II. Anatomy: Images

  1. Cardiac Conduction
    1. cvHeartXsEkgGrayBB501.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    2. heartElectrical.jpg
    3. ekg.png
  2. Cardiac Cycle (Wiggers Diagram)
    1. cvCardiacCycleWiggers.png

III. Physiology: Nerve Impulse Transmission

  1. Nerve Impulse (Action Potential)
    1. See Nerve Impulse
    2. As with Neurons, specialized cardiac Muscle transmits electrical signals
      1. nerveActionPotential.png
    3. Vagus Nerve, SA Node and AV Node signals are relatively rapid (similar to Neurons)
      1. Prominent Voltage-Gated Sodium channel mediated depolarization
    4. Atrial Muscle, and especially Purkinje Fibers and Ventricular Muscle tend to have sustained impulses
      1. Prominent Voltage-Gated Calcium channel mediated depolarization
      2. Sustained impulse results in stronger atrial and ventricular contraction
      3. Also results in delayed repolarization (refractory period) protecting against rapid Heart Rates
  2. Sinoatrial Node (SA Node)
    1. Cluster of cells located at the junction of the superior vena cava and the right atrium
    2. The SA Node cell spontaneously generate an electrical signal, depolarizing in adults at 60-100/min
      1. SA Node assumes the Pacemaker function of the heart due to its intrinsic faster rate
      2. Other cardiac tissue also generate spontaneous signals, but at slower rates
    3. Electrical signals pass into the right and left atrial Muscles resulting in atrial contraction
      1. Atrial Muscle depolarization is detected on Electrocardiogram as P Wave
      2. Electrocardiogram does not detect the SA Node firing or atrial repolarization
    4. Signals then continue into the AV Node
    5. The SA Node is perfused by the right Coronary Artery in 50% (remainder by left circumflex artery)
  3. Atrioventricular Node (AV Node)
    1. Small cluster of specialized cardiac Muscle Cells in the interatrial septum near the coronary sinus
    2. AV Node slows electrical conduction, long enough to allow for ventricular filling after atrial contraction
    3. The AV Node depolarizes spontaneously at 40-60/min if the SA Node signal is absent
    4. Gives rise to the Atrioventricular Bundle which passes the electrical signal from the atria to the ventricles
    5. The AV Node is perfused by the right Coronary Artery in 90% (remainder by left circumflex artery)
  4. Purkinje Fibers
    1. Band of specialized cardiac Muscle fibers efficiently and rapidly transmit electrical signals to ventricles
    2. Atrioventricular Bundle (including the left and right bundles) are composed of Purkinje Fibers
  5. Atrioventricular Bundle (AV Bundle, Bundle of His, Kent-His Bundle, Atrioventricular Fasciculus)
    1. Purkinje Fibers transmit electrical signals from the AV Node to the Ventricles
    2. Electrical signals via the Atrioventricular Bundle resulting in Ventricular Contraction (systole)
    3. The ventricular Muscle depolarizes spontaneously at 20-40/min if the SA Node and AV Node signals are absent
    4. Atrioventricular Bundle divides into the left bundle (left ventricle) and right bundle (right ventricle)
      1. Rapid transmission of signals along the Purkinje Fibers ensures simultaneous ventricular contraction

