Cardiac Muscle Physiology Overview

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Questions and Answers

What happens at 0mV in terms of ion channels during repolarization?

Ca++ channels open and K+ channels close

Na+ channels close and K+ channels open

Ca++ channels close and K+ channels open (correct)

Na+ channels open and K+ channels close

What prevents premature contractions in the heart?

Plateau phase

High levels of troponin

Long refractory period (correct)

Activation of Ca++ channels

Which node would fire the fastest without endocrine control?

Purkinje fibers

Atrioventricular bundle

AV node

SA node (correct)

Which component of the heart's conduction system has the lowest firing rate?

Purkinje fibers Signup and view all the answers

What is the purpose of an electrocardiogram (ECG)?

To record electrical signals of the heart Signup and view all the answers

Where is the heart located in the body?

Between the lungs in the mediastinum Signup and view all the answers

Which blood vessels attach at the base of the heart?

Superior and inferior vena cava Signup and view all the answers

What is the function of ventricles in the heart?

Pump blood out to the body or lungs Signup and view all the answers

What is unique about the pulmonary vein among all arteries?

It carries oxygenated blood Signup and view all the answers

Which layer of the heart produces fluid that lubricates the pericardial cavity?

Visceral layer Signup and view all the answers

What do auricles in the heart do?

Hold blood and empty into atria Signup and view all the answers

What does the P wave represent in the cardiac cycle?

Depolarization of the atria Signup and view all the answers

Which phase of the cardiac cycle is associated with 'atrial kick'?

Atrial systole Signup and view all the answers

What is the main function of an artificial pacemaker in the heart?

Delivers electrical impulses to ensure effective heart contractions Signup and view all the answers

In the cardiac cycle, what occurs during ventricular diastole?

Relaxation (T wave), semilunar valves close and atrioventricular valves are closed too Signup and view all the answers

What is the amount of blood pushed out by the ventricles called?

Stroke volume Signup and view all the answers

Which statement is true about the T wave in the cardiac cycle?

Signifies relaxation of the heart chambers Signup and view all the answers

What is the main function of the endothelium in the heart?

To release endothelins which regulate growth patterns of cardiac muscle cells Signup and view all the answers

Which structure divides the heart into chambers?

Septum Signup and view all the answers

What is the main role of the atrioventricular valves in the heart?

Separate atria from ventricles Signup and view all the answers

Which chamber receives oxygenated blood from the pulmonary veins?

Left atrium Signup and view all the answers

What is the function of the moderator band in the heart?

Conduct cardiac impulses Signup and view all the answers

What is the significance of valves in the heart?

Ensure bidirectional blood flow Signup and view all the answers

What is the primary role of coronary circulation in the heart?

Allow blood flow even with a partial blockage Signup and view all the answers

What is the function of autorhythmicity in cardiac muscle cells?

Initiate and propagate action potential through the heart Signup and view all the answers

What is the main function of Purkinje fibers in the heart?

To spread electrical impulses around the ventricles Signup and view all the answers

What is the normal range for cardiac output (CO) in a healthy individual?

4 - 8 L/min Signup and view all the answers

Which of the following statements about heart murmurs is correct?

Heart murmurs are caused by turbulent blood flow. Signup and view all the answers

What is the formula for calculating Stroke Volume (SV) in relation to End-Diastolic Volume (EDV) and End-Systolic Volume (ESV)?

$SV = EDV - ESV$ Signup and view all the answers

Which factor can decrease heart rate according to the text?

Hypothermia (low body temperature) Signup and view all the answers

What is the role of norepinephrine in heart function according to the text?

Shortens the repolarization period Signup and view all the answers

Which reflex is triggered by increased blood in the atria according to the text?

Atrial reflex Signup and view all the answers

What does S2 correspond to in heart sounds?

Opening of semilunar valves Signup and view all the answers

Study Notes

Heart Anatomy

The heart is a muscle that pumps 5.25 L of fluid per minute.
Located between the lungs in a space called the mediastinum.
Separated from other structures by the pericardium, a tough membrane.
The base of the heart is superior and medial to the apex.

Heart Structure

4 chambers in the heart: 2 atria and 2 ventricles.
Atria are superior, collect blood, and push it into lower chambers.
Ventricles are inferior and pump blood out to the body or lungs.
2 circuits: pulmonary and systemic.
Right ventricle connects to the pulmonary trunk and left ventricle connects to the aorta.

