Cardiac Muscle and Heart Function Quiz

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Questions and Answers

What is the primary function of the myocardium in the heart?

To provide the pumping power of the heart (correct)

To house the coronary arteries and nerves

To protect the heart from external impacts

To facilitate the smooth flow of blood

Which layer of the heart is responsible for providing a smooth surface that directs blood flow?

Epicardium

Myocardium

Pericardium

Endocardium (correct)

What structure is unique to cardiac muscle cells that aids in electrical communication?

Intercalated discs (correct)

Cisternae

T tubules

Sarcoplasmic reticulum

Which of the following correctly describes cardiomyocytes?

They are short, branched, and interconnected Signup and view all the answers

What advantage does the DIAD structure provide to cardiac muscle cells?

It integrates electrical and mechanical events of the muscle cell Signup and view all the answers

Which component of the intercalated discs provides mechanical strength to cardiac muscle cells?

Desmosomes Signup and view all the answers

What type of muscle cell structure does cardiac muscle share with skeletal muscle?

Striated structure Signup and view all the answers

Which component serves as the calcium-storing part in the DIAD structure of cardiac muscle cells?

Terminal cisterna Signup and view all the answers

What is the primary function of the myocardium?

It serves as the heart muscle responsible for contraction. Signup and view all the answers

What role do intercalated discs play among cardiomyocytes?

They facilitate the rapid transmission of electrical signals. Signup and view all the answers

Which structure separates the atrial syncytium from the ventricular syncytium?

Annulus fibrosus Signup and view all the answers

What is the firing frequency of the AV node?

40-60 beats per minute Signup and view all the answers

How does the heart's electrical conduction system initiate contraction?

The SA node generates electrical impulses that spread to the atria. Signup and view all the answers

Which component of the heart conduction system has the slowest conduction speed?

AV node Signup and view all the answers

What type of muscle tissue does the myocardium resemble, and how does it function?

Striated muscle; involuntarily Signup and view all the answers

What is the primary rhythm generated by the SA node called?

Sinus rhythm Signup and view all the answers

What occurs during the isovolumic relaxation stage?

The AV valves and semilunar valves are closed. Signup and view all the answers

Which stage includes atrial contraction forcing blood into the ventricles?

Inflow: Ventricular filling with Atrial systole Signup and view all the answers

What defines tachycardia?

Heart rate above 100 bpm Signup and view all the answers

During which phase of the cardiac cycle do the semilunar valves open?

Ejection: Ventricular ejection Signup and view all the answers

What typically happens to heart rate during sleep?

It can be around 40-50 bpm. Signup and view all the answers

What is true about bradycardia?

It is a heart rate below 60 bpm at rest. Signup and view all the answers

What happens to both systolic and diastolic durations when the heart rate increases?

They both shorten. Signup and view all the answers

Which valves are closed during isovolumic contraction?

Both AV and semilunar valves Signup and view all the answers

What effect does an increase in heart rate have on ventricular filling?

Ventricular filling decreases Signup and view all the answers

What is the formula for calculating cardiac output (CO)?

CO = SV × HR Signup and view all the answers

What sound is associated with the closure of the atrioventricular valves?

S1, the first heart sound Signup and view all the answers

Which artery provides blood supply to the front and a significant part of the septum of the left ventricle?

Left Anterior Descending Artery Signup and view all the answers

What change occurs to stroke volume when heart rate increases?

Stroke volume decreases Signup and view all the answers

What is the resting membrane potential of cardiomyocytes during phase 4 of the cardiac action potential?

Approximately –90 mV Signup and view all the answers

Which phase of the cardiac cycle is associated with the sound commonly referred to as 'lub'?

Ventricular systole Signup and view all the answers

What is the primary function of the coronary arteries?

To supply the myocardium with oxygen and nutrients Signup and view all the answers

What happens to the pressure in the foot veins of a person who stands motionless for 30 seconds?

It increases to +90 mmHg Signup and view all the answers

What is the primary function of the valves in the veins?

To prevent blood from returning to the extremities Signup and view all the answers

Which factor contributes to the development of varicose veins?

Increased foot vein pressure Signup and view all the answers

What is the venous pump, and how does it function?

Muscle contractions that compress veins and push blood toward the heart Signup and view all the answers

Which of the following systems is involved in long-term blood pressure regulation?

Renin-angiotensin-aldosterone system Signup and view all the answers

What occurs during Phase 0 of the action potential in cardiomyocytes?

Sodium channels open leading to rapid depolarization. Signup and view all the answers

During which phase do calcium channels open in cardiomyocytes?

Phase 2 Signup and view all the answers

What is the primary role of the plateau phase in the cardiac action potential?

To allow the cardiac muscle sufficient time to contract effectively. Signup and view all the answers

What characterizes the resting membrane potential of SA node cells compared to normal cardiomyocyte cells?

It is closer to the threshold potential. Signup and view all the answers

What is the main function of the funny Na+ leak channels in SA node cells?

They allow spontaneous depolarization towards the threshold. Signup and view all the answers

Which statement about veins is correct?

Veins are also known as capacitance vessels. Signup and view all the answers

What is the threshold potential value's importance regarding cells?

Cells closer to threshold can be stimulated more readily to generate action potentials. Signup and view all the answers

Which phase immediately follows the plateau phase in cardiomyocytes?

