Cardiac Physiology

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Properties of Cardiac Muscle

-Striated -contraction occurs using same sliding filament mechanism. -cardiac are diff b/c they are short, fat, branched + interconnected -Cardiac muscle fibers have only 1-2 nuclei. More mitochondria.

Properties of Cardiac Muscle II

Desmosomes - hold cells together + prevent separation during contraction Gap Junctions - Allow for AP to pass freely from cell to cell so whole heart contracts instead of a few cells -all cells in heart are coupled electrically by gap junctions

Cardiac Action Potential

1% cardiac muscle = authorhymic -> start own depolarizations which leads to dp of rest of the Heart (pacemaker cells) -Cardiac muscle = all or none effect -abs refractory period of card. musc. longer - almost as long as contraction.

Cardiac Muscle Contraction

90%- contractile - resp. for pumping heart 10-20% Ca need for contraction enters extracellular space. Depolarization -> Na channels opened Slow Ca opened ->influx of Ca K+ enters = repolarization * READ NOTES

Excitation + Electrical Events: Intrinsic Conduction System of Heart

- heart does not depend on nervous system to depolarize/contract. inbuilt mechanism = intrinsic cardiac conduction system. Pacemake cells→self excitory + initiate/distribute impulses.

Cardiac Conduction System

Sinoatrial Node→R atrium where superior vena cava enters. Internodal Pathways→direct pathway from SA node to AV - no gap junctions. AV Node→ fibrous septum btwn R atrium + R vent. Purkinje Fibres→branch off AV bundle

Cardiac Conduction System II STEP 1

Activation of an AP in the SA node first Time = 0

Cardiac Conduction System II STEP 2

Transmitted into the atrial myosites -Reaches AV Node Time = 50 sec

Cardiac Conduction System II STEP 3

100-second delay @ AV Node. Atrial Contraction begins. Time = 150 sec

Cardiac Conduction System II STEP 4

Impulse travels along the interventricular septum within AV bundle. Bundle branches into Purkinje Fibres via moderater band to papillary muscles of R ventricle time = 175 sec

Cardiac Conduction System II STEP 5

Impulse distributed by Purkinje fibres. relayed thruout ventricular myocardium. Atrial contraction completed. Vent. contraction begins time = 225 seconds

Cardiac Conduction System III

No gap junctions between cardiomyocites of atria/ventricles. Av Bundle - only electrical connection btwn atria/ventricles. Branches into 2 paths -connects to purkinje fibres - rapid conduction b/c large fibres + large gap junctions Defects = arrhymias

Electrocardiography

-diagnostic tests records electrical activity in heart by placing electrodes on body P-wave-dp of atria, QRS complex-dp of ventricle+rp of atria at same time, T-wave-small rp of ventricle

Electrocardiography II

P-R Interval = time it takes for impulse to travel from SA>AV thru penetrating fibres down AV bundle Purkinje fibres O-T Interval - time it takes for ventricle to contract + relax again