IV. Physiology: Autonomic System Mediators

  1. See Regulation of Circulation
  2. Sympathetic Nervous System (increases Cardiac Output)
    1. Norepinephrine acts at cardiac cells beta-1 Adrenergic Receptors
    2. Increases myocardial contractility
      1. Increases Calcium influx with each Action Potential (resulting in stronger contraction)
    3. Increases Heart Rate
      1. Increases SA Node firing and Action Potential conduction velocity (via Sodium, Calcium influx)
    4. Positive Mediators
      1. Alpha 1 Adrenergic Receptor Agonists
        1. Vasoconstriction and increased cardiac contractility
        2. Examples: Phenylephrine, Norepinephrine, Epinephrine
      2. Alpha 2 Adrenergic Receptor ANTAGONISTS
      3. Beta 1 Adrenergic Receptor Agonists
        1. Increases myocardial contractility (inotrope) and Heart Rate (chronotrope)
        2. Examples: Norepinephrine, Epinephrine
      4. Beta 2 Adrenergic Receptor Agonists
        1. Vasodilation and bronchodilation
        2. Examples: Albuterol
    5. Negative Mediators
      1. Alpha 1 Adrenergic Receptor Antagonists
        1. Alpha Adrenergic Antagonist (e.g. Prazosin, Terazosin, Doxazosin)
        2. Antihypertensives that reduce Peripheral Vascular Resistance
      2. Alpha 2 Adrenergic Receptor AGONISTS
        1. Alpha Adrenergic Central Agonist (e.g. Clonidine, Methyldopa, Aldomet, Guanabenz, Wytensin)
        2. Antihypertensives that reduce Peripheral Vascular Resistance (also reduce contractility, Heart Rate)
      3. Beta 1 Adrenergic Receptor Antagonists
        1. Selective Beta Blockers (e.g. Metoprolol, Bisoprolol, Atenolol)
        2. Decrease Heart Rate and cardiac contractility (as well as Cardiac Output)
        3. Slows AV Node conduction, suppresses SA Node rates, ectopic atrial foci
        4. Inhibit renin release from renal juxtaglomerular cells (hence lowering Blood Pressure)
        5. Decreases cardiac workload and therefore cardiac oxygen demand (Antianginal effect)
      4. Beta 2 Adrenergic Receptor Antagonists
        1. Adverse effect of non-selective Beta Blockers (e.g. Propranolol) resulting in bronchospasm, vasospasm
      5. Peripheral Acting Adrenergic Antagonist
        1. Block Norepinephrine release from postganglionic nerve terminals
        2. Examples: Reserpine, Guanethidine, Guanadrel
  3. Parasympathetic Nervous System (decreases Heart Rate)
    1. Decreases Heart Rate
      1. Vagal Nerve released acetylcholine acts at SA Node, AV Node and Atrial Muscle
        1. Acetylcholine increases SA Node permeability of Potassium
        2. Membrane resting potential hyperpolarized and less susceptible to depolarization
      2. Decreases SA Node firing and Heart Rate
      3. Decreases AV Node Action Potential conduction velocity
      4. Decreases Atrial Muscle Contractility
    2. Marginal effect on reducing myocardial contractility
      1. Sympathetic effect on contractility is dominant

V. Physiology: Other Mediators

  1. Sodium-Potassium Pump Inhibitors
    1. sodiumPotassiumATPase.jpg
    2. Digoxin (Digitalis) is a Sodium-Potassium ATPase Inhibitor
    3. Agents that decrease Sodium-Potassium pump (Sodium efflux from cell) increase intracellular Sodium
      1. Delays AV Node conduction and prolongs AV Node refractory period
      2. Blunts Atrial Tachycardias
    4. Extracellular Calcium may exchange with intracellular Sodium to increase intracellular Calcium
      1. Increased intracellular Calcium increases myocardial contraction strength
  2. Calcium Channel Blockers
    1. Decrease Calcium influx into cell
    2. Dihydropiridine Calcium Channel Blockers (e.g. Nifedipine) primarily target peripheral vessels
      1. Vasodilates by reducing vascular smooth Muscle Contraction
    3. Non-Dihydropiridine Calcium Channel Blockers (e.g. Diltiazem) target both cardiac tissues and vessels
      1. Vasodilation as with Dihydropyridines
      2. Decreased cardiac contractility
      3. Slows Heart Rate by delaying SA and AV Node repolarization

VI. References

  1. Goldberg (2014) Clinical Physiology, Medmaster, Miami, p. 35-50
  2. Guyton and Hall (2006) Medical Physiology, Elsevier Saunders, Philadelphia, p. 103-30

