Cardiac Muscle Anatomy and Function
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Questions and Answers

Which layer of the heart is primarily responsible for the heart's pumping action?

  • Pericardium
  • Epicardium
  • Endocardium
  • Myocardium (correct)

What is the unique cellular structure that facilitates electrical communication and mechanical connection between cardiomyocytes?

  • Intercalated discs (correct)
  • Sarcomeres
  • T tubules
  • Desmosomes

Which component of the intercalated discs provides mechanical strength and helps cells stay together during contraction?

  • Desmosomes (correct)
  • T tubules
  • Myofilaments
  • Gap junctions

What is the primary role of the endocardium?

<p>To line the heart chambers and valves, ensuring smooth blood flow (C)</p> Signup and view all the answers

What does the 'DIAD' structure in cardiac muscle cells consist of?

<p>One T tubule and one terminal cisterna (C)</p> Signup and view all the answers

What is the outermost layer of the heart called?

<p>Epicardium (A)</p> Signup and view all the answers

What creates the striated appearance of cardiac muscle cells?

<p>The arrangement of actin and myosin filaments (A)</p> Signup and view all the answers

What is the function of the T-tubules in the DIAD structure of cardiac muscle cells?

<p>To transmit electrical impulses (C)</p> Signup and view all the answers

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

<p>It functions as the heart muscle responsible for contractions. (A)</p> Signup and view all the answers

Which structure separates the atrial syncytium from the ventricular syncytium?

<p>Annulus fibrosus (D)</p> Signup and view all the answers

What is the role of pacemaker cells in the heart?

<p>They generate spontaneous electrical impulses. (D)</p> Signup and view all the answers

Which node serves as the primary pacemaker of the heart?

<p>SA node (A)</p> Signup and view all the answers

What is the conduction speed of the AV node?

<p>0.05 m/s (A)</p> Signup and view all the answers

What is the term for the rapid spread of a signal across cardiomyocytes in the heart?

<p>Syncytium (B)</p> Signup and view all the answers

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

<p>To prevent blood from returning away from the heart (A)</p> Signup and view all the answers

How many impulses per minute does the SA node typically produce?

<p>60-80 impulses (A)</p> Signup and view all the answers

What is the function of the His bundle in the heart's electrical conduction system?

<p>To transmit signals from the atria to the ventricles (A)</p> Signup and view all the answers

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

<p>It increases to +90 mmHg (C)</p> Signup and view all the answers

Which system is primarily responsible for long-term regulation of blood pressure?

<p>Renin-angiotensin-aldosterone system (D)</p> Signup and view all the answers

What is one consequence of increased pressure in the capillaries due to standing for long periods?

<p>Fluid leaking into the interstitial space causing leg swelling (B)</p> Signup and view all the answers

What is the result of weakened or damaged vein valves?

<p>Blood accumulation in the veins (A)</p> Signup and view all the answers

What role does DIAD play in cardiac muscle contraction?

<p>It transmits the action potential from the T tubule to the sarcoplasmic reticulum. (B)</p> Signup and view all the answers

How does the contraction mechanism of cardiac muscle differ from that of skeletal muscle?

<p>Cardiac muscle has a less regular and slower contraction dynamics. (A)</p> Signup and view all the answers

Where is the human heart located within the body?

<p>In the middle mediastinum at thoracic vertebrae T5-T8. (C)</p> Signup and view all the answers

Which statement accurately describes the structure of the heart valves?

<p>Atrioventricular valves are found between atria and ventricles. (B)</p> Signup and view all the answers

What is the primary function of the heart's septa?

<p>To separate the left and right sides of the heart. (A)</p> Signup and view all the answers

Which artery branches directly from the aorta in the proper sequence?

<p>Brachiocephalic artery, left carotid artery, left subclavian artery. (B)</p> Signup and view all the answers

What determines the opening and closing of the heart valves?

<p>Pressure gradients in the heart chambers. (D)</p> Signup and view all the answers

What is the composition of the interventricular septum compared to the interatrial septum?