Heart Membranes and Layers

2 layers: fibrous and serous pericardium.
Serous layer has 2 sublayers: parietal and visceral layers separated by pericardial cavity.
Cavity filled with lubricating fluid.
Visceral layer is called epicardium and produces fluid.

Heart Features

2 auricles: thin-walled structures that can hold blood and empty into atria.
Sulci: fat-filled grooves that contain coronary blood vessels.

Layers of the Heart

Epicardium: most superficial layer.
Myocardium: middle, thickest layer, muscle cells, nerve fibers, and blood vessels.
Endocardium: innermost layer, lines the chambers filled with blood, covers heart valves.
Endothelium: cells that line the blood vessels, release endothelins, which are strong vasoconstrictors.

Internal Structures

Septum: divides the heart into chambers, physical extensions of myocardium, 3 septa in the heart.
Fossa ovalis: a depression in the interatrial septum, was a foramen ovale (opening) while a fetus.
Atrioventricular valves: separate atria from ventricles, tricuspid on right and mitral or bicuspid on left.
Semilunar valves: separate ventricles from blood vessels, pulmonary and aortic valves.

Chambers of the Heart

Right atrium: receives deoxygenated blood from systemic circulation, contains pectinate muscles.
Right ventricle: receives deoxygenated blood from the right atrium, has chordae tendineae connected to 3 papillary muscles.
Left atrium: receives oxygenated blood from the pulmonary veins, no pectinate muscles.
Left ventricle: thicker muscle, receives oxygenated blood from the left atrium, pushes blood into the aorta.

Valves of the Heart

Ensure unidirectional blood flow.
Semilunar valves have no muscular attachments, but make an audible sound as they close.
Tricuspid and mitral valves close due to papillary muscles.
Valve disorders are usually caused by inflammation.

Coronary Circulation

Cyclical and not continuous.
Arteries branch off the aorta just superior to the semilunar valve.
Coronary arteries bring blood to the myocardium and other components.
Anastomosis: blood vessel interconnections to allow blood to flow even if there is a partial blockage in another branch.

Cardiac Muscle and Electrical Activity

Autorhythmicity: cardiac muscle can initiate an electrical potential at a fixed rate.
Myocardial conducting cells: initiate and propagate the action potential through the heart.
Myocardial contractile cells: conduct impulses and contract to pump blood through the body.

Comparative Conduction

SA node sets normal cardiac rhythm, known as the pacemaker.
AV node receives impulse from SA node and slows it down.
Bundle of His receives impulse from AV node and flows down the interventricular septum.
Purkinje fibers spread the impulse around the ventricles.

Membrane Potentials

Cardiac conductive cells have Na+ channels that allow a slow influx to create the spontaneous depolarization.
Cardiac contractile cells depolarize as an impulse reaches them, then they plateau before repolarizing.

Calcium Ions

Allow for the plateau phase in cardiac contractile cells.
Bind to troponin to allow the myosin and actin cross-bridge.

Electrocardiogram (ECG)

Records electrical signals of the heart.
3, 5, or 12 leads.
P wave: depolarization of the atria.
QRS complex: depolarization of ventricles and it masks the repolarization of the atria.
T wave: repolarization of ventricles.

Cardiac Cycle

Begins at atrial contraction and ends with ventricular relaxation.
Systole: pumping blood into circulation.
Diastole: chambers are relaxed and filling with blood.

Phases of the Cardiac Cycle

Atrial systole: atria contract from superior portion following depolarization (P wave).
Atrial diastole: muscles relax as ventricles begin to contract.
Ventricular systole: blood in ventricles is the end-diastolic volume (EDV) or preload.
Ventricular diastole: relaxation, semilunar valves close, and atrioventricular valves are closed too.

Heart Sounds

Healthy heart has 2 audible sounds: S1 and S2 (lub dub).
S1: closing of atrioventricular valves.
S2: closing of semilunar valves.

Murmur

Caused by turbulent blood flow.
Inhalation increases blood flow to the right side and may increase the amplitude of a right-sided murmur.
Expiration partially restricts blood flow to the left side and may increase the amplitude of a left-sided murmur.

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Description

Test your knowledge on the physiological processes of the cardiac muscle, including repolarization, refractory period, ion channels, and conduction pathways. Learn about the role of calcium ions, action potentials, SA node firing, and the function of troponin in muscle contraction.