Images: Related links to external sites (from Bing)

Related Studies

Ontology: Structure of atrioventricular node (C0004247)

Definition (FMA) Subdivision of conducting system of heart which is located in the muscular part of the interatrial septum that is continuous with the atrioventricular bundle.
Definition (NCI) A small mass of specialized cardiac muscle fibers, located near the ostium of the coronary sinus and giving rise to the atrioventricular bundle of the conduction system of the heart.
Definition (MSH) A small nodular mass of specialized muscle fibers located in the interatrial septum near the opening of the coronary sinus. It gives rise to the atrioventricular bundle of the conduction system of the heart.
Definition (CSP) small nodular mass of specialized muscle fibers located in the interatrial septum near the opening of the coronary sinus.
Concepts Body Part, Organ, or Organ Component (T023)
MSH D001283
SnomedCT 25943004
English A V Node, A-V Node, A-V Nodes, Atrio Ventricular Node, Atrio-Ventricular Node, Atrio-Ventricular Nodes, Atrioventricular Node, Atrioventricular Nodes, AV Node, AV Nodes, Node, A-V, Node, Atrio-Ventricular, Node, Atrioventricular, Node, AV, Nodes, A-V, Nodes, Atrio-Ventricular, Nodes, Atrioventricular, Nodes, AV, atrioventricular node, AVN - Atrioventricular node, Atrioventricular nodal muscle tissue, Node of Tawara, Nodus atrioventricularis, AV node, AV nodal muscle tissue, Aschoff-Tawara node, AV - Atrioventricular node, tawara node, atrio ventricular node, atrioventricular (AV) node, Atrioventricular node, Structure of atrioventricular node (body structure), Structure of atrioventricular node
French Noeud AV, Noeud d'Aschoff-Tawara, Noeud auriculoventriculaire, Noeud atrio-ventriculaire, Noeud atrioventriculaire, Noeud auriculo-ventriculaire, Noeud septal d'Aschoff et Tawara
Swedish Atrioventrikulär knuta
Czech nodus atrioventricularis
Spanish Nodo Atrioventricular, Nodo Auriculoventricular, Nudo Auriculoventricular, Nodo AV, Nódulo Atrioventricular, Nódulo Auriculoventricular, Nudo Atrioventricular, Nudo AV, estructura del nódulo auriculoventricular (estructura corporal), estructura del nódulo auriculoventricular, nodo AV, nódulo auriculoventricular, Nódulo AV
Finnish Eteis-kammiosolmuke
Italian Nodo atrio-ventricolare, Nodo A-V, Nodo AV, Nodo atrioventricolare
Russian ATRIOVENTRIKULIARNYI UZEL, ASHOFA-TAVARY UZEL, PREDSERDNO-ZHELUDOCHKOVYI UZEL, АТРИОВЕНТРИКУЛЯРНЫЙ УЗЕЛ, АШОФА-ТАВАРЫ УЗЕЛ, ПРЕДСЕРДНО-ЖЕЛУДОЧКОВЫЙ УЗЕЛ
Latvian AV mezgls, Atrioventrikulārais mezgls
Polish Węzeł przedsionkowo-komorowy
Japanese Ashoff-田原結節, 房室結節, AVノード, アショッフ-田原結節, 田原の結節, 田原結節
Croatian ATRIOVENTRIKULARNI ČVOR, AV ČVOR, ATRIOVENTRIKULSKI ČVOR
Norwegian Atrioventrikulærknute, AV-knute, Nodus atrioventricularis
Portuguese Nodo AV, Nó AV, Nodo Atrioventricular, Nódulo Atrioventricular, Nó Auriculoventricular, Nodo Auriculoventricular, Nódulo Auriculoventricular, Nó Atrioventricular, Nódulo AV
German AV-Knoten, Aschoff-Tawara-Knoten, Atrioventrikularknoten
Dutch AV-knoop, Atrioventriculaire knoop, Knoop, atrioventriculaire, Nodus atrioventricularis

