29 Questions
What is the main characteristic of autorhythmic cells in the heart?
Unstable resting potential that gradually depolarizes
Which cells are autorhythmic and involved in generating electrical impulses in the heart?
Specialized cells like those in the SA and AV nodes
What is the role of autorhythmic cells in coordinating the heart's contractions?
Acting as pacemakers for rhythmic contractions
What happens during depolarization in the action potentials of autorhythmic cells?
Voltage-gated calcium channels open, allowing calcium ions to enter
Which condition can result from abnormalities in the intrinsic conduction system of the heart?
Arrhythmias
What does the pacemaker potential eventually trigger in autorhythmic cells?
Action potential
What percentage of cardiac muscle tissue do autorhythmic cells typically make up?
~1%
What ion primarily leads to depolarization during the action potentials of autorhythmic cells?
Calcium ions
'Unlike contractile cells' is a description that helps distinguish autorhythmic cells by their:
'Unstable resting potential'
'Restoration of the resting membrane potential' primarily involves the movement of which ion during repolarization in autorhythmic cells?
'Potassium ions'
What is the primary function of the sinoatrial (SA) node?
To initiate electrical impulses that trigger cardiac muscle contraction
Which structure is responsible for briefly delaying the electrical signal to allow complete atrial contraction before ventricular contraction?
AV node
Which structure conducts the electrical impulse from the AV node down the interventricular septum?
AV bundle (Bundle of His)
What is the function of the subendocardial conducting network (Purkinje fibers)?
To rapidly distribute the electrical impulse throughout the ventricles, coordinating their contraction
Which part of the brainstem controls sympathetic innervation of the heart, stimulating an increase in heart rate and contractility?
Cardioaccelerator center
What is the primary function of the cardioinhibitory center located in the medulla oblongata?
To regulate parasympathetic innervation of the heart via the vagus nerve, decreasing heart rate and contractility
During which phase of the cardiac action potential do cardiac cells experience a prolonged plateau characterized by the influx of calcium ions and efflux of potassium ions?
Plateau phase
What is the primary function of systole in the cardiac cycle?
To contract and eject blood into the circulation
Which phase of the cardiac cycle immediately follows ventricular ejection?
Isovolumetric ventricular relaxation
In which phase of the cardiac cycle do the atrioventricular valves close and the ventricles contract isometrically without changing volume?
Isovolumetric contraction
Which of the following statements accurately represents the relationship between End Diastolic Volume (EDV) and Stroke Volume (SV)?
SV = EDV - ESV
Which of the following mechanisms is primarily responsible for the parasympathetic control of heart rate?
Release of acetylcholine, increasing potassium permeability and decreasing calcium permeability
If a patient's End Diastolic Volume (EDV) is 120 mL and their End Systolic Volume (ESV) is 50 mL, what is their Stroke Volume (SV)?
70 mL
If a patient's heart rate is 75 beats per minute (bpm) and their Stroke Volume (SV) is 65 mL, what is their Cardiac Output (CO)?
$4.875 \text{ L/min}$
Which of the following statements correctly describes the role of catecholamines in the sympathetic control of heart rate?
Catecholamines bind to 1-adrenergic receptors, increasing sodium and calcium permeability, leading to increased heart rate
If a patient's End Diastolic Volume (EDV) is 140 mL and their Stroke Volume (SV) is 90 mL, what is their End Systolic Volume (ESV)?
50 mL
Which of the following statements accurately describes the relationship between Cardiac Output (CO), Heart Rate (HR), and Stroke Volume (SV)?
CO = HR SV
Which of the following statements accurately describes the role of acetylcholine in the parasympathetic control of heart rate?
Acetylcholine binds to muscarinic receptors, increasing potassium permeability and decreasing calcium permeability, leading to decreased heart rate
If a patient's Cardiac Output (CO) is 5.2 L/min and their Heart Rate (HR) is 65 beats per minute (bpm), what is their Stroke Volume (SV)?
$80 \text{ mL/beat}$
Study Notes
Cardiac Cycle
- The cardiac cycle involves the contraction and relaxation of the heart, consisting of two main phases: systole and diastole.
- Systole is the phase of contraction, during which the heart ejects blood into the circulation.
- Diastole is the phase of relaxation, during which the heart fills with blood.
Heart Rate and Stroke Volume
- Heart rate (HR) is the number of times the heart beats per minute (bpm).
- Stroke volume (SV) is the volume of blood ejected from the heart with each contraction (heartbeat).
- Cardiac output (CO) is the total volume of blood pumped by the heart per unit time, calculated by multiplying heart rate by stroke volume (CO = HR x SV).
End-Diastolic Volume (EDV), End-Systolic Volume (ESV), and Stroke Volume (SV)
- End-diastolic volume (EDV) is the volume of blood in the ventricles at the end of diastole, just before ventricular contraction.
- End-systolic volume (ESV) is the volume of blood remaining in the ventricles at the end of systole, just after ventricular contraction.
- Stroke volume (SV) is the difference between end-diastolic volume (EDV) and end-systolic volume (ESV), representing the volume of blood ejected from the ventricles with each heartbeat (SV = EDV - ESV).
Heart Rate Control Mechanisms
- Parasympathetic control: The parasympathetic nervous system, mediated by acetylcholine, decreases heart rate by increasing potassium channel permeability, leading to hyperpolarization of cardiac cells.
- Sympathetic control: The sympathetic nervous system, activated by catecholamines (norepinephrine and epinephrine), increases heart rate by binding to β1-adrenergic receptors, leading to increased permeability to sodium and calcium ions.
Sequence of Excitation
- The sequence of excitation in the heart involves:
- SA node (sinoatrial node): Initiates electrical impulses that trigger cardiac muscle contraction.
- AV node (atrioventricular node): Delays the electrical signal briefly to allow for complete atrial contraction.
- AV bundle (Bundle of His): Conducts the electrical impulse from the AV node down the interventricular septum.
- Right and left bundle branches: Extend along the septum toward the apex of the heart.
- Subendocardial conducting network (Purkinje fibers): Rapidly distributes the electrical impulse throughout the ventricles, coordinating their contraction.
Extrinsic Innervation of the Heart
- Medulla oblongata: Part of the brainstem, regulates autonomic functions, including heart rate and rhythm.
- Cardioaccelerator center: Within the medulla oblongata, controls sympathetic innervation of the heart, stimulating an increase in heart rate and contractility.
- Cardioinhibitory center: Also located within the medulla oblongata, regulates parasympathetic innervation of the heart, leading to a decrease in heart rate and contractility.
Explore the characteristics and functions of noncontractile cardiac cells within the intrinsic conduction system of the heart. Learn about autorhythmic cells like those in the SA and AV nodes, their role in coordinating heart contractions, and their unique resting potential.
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