<p>Thicker due to higher pressure generation requirements. (B)</p> Signup and view all the answers

During which stage are the semilunar valves closed?

<p>Isovolumic contraction (A), Isovolumic relaxation (D)</p> Signup and view all the answers

What occurs during the ventricular filling phase?

<p>Atrial contraction forces blood into the ventricles (B)</p> Signup and view all the answers

Which condition indicates a heart rate above 100 bpm at rest?

<p>Tachycardia (B)</p> Signup and view all the answers

What happens to the heart rate during sleep?

<p>Decreases to around 40-50 bpm (B)</p> Signup and view all the answers

Which value indicates bradycardia?

<p>Below 60 bpm (A)</p> Signup and view all the answers

During which stage is blood flow in the ventricles stopped?

<p>Isovolumic relaxation (C), Isovolumic contraction (D)</p> Signup and view all the answers

What characterizes an arrhythmia?

<p>Irregular beating pattern (B)</p> Signup and view all the answers

What is the heart rate range for a normal resting adult human?

<p>60-100 bpm (B)</p> Signup and view all the answers

What happens during Phase 0 of the action potential?

<p>Sodium channels open, allowing Na+ to flow into the cell. (C)</p> Signup and view all the answers

What is the primary role of the plateau phase (Phase 2) in cardiac muscle?

<p>To allow time for the heart muscle to pump blood effectively. (C)</p> Signup and view all the answers

What distinguishes the resting membrane potential of SA node cells from that of normal cardiomyocyte cells?

<p>SA node cells have a resting potential closer to the action potential threshold. (B)</p> Signup and view all the answers

During Phase 3 (repolarization), what occurs in the cell?

<p>Potassium channels open and calcium channels close. (D)</p> Signup and view all the answers

What initiates the spontaneous activity of SA node cells?

<p>The presence of funny leak Na+ channels. (A)</p> Signup and view all the answers

Why are veins referred to as capacitance vessels?

<p>They can store blood due to their ability to contract and relax. (C)</p> Signup and view all the answers

What occurs during Phase 1 (early repolarization)?

<p>Potassium channels open, leading to potassium efflux. (D)</p> Signup and view all the answers

What is the typical resting membrane potential of a normal cardiomyocyte cell?

<p>-90 mV (A)</p> Signup and view all the answers

Flashcards

Myocardium

The middle layer of the heart responsible for pumping blood. It contains cardiomyocytes, the heart muscle cells.

Intercalated Discs

Specialized junctions that connect cardiomyocytes, allowing electrical communication and strong mechanical connections. They are essential for coordinated heart contractions.

Cardiomyocytes

Short, branched cells that make up heart muscle. They have a striated structure due to the arrangement of actin and myosin filaments.

DIAD

A structure formed by the T tubule and terminal cisternae of the sarcoplasmic reticulum in cardiomyocytes. It plays a crucial role in regulating the contraction mechanism by releasing calcium.

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T Tubule

Tubular structures extending from the cell membrane (sarcolemma) deep into the cardiomyocyte. They help propagate electrical signals and ensure synchronized contraction.

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Terminal Cisternae

Calcium storage compartments within the sarcoplasmic reticulum of cardiomyocytes. They release calcium ions triggering muscle contraction.

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Epicardium

The outermost layer of the heart. It protects the heart and serves as a buffer against external impacts. Coronary arteries and nerves pass through this layer.

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Endocardium

The innermost layer of the heart. It lines the heart chambers and valves, ensuring smooth blood flow.

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What is a DIAD?

A specialized structure found in cardiac muscle cells, responsible for transmitting the electrical signal from the T tubule to the sarcoplasmic reticulum, triggering calcium release and initiating contraction.

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What is calcium-induced calcium release?

The process of calcium ions entering the cell, triggering the release of more calcium from the sarcoplasmic reticulum, leading to muscle contraction.

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What is the T tubule?

The thin membrane surrounding the muscle fiber, facilitating the rapid spread of action potential throughout the cell.

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Syncytium

This refers to the coordinated contraction of the entire heart, which is possible due to the interconnected structure of the cardiomyocytes.

