pace of the heart.
These cells are located in specific regions of the heart: the SA node, the AV node, and the Purkinje fibers.
The SA node, the fastest of these autorhythmic cells, typically sets the heart's pace.

Electrocardiogram (ECG)

The ECG is a non-invasive tool used to record the electrical activity of the heart.
It provides information about heart rate, rhythm, conduction blocks, and overall coordination of heart contractions.
The ECG can help identify pathologies such as tachycardia, fibrillation, and conduction blocks.

Heart Rate

Heart rate, the number of heartbeats per minute, is regulated by the autonomic nervous system.
Sympathetic stimulation increases heart rate by increasing the rate of spontaneous depolarization in autorhythmic cells.
Parasympathetic stimulation decreases heart rate by reducing the rate of spontaneous depolarization in autorhythmic cells.

Stroke Volume

Stroke volume is the amount of blood ejected from the heart with each beat.
It is modulated by the sympathetic branch of the autonomic nervous system and influenced by the Frank-Starling mechanism.
The Frank-Starling mechanism states that the heart contracts more forcefully when it is stretched or filled with more blood.
Increased sympathetic activity can increase stroke volume by increasing the contractility of the heart muscle.

Control of Cardiac Output

Cardiac output, the amount of blood pumped by the heart per minute, is determined by the product of stroke volume and heart rate (CO = SV x HR).
Cardiac output can be regulated extrinsically by the autonomic nervous system and intrinsically by the Frank-Starling mechanism.
The sympathetic branch of the autonomic nervous system can increase both heart rate and stroke volume, thus increasing cardiac output.
The Frank-Starling mechanism provides a feedback loop, ensuring that the heart pumps out the amount of blood that enters it.

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Description

This quiz covers the essential concepts of heart physiology, including the roles of autorhythmic and contractile cells, the significance of the electrocardiogram (ECG), and the mechanisms of action potential. Test your understanding of how these components contribute to the heart's rhythm and contraction.