Ontology: Bundle of His (C0006382)

Definition (FMA) Subdivision of conducting system of heart which consists of the atrial part and the ventricular part of the atrioventricular bundle and is the direct continuation of the atrioventricular node.
Definition (MSH) Small band of specialized CARDIAC MUSCLE fibers that originates in the ATRIOVENTRICULAR NODE and extends into the membranous part of the interventricular septum. The bundle of His, consisting of the left and the right bundle branches, conducts the electrical impulses to the HEART VENTRICLES in generation of MYOCARDIAL CONTRACTION.
Definition (NCI) A bundle of specialized heart muscle fibers that conducts impulses from the atrioventricular node to the ventricles.
Concepts Body Part, Organ, or Organ Component (T023)
MSH D002036
SnomedCT 345000
English Atrioventricular Bundle, Atrioventricular Bundles, Bundle, Atrioventricular, Bundles, Atrioventricular, His Bundle, bundle of His, Penetr atrioventricular bundle, Atrioventricular bundle muscle tissue, Fasciculus atrioventricularis, Atrioventricular fasciculus, Kent-His Bundle, Bundle, Kent-His, Kent His Bundle, atrioventricular bundle, bundle his, bundle of his, his bundle, His bundle, Atrioventricular bundle, Penetrating atrioventricular bundle, Atrioventricular bundle structure (body structure), Atrioventricular bundle structure, Atrioventricular bundle, NOS, Bundle of His, A-V Bundle
Swedish His bunt
Czech Hisův svazek, Kentův-Hisův svazek
Spanish Fascículo Atrioventricular, Haz Auriculoventricular, Rama Derecha del Fascículo Atrioventricular, Tronco Atrioventricular, Haz de His, Tronco Auriculoventricular, Fascículo Auriculoventricular, estructura del haz auriculoventricular (estructura corporal), estructura del haz auriculoventricular, haz auriculoventricular penetrante, haz auriculoventricular, haz de His, Haz Atrioventricular
Finnish Hisin kimppu
German Truncus fasciculi atrioventricularis, Atrioventrikularbündel, His-Bündel
Russian PUCHOK GISA, ATRIOVENTRIKULIARNYI PUCHOK, АТРИОВЕНТРИКУЛЯРНЫЙ ПУЧОК, ПУЧОК ГИСА
Japanese His束, ヒス束, 房室束, 房室索
Italian Fascio atrioventricolare, Fascio di His
Polish Pęczek Hisa, Pień pęczka przedsionkowo-komorowego
Croatian HISOV SNOP, ATRIOVENTRIKULSKI SNOP
Norwegian Atrioventrikulærbunten, His-Tawaras bunt, AV-bunten, His’ bunt, Truncus fasciculi atrioventricularis
Portuguese Feixe de His, Fascículo Atrioventricular, Feixe Atrioventricular
Dutch Atrioventriculaire bundel, Bundel van His, Fasciculus atrioventricularis, His, bundel van
French Faisceau atrio-ventriculaire, Faisceau atrioventriculaire, Faisceau de His

Ontology: Cardiac conduction system (C0018796)