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SA (sinoatrial) node

The primary pacemaker of the heart, located near the entrance of the superior vena cava in the right atrium. It generates electrical impulses that control the heart rate.

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What is the sarcoplasmic reticulum?

The internal network of membrane-bound sacs within muscle cells, responsible for storing and releasing calcium ions.

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What is a triad?

A cluster of three interconnected structures in skeletal muscle: a T tubule and two terminal cisternae of the sarcoplasmic reticulum, involved in calcium release for muscle contraction.

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AV (atrioventricular) node

A part of the heart's conduction system, located in the interatrial septum. It slows down the electrical impulse from the SA node, allowing the atria to contract before the ventricles.

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What is the mediastinum?

The central compartment of the thorax, containing the heart and major blood vessels.

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Pacemaker cells

This group of cells responsible for generating electrical impulses in the heart. They are crucial for the conduction system, which controls the heart rate and rhythm.

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His Bundle

The electrical signal travels from the SA node to the AV node, then passes through this bundle to the ventricles, causing them to contract.

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What are atrioventricular valves?

The valves located between the atria and ventricles, preventing backflow of blood.

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Purkinje Fibers

These fibers branch out from the His bundle, distributing the electrical signal throughout the ventricular muscle, ensuring a synchronized contraction.

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What are semilunar valves?

The valves located at the exit points of the aorta and pulmonary trunk, preventing backflow of blood.

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Ventricular Filling

The stage in the cardiac cycle when the ventricles relax and fill with blood. This is considered part of diastole.

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Ventricular Ejection

The stage in the cardiac cycle when the ventricles contract and eject blood. This is considered part of systole.

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Diastole

The stage in the cardiac cycle when the ventricles are relaxed and the heart is refilling with blood. The AV valves are open, allowing blood to flow from the atria into the ventricles.

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Systole

The stage in the cardiac cycle when the ventricles are contracting, expelling blood to the lungs and body. The semilunar valves are open, allowing blood to flow out of the heart.

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Heart Rate

The heart rate at which it can vary according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide.

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Tachycardia

A high heart rate, defined as above 100 bpm at rest.

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Bradycardia

A low heart rate, defined as below 60 bpm at rest.

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Arrhythmia

When the heart is not beating in a regular pattern, this is referred to as an arrhythmia.

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Vein Valves

These are one-way valves located in veins, preventing blood from flowing backward. They ensure blood travels only towards the heart.

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Venous Pump

The mechanism that helps move blood from the legs back to the heart, primarily through the contraction of leg muscles that squeeze veins.

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Varicose Veins

A condition where blood pools in veins, often near the surface of the skin, due to weakened or damaged valves.

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Sympathetic Nervous System

The branch of the autonomic nervous system responsible for the 'fight or flight' response, triggering physiological changes like increased heart rate and blood pressure.

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Parasympathetic Nervous System

The branch of the autonomic nervous system responsible for the 'rest and digest' functions, promoting relaxation and energy conservation.

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Depolarization

A rapid increase in the cell's positive charge, primarily due to the influx of sodium ions (Na+). It marks the beginning of a heart muscle cell's contraction.

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Early Repolarization

A brief period of repolarization where potassium ions (K+) flow out of the cell, slightly reducing the positive charge.

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Plateau Phase

A sustained period where the cell's positive charge remains relatively stable, primarily due to the influx of calcium ions (Ca2+).

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Repolarization

The cell returns to its resting negative charge as potassium ions (K+) flow out, while calcium ions stop entering.

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SA Node

Specialized cells in the heart that initiate the heartbeat, determining the heart's rhythm.

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Funny Channels

Channels in the SA node cell membrane that allow sodium ions (Na+) to leak in, making the cell more likely to generate an action potential.

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Capacitance Vessels

The ability of veins to expand and hold blood.

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Venous Circulation

The collection of veins that carry blood back to the heart.

