Anatomy & Physiology II Notes on Cardiovascular
Anatomy & Physiology II Notes on Cardiovascular BIOL 2510 - 001
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This 9 page Class Notes was uploaded by Matthew Vickers on Monday August 29, 2016. The Class Notes belongs to BIOL 2510 - 001 at Auburn University taught by Dr. Shobnom Ferdous in Spring 2016. Since its upload, it has received 17 views. For similar materials see Human Anatomy & Physiology II in Anatomy at Auburn University.
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Date Created: 08/29/16
Cardiac muscle: microscopic anatomy Skeletal muscle o Multinucleate o Long/cylindrical o Lack junctions Cardiac muscle o Uninucleate o Fat/branched fibers • Intercalated discs –contains desmosomes & gap junctions o Desmosomes keep cells together when contracting o Gap junction let ions pass between cells to transmit electrical signal across the entire muscle • Myofibrils with thin (Actin) and thick (Myosin) filaments arranged in sarcomeres • Ttubules(INVAGINATION OF SARCOMERE ) at Z discs , (not at every Aband, I band junction as in skeletal muscle) • SR lacks terminal cisternae(SO NO TRIAD) • 2 types of cells Contractile cells Muscle fibers responsible for heart pumping Make up 99% of cardiac cells Autorhythmic cells Selfexcitable cells that generate their own action potentials (APs) • DEPOLARIZE SPONTANEOUSLY (don’t need AP from neuron to initiate AP) • APS in autorhythmic cells initiate ap in contractile cells o 1% of all cardiac cells Electrical events of the heart • Heart depolarizes and contracts without nervous system stimulation, although rhythm can be altered by autonomic nervous system Lo Na+ Hi Na+ Hi K+ Lo K+ Lo Ca++ Hi Ca++ Lo Cl- Hi Cl- Setting the basic Rhythm: The intrinsic Conduction system • Coordinated heartbeat is a function of: o Presence of gap junctions o Intrinsic cardiac conduction system Network of noncontractile (autorhythmic) cells Initiate and distribute impulses to coordinate depolarization and contraction of heart Coordination heartbeat is a function of?-question will be on test Peacemaker Potential • Action potential initiation by pacemaker cells • Cardiac pacemaker cells have unstable resting membrane potentials called pacemaker potentials or prepotentials • Three parts of action potential o Pacemaker potential K channels are closed, but slow Na channels are open, causing interior to become more positive 2+ o Depo2+rization Ca channels open (around 40 mV), allowing huge influx of Ca , leading to rising phase of action potential + + o Repolarization K channels open, allowing efflux of K , and cell becomes more negative Peacemaker potential & AP of autorhythmic cells Action Threshold potential 2 2 3 No stable resting potential 1 Pacemaker 1 potential • Unlike cardiac contractile fibers & skeletal muscle fibers autorhythmic cells have unstable resting potential, continuously depolarizes (membrane potential never a flat line) • Slow Na+ channels open, K+ channels close g slow depolarization (pacemaker potential) • After reaching threshold: Ca++ channels open g rapid depolarization (starts action potential) • Repolarization: K+ channels open, Ca++ channels close g efflux of K+ AP of contractile cells • Depolarization: Fast voltagegated Na+ channels open g influx of Na+ • Plateau Slow voltagegated Ca++ channels open + few K+ channels open + Na+ channels close g influx of Ca++ (leads to contraction of the muscle) • Repolarization: K+ channels open, Ca++ channels close g efflux of K+ Lo Na+ Hi Na+ Hi K+ Lo K+ Lo Ca++ Hi Ca++ Lo Cl- Hi Cl- Setting the Basic Rhythm: The Intrinsic Conduction System • Sequence of excitation o Cardiac pacemaker cells pass impulses, in following order, across heart in 0.22 seconds Sinoatrial node Atrioventricular node Atrioventricular bundle Right and left bundle branches Subendocardial conducting network (Purkinje fibers) Intrinsic Cardiac Conduction System • Sinoatrial (SA) node (pacemaker) – begins excitation • Atrioventricular node – AV node delay to allow both atria to contract then sends signal on to ventricles • Bundle of HIS –: at superior part of interventricular septum. Atria & ventricles not connected by gap junction. Need Bundle of HIS to conduct impulses from atria to ventricles divides into left/right branches in interventricular septum. Propagates signal to apex • Purkinje Fibers – penetrate heart apex & wind superiorly to base Electrocardiography • Electrocardiograph can detect electrical currents generated by heart • Electrocardiogram (ECG or EKG) is a graphic recording of electrical activity o Composite of all action potentials at given time; not a tracing of a single AP o Electrodes are placed at various points on body to measure voltage differences 12 lead ECG is most typical Electrocardiogram • Electrodes attached to surface of body to detect APs being transmitted through the heart • ECG uses electrodes on body to measure action potentials of heart (displays electrical events of heart not mechanical) • This is not the tracing of a single AP, but the combined AP’s of all nodal/contractile cells at a given time • Displays electrical events, not mechanical events • Terms: o Depolarization: electrical event that leads to systole o Repolarization: electrical event that leads to diastole o Systole: mechanical event of contraction o Diastole: mechanical event of relaxation • Electrical events always come first and cause the Mechanical events • For example: atrial depolarization leads to atrial systole Electrocardiography • Main features: o P wave: depolarization of SA node and atria o QRS complex: ventricular depolarization and atrial repolarization o T wave: ventricular repolarization o PR interval: beginning of atrial excitation to beginning of ventricular excitation o ST segment: entire ventricular myocardium depolarized o QT interval: beginning of ventricular depolarization through ventricular repolarization QRS complex Ventricular depolarization Sinoatrial node Atrial depolarization Ventricular repolarization Atrioventricular P T node ST Segment PR Interval QT Interval 1 0.2 0.4 0.6 0.8 Need to be able to label this for test Electrocardiogram 1) P wave: SA node causes atrial depolarization 2) Delay at AV node, allowing the atria to complete contraction 3) QRS complex: Ventricular depolarization begins a) atrial repolarization hidden Depolarization Repolarization 4) ST segment: Ventricular depolarization is complete 5) T wave: Ventricular repolarization 6) Ventricular repolarization is complete Heart Rate • Normal = 65100 bpm (avg. 72) • Tachycardia = > 100 bpm • Bradycardia = < 60 bpm • ECG = DIAGNOSE HEART PROBLEMS • Arrhythmias uncoordinated atrial & ventricular contractions • SA nodal block – missing Pwave • AV node becomes pacemaker • AV nodal block – blockage of APs through Bundle of His • Increases time between Pwave and QRS st nd rd • 1 , 2 , and 3 degree heart block (Pwave disassociated with QRS) • Ventricular fibrillation (vfib) • Rapid, uncoordinated ventricular contraction, due to heart attack, electrical shock • Results in severe decrease in blood delivery to lungs and tissues Heart murmurs • Abnormal heart sounds • Caused by obstruction: (usually Valves) stenotic valve = fails to open completely o prolapse valve = fails to close completely
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