Definition (FMA) Conducting tissue of heart which consists of specialized cardiac myocyte in the myocardium.
Definition (MSH) An impulse-conducting system composed of modified cardiac muscle, having the power of spontaneous rhythmicity and conduction more highly developed than the rest of the heart.
Definition (MSHCZE) Impulsní převodní systém sestávající z přizpůsobené srdeční svaloviny, která umožňuje spontánní rytmičnost a více vyvinutou schopnost vodivosti impulsů než zbytek srdce. R
Definition (CSP) impulse conducting system composed of modified cardiac muscle and having the power of spontaneous rhythmicity and conduction more highly developed than the rest of the heart.
Concepts Body System (T022)
MSH D006329
SnomedCT 24964005
English Conduction System, Heart, Conduction Systems, Heart, Heart Conduction System, Heart Conduction Systems, System, Heart Conduction, Systems, Heart Conduction, heart conduction system, Cardiac conduct system structr, Systema conducens cordis, Conducting system of heart, Systema conducente cordis, Complexus stimulans cordis, Cardionector, conduction heart system, conducting system of heart, cardiac conduction system, conducting heart system, Heart conduction system, Cardiac conducting system structure, Cardiac conducting system structure (body structure), Cardiac conduction system, NOS, Cardiac conduction system
Swedish Retledningssystemet
Czech srdce - převodní systém
Finnish Sydämen johtoratajärjestelmä
Russian SERDTSA PROVODIASHCHAIA SISTEMA, СЕРДЦА ПРОВОДЯЩАЯ СИСТЕМА
Japanese ケント束, Kent束, 心臓刺激伝導系
Croatian SRCE, PROVODNI SUSTAV
Latvian Not Translated[Heart Conduction System]
Polish Układ przewodzący serca
Norwegian Hjertets ledningssystem
Spanish Sistema Conductor del Corazón, Sistema de Conducción del Corazón, estructura del sistema de conducción cardíaco (estructura corporal), estructura del sistema de conducción cardíaco, sistema de conducción cardíaco, sistema de conducción del corazón, Sistema de Conducción Cardíaco
Portuguese Sistema de Condução do Coração, Sistema Condutor do Coração, Sistema de Condução Cardíaco
German Herzreizleitungssystem
Italian Sistema di conduzione del cuore
Dutch Geleidingssysteem van het hart
French Système cardio-necteur, Système cardionecteur, Système de conduction du coeur, Tissu nodal

Ontology: Structure of purkinje fibers (C0034144)

Definition (FMA) Conducting tissue of heart which consists of Purkinje myocytes.
Definition (MSH) Modified cardiac muscle fibers composing the terminal portion of the heart conduction system.
Definition (CSP) modified cardiac muscle fibers composing the terminal portion of the heart conduction system; do not confuse with Purkinje cells in the cerebellum.
Concepts Tissue (T024)
MSH D011690
SnomedCT 13050003
English Fibers, Purkinje, Purkinje Fibers, heart Purkinje's fiber, Ventricular conduction fibers, Ventricular conduction fibres, Purkinje system (heart), Subendocardial branches of atrioventricular bundle, Purkinje fiber, Set of subendocardial branches of atrioventricular bundle, Myofibra conducens cardiacus, Rami subendocardiales fasciculi atrioventricularis, purkinje fibers, purkinje fibres, purkinje fiber, Purkinje fibers, Purkinje fibres, Structure of purkinje fibers (body structure), Structure of purkinje fibres, Structure of purkinje fibers, Purkinje Fiber, Purkinje's fiber (heart)
Swedish Purkinjetrådar
Czech Purkyňova vlákna
Finnish Purkinjen syyt
Russian PURKIN'E VOLOKNA, MIOTSIT SERDECHNYI PROVODIASHCHII, МИОЦИТ СЕРДЕЧНЫЙ ПРОВОДЯЩИЙ, ПУРКИНЬЕ ВОЛОКНА
Croatian PURKINJEOVA VLAKNA
Spanish Ramos Subendocárdicos, Fibras de Purkinje, estructura de las fibras de Purkinje (estructura corporal), estructura de las fibras de Purkinje, fibras de Purkinje
Portuguese Ramos Subendocárdicos, Miócito Condutor Cardíaco, Fibras de Purkinje
Polish Włókna Purkinjego
Norwegian Purkinje-fibre
German Purkinje-Fasern
Italian Fibre di Purkinje
Dutch Purkinje vezels, Purkinjevezel, Vezel, Purkinje-
French Fibres de Purkinje, Réseau de Purkinje

Ontology: Sinoatrial Node (C0037189)