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Study Notes

Cardiac Muscle

  • Located in the middle layer of the heart (myocardium)
  • Situated between the endocardium (inner layer) and the epicardium (outer layer)
  • Cells are called cardiomyocytes
  • Cardiomyocytes are short, branched, and interconnected
  • Connected by intercalated discs, facilitating electrical and mechanical communication

Cardiac Muscle Cell Structure

  • Cardiomyocytes are short, branched, and interconnected
  • Interconnected via intercalated discs (providing electrical and mechanical connections)

Cardiac Muscle Layers

  • Epicardium: The outermost layer of the heart; protective; contains coronary arteries and nerves
  • Structure: Thin connective tissue and mesothelium
  • Myocardium: The middle, thickest layer; responsible for pumping blood; composed of cardiomyocytes
  • Structure: Striated muscle cells connected by intercalated discs
  • Endocardium: The innermost layer; smooth lining of heart chambers and valves; directs blood flow; composed of thin connective tissue and endothelial cells

Cardiac Muscle Layers - Further Detail

  • Myocardium: The thickest and most important layer, responsible for heart pumping
  • Functions: Cardiac muscle layer that pumps blood
  • Cardiomyocytes: Perform the contraction function; striated muscle cells connected by intercalary discs
  • Structure: Striated muscle cells (cardiomyocytes) connected by intercalated discs

Cardiac Muscle Cells: DIAD

  • The structure found in cardiac muscle cells
  • Integrates electrical and mechanical events in the muscle cell

Cardiac Action Potential Phases

  • Phase 0 (Depolarization): Rapid Na+ influx
  • Phase 1 (Early Repolarization): Brief K+ efflux
  • Phase 2 (Plateau): Persistent Ca2+ influx; balanced by delayed outward K+ efflux
  • Phase 3 (Repolarization): K+ efflux
  • Phase 4 (Resting Potential): Only K+ channels open, membrane potential approximately -90mV

SA Node Pacemaker Potential

  • Specialized cardiomyocytes
  • Resting potential is closer to 0 than in normal cardiomyocytes (-60mV to -55mV)
  • Threshold value for depolarization is lower than normal pacemaker cells
  • Allows for automatic rhythmic depolarization

Funny Channels

  • Na+ leak channels
  • Cause resting membrane potential to be less negative
  • Allows SA node cells to spontaneously generate depolarization
  • Facilitates rhythmic activity without nerve stimulation

Venous Circulation

  • Veins act as capacitance vessels, storing blood
  • Blood from systemic veins collects in the right atrium
  • Veins have low contractility
  • Veins have valves to direct blood toward the heart
  • Foot vein pressure increases during standing (90 mmHg)

Heart Rate

  • Frequency of heart contractions per minute (bpm)
  • Varies based on physical needs
  • Normal resting adult HR: 60-100 bpm

Cardiac Output

  • Volume of blood pumped by the heart per minute
  • Calculated as: Cardiac Output = Stroke Volume x Heart Rate
  • Normal CO in adults: ~5600 mL/min

Heart Sounds

  • S1 (Lub): Closure of AV valves (tricuspid and mitral); beginning of ventricular systole
  • S2 (Dub): Closure of semilunar valves (aortic and pulmonary); end of ventricular systole

Coronary Circulation

  • Branches of arteries supply myocardium with oxygen and nutrients
  • Left Coronary Artery (LCA):
    • Left anterior descending (LAD) artery, supplies front and large part of the septum
    • Circumflex artery, wraps around left side of heart
  • Right Coronary Artery (RCA): Branches from aorta, supplies right atrium, right ventricle and part of septum

Blood Pressure Regulation

  • Short-term: Neural mechanisms (baroreceptors) adjust blood vessel diameter
  • Long-term: Hormonal mechanisms (renin-angiotensin-aldosterone system) regulate blood volume and sodium reabsorption.

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Cardiac Muscle Physiology PDF

Description

Test your knowledge on the anatomy and function of cardiac muscle. This quiz covers various components of the heart, including layers, cellular structures, and unique features of cardiomyocytes. Challenge yourself to understand the vital roles these structures play in maintaining heart function.

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