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29 Cards in this Set
- Front
- Back
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What causes the delay of conduction in the atrioventricular node
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fewer gap junction which create a greater resistance and small diameter fibers
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location of the bundle of his
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superior aspect of the intervnetricular septum
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what part of the conductive system pierces the fibrous skeleton and descends along the inter ventricular septum
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the bundle of his or the AV Bundle
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what divides into right and left bundle branches
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the bundle of his or the av bundle
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attributes of the AV Bundle
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it is one way AP conduction (no re entry)
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what penetrates and depolorize the inner 1/3 of the ventricular myocardium
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the right and left bundle branches
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fiber branches propagate the AP throughout the ventricular myocardium
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ventricular perkinje fibers
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why is AP conduction so fast in the ventricular purkinje fibers
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very large fibers and highly permeable gap junctions
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this conducts the AP efficiently insuring synchronous ventricular myocardial contraction
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purkinje fibers
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why does the faster discharge rate occurs in the SA node
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because the resting potential is more positive
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pacemaker potential
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spontaneous depolarizations produced by opening of slow na/ca channels
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it is primarily what into SA nodal cells that generate pacemaker potentials
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sodium
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sodium inflow changes the membrane potential from −60 to
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-40 at this time minimal K outflow occurs
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When pacemaker potential reaches the threshold potential of −40 mV what happens
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voltage gated calcium channels in the sarcolemma open allowing entry of additional extracellular calcium into nodal cells
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where may abnormal ectopic pacemakers arise
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the av node (junction), penetrating AV bundle, purkinje fibers and within atrial or ventricular myocardium
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What is stokes-adams syndrome
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a sudden av bundle block causes the heart to stop beating for about 5-20 sec (asystole)
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what are the signs and symptoms of stokes adams syndrome
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the patient faints, aps ar generated from purkinje fibers at a rate of 15-40bpm, death may occur is asystolic interval is too long
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what do refractory periods do
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allow for efficiet rhythmic myocardial contractions
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absolute refractory period
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the time eriod during the AP when the myocardial cells cannot be stimulated by another AP
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relative refractory period
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the time period during the AP when myocardial cells can be stimulated by another AP, howerver, a greater electrical stimulus is required to cause contraction
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how much blood volume within the atria passively flow into the ventricles prior to atrial contraction
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about 80%
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what is a A wave caused by
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left atrial contraction
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What is a C wave caused by
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left ventricular contraction
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when the left ventricle contracts what goes on with the mitral valve
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mitral valve leaflets bow bulge backward into the left atrium transiently increasing atrial pressure
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what is v wave (pressure ramp) caused by
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slow blood flow from the pulmonary veins into the left atrium during ventricular contraction(while the mitral valve is closed)
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3 events occur during ventricular filling during diastole
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period of rapid filling, diastasis, and atrial systole (atrial kick)
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what happens in the period of rapid filing
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occurs when the mitral valve initially opens and most ventricular fill occurs during this time. 80% of left atrial volume passively flows into the left ventricle
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what happens in diastasis
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small blood volume flowing from the pulmonary veins in to the left atrium passively flows into the left ventricle through an open mitral valve
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what happens during atrial systole
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atrial kick. the remaining 20% of the blood volume is actively ejected i to t the left ventricle during atrial contraction
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