Definition (FMA) Subdivision of conducting system of heart at the junction of the right atrium and the superior vena cava, around the sinoatrial nodal branch of right coronary artery and is continuous with the internodal tract.
Definition (NCI) A cluster of specialized cells located in the upper area of the right atrium. These cells generate the electrical impulses that result in the normal sinus rhythm.
Definition (MSH) The small mass of modified cardiac muscle fibers located at the junction of the superior vena cava (VENA CAVA, SUPERIOR) and right atrium. Contraction impulses probably start in this node, spread over the atrium (HEART ATRIUM) and are then transmitted by the atrioventricular bundle (BUNDLE OF HIS) to the ventricle (HEART VENTRICLE).
Concepts Body Part, Organ, or Organ Component (T023)
MSH D012849
SnomedCT 88210001
English Node, Sino-Atrial, Node, Sinoatrial, Nodes, Sino-Atrial, Nodes, Sinoatrial, Sino Atrial Node, Sino-Atrial Node, Sino-Atrial Nodes, Sinoatrial Node, Sinoatrial Nodes, Node of Keith and Flack, SN - Sinus node, Nodus sinuatrialis, Cardiac pacemaker, SA node, Sinus node of Keith and Flack, Node of Keith-Flack, SA nodal muscle tissue, Sinuatrial node, Sinu-atrial node, Koch's node, Sinuatrial nodal muscle tissue, SA - Sinoatrial node, cardiac pacemaker, sinus node, node sa, sa node, sinu atrial node, sinoatrial node, pacemaker cardiac, sino-atrial node, sinuatrial node, node sinoatrial, node sinus, Node, Sinu-Atrial, Node, Sinuatrial, Nodes, Sinu-Atrial, Nodes, Sinuatrial, Sinu Atrial Node, Sinu-Atrial Node, Sinu-Atrial Nodes, Sinuatrial Node, Sinuatrial Nodes, Sinus node, Sinoatrial node, Structure of sinoatrial node (body structure), Structure of sinoatrial node, S-A Node, Node, Sinus, Sinus Nodes, Sinus Node, Nodes, Sinus
French Noeud sinoatrial, Noeud sino-auriculaire, Noeud sinu-atrial, Noeud sinuatrial, Noeud sinusal, Noeud sinoauriculaire, Noeud de Keith et Flack, Noeud sino-atrial
Swedish Sinusknuta
Czech nodus sinoatrialis, sinoatriální uzel
Spanish Nodo Sinusal, Nodo Sinoatrial, Nódulo Sinusal, Nodo Sino-atrial, Nodo Sinoauricular, Nódulo Sinoatrial, estructura del nódulo sinusal (estructura corporal), estructura del nódulo sinusal, nodo sinoauricular, nódulo de Keith y Flack, nódulo sinusal, Nódulo Sinuatrial
Finnish Sinussolmuke
Russian KISA-FLEKA UZEL, SINUSNO-PREDSERDNYI UZEL, SINUSNYI UZEL, КИСА-ФЛЕКА УЗЕЛ, СИНУСНО-ПРЕДСЕРДНЫЙ УЗЕЛ, СИНУСНЫЙ УЗЕЛ
Italian Nodo seno atriale, Nodo seno-atriale, Nodo del seno, Nodo senoatriale
Polish Węzeł zatokowo-przedsionkowy
Japanese Keith結節, 洞結節, キース-フラック結節, 洞房結節
Norwegian Nodus sinoatrialis, Sinusknute
Portuguese Nodo Sinoatrial, Nodo Sinuatrial, Nódulo Sinoatrial, Nodo Sinusal, Nódulo Sinuatrial, Nódulo Sinusal, Nó Sinoatrial, Nó Sinuatrial, Nó Sinusal
German Sinoatrialknoten, Nodus sinuatrialis, Sinuatrialknoten, Sinusknoten
Dutch Knoop van Keith-Flack, Knoop, sinus-, Sinusknoop, Nodus sinuatrialis