Phase 3 Signup and view all the answers

Study Notes

Cardiac Muscle

Located in the middle layer of the heart, the myocardium
Situated between the endocardium (inner layer) and the epicardium (outer layer)
Muscle cells are called cardiomyocytes
Cardiomyocytes are short, branched, and interconnected
Interconnected via intercalated discs, facilitating electrical and mechanical communication

Cell Structure

Cardiomyocytes are short, branched, and interconnected
Connected by intercalated discs
These discs provide electrical communication and mechanical connection between cells

Cardiac Muscle Layers

Epicardium: The outermost layer of the heart, acting as a protective barrier and a passageway for coronary arteries and nerves
Composed of thin connective tissue and mesothelium
Myocardium: The middle and thickest layer; the main muscle layer responsible for pumping blood
Contains striated muscle cells (cardiomyocytes) connected by intercalated disks
Endocardium: The innermost layer; lines the heart chambers and valves, facilitating smooth blood flow
Composed of thin connective tissue and endothelial cells

Cardiac Muscle Contraction Mechanism

Contraction begins with Ca2+ ions entering the cell (calcium-induced calcium release).
Intercalated discs transmit the action potential from the T tubule to the sarcoplasmic reticulum.
This stimulates calcium release from the sarcoplasmic reticulum.
Calcium released activates actin-myosin filaments, thereby initiating contraction.
Cardiac muscle exhibits less regular and slower contraction dynamics compared to skeletal muscle, due to the difference in structure (DIAD vs. triad).

Cardiac Anatomy

The heart is located in the middle mediastinum, at the level of thoracic vertebrae 15-18.
It has four chambers (two atria and two ventricles)
Right and left sides are separated by the interatrial and interventricular septa.
The interventricular septum is thicker than the interatrial septum to generate more pressure during ventricular contraction.
The right atrium receives blood from the superior and inferior vena cava.

Heart Valves

Heart valves are one-way valves that allow blood flow in a single direction.
Atrioventricular (AV) valves (tricuspid and bicuspid/mitral) control blood flow between atria and ventricles.
Semilunar valves (aortic and pulmonary) control blood flow from the ventricles to the aorta and pulmonary arteries
Their opening and closing depend passively on pressure gradients.

Heart Wall

Three layers: endocardium, myocardium, and epicardium
Myocardium is the heart muscle composed of cardiomyocytes with intercalated discs, facilitating rapid signal transmission.
The rapid spread of this signal across the heart without damping is called a syncytium.

Heart Syncytia

Two functional syncytia in the heart: atrial and ventricular
Separated by a non-conductive fibrous tissue called the annulus fibrosus
This separation allows the atria to contract before the ventricles

Heart Pacemaker Cells

Sinoatrial (SA) node is the primary pacemaker (60-100 bpm) located near the entrance of the superior vena cava in the right atrium.
Atrioventricular (AV) node is the secondary pacemaker (40-60 bpm) located in the interatrial septum behind the tricuspid valve.

Blood Pressure Regulation

Maintaining blood pressure requires both short-term and long-term mechanisms.
Short-term mechanisms involve neural control (e.g., baroreceptor reflex) adjusting blood vessel diameter (vasoconstriction/vasodilation).
Long-term mechanisms involving hormonal pathways (e.g., Renin-angiotensin-aldosterone system) regulate blood volume and electrolyte balance.

Cardiac Output

Cardiac output is the volume of blood pumped by the heart per minute (CO = SV x HR).
Stroke Volume (SV): Volume of blood pumped per heartbeat.
Heart Rate (HR): Number of heartbeats per minute.
Normal resting adult human heart rate is 60-100 bpm.

Cardiac Action Potential

Action potentials in cardiac cells have unique phases.
Phase 4 is the resting potential (-90mV); only K+ channels are open
Phase 0 is rapid depolarization caused by Na+ influx
Phase 1 is early repolarization from K+ efflux
Phase 2 is the plateau phase caused by Ca2+ influx and K+ efflux
Phase 3 is repolarization from continued K+ efflux

SA Node Pacemaker Potential

SA node cells are specialized cardiomyocytes with a resting membrane potential (-60 to -55mV).
This is closer to the threshold potential, making them more excitable compared to other cardiomyocytes.

Funny Channels

Funny channels (Na+ leak channels) in the SA node membrane contribute to maintaining a less negative resting membrane potential.
They facilitate spontaneous depolarization, allowing the SA node to initiate the heart beat.

Venous Circulation

Veins act as capacitance vessels, storing blood.
Venous return is driven by the low pressure gradient towards the heart.
Veins have valves to prevent backflow and skeletal muscle pumps aid venous return.
Factors such as posture (standing) can affect venous pressure, leading to venous pooling or varicose veins.

Coronary Circulation

Coronary arteries supply oxygen and nutrients to the myocardium.
The left coronary artery (LCA) branches into the left anterior descending (LAD) and circumflex arteries, supplying the left side of the heart.
The right coronary artery (RCA) supplies the right side of the heart.

Abnormal Heart Rates

Tachycardia: Heart rate above 100 bpm.
Bradycardia: Heart rate below 60 bpm.
Arrhythmia: Irregular heart beat patterns.

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Description

Test your knowledge on the structure and function of cardiac muscle, specifically focusing on the myocardium and electrical conduction system of the heart. This quiz covers essential components such as cardiomyocytes, intercalated discs, and the unique features of cardiac muscle. Dive in to understand how the heart works at a cellular level!