trevor
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im studyin physio from kaplan and fa. there r a few major differences bw d 2 sources.
purkinje fiber has myosite like or sa node like action potential?
slow diastolic depolarisation of sa nodeis thru- fa says increased na conduct kaplan says decr k conductance
initial rise in cardiac output in exarcise due to -- hr says kaplan.stroke volume says fa
someone plz thro some light. im really confused
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| mildus
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"purkinje fiber has myosite like or sa node like action potential?" Myocyte (I'll check in Ganong)
"slow diastolic depolarisation of sa nodeis thru- fa says increased na conduct kaplan says decr k conductance" ---- I would say that it is decreased K+ conductance. Because K+ wants to go outside thus making transmembrane potential more negative, so in SA node it is more logical to believe that K+ conductance is decreased so K+ stays more in the cell thus making transmembrane potential more positive and nearer to the threshold potential.
"initial rise in cardiac output in exarcise due to -- hr says kaplan.stroke volume says fa " ------ I would say that it depends. One of the possible explanations would be the effect of training. It is considered that sportmen increase their CO primarely by way of increasing stroke volume, and other people increase their CO usually mostly by way of increasing their heart rate. So, it is always both heart rate and stroke volume (sympathetic nervous system influence) that increase the CO but it is only the matter of proportion
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| trevor
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"it is more logical to believe that K+ conductance is decreased so K+ stays more in the cell thus making transmembrane potential more positive and nearer to the threshold potential. "
if going just by logic -increased na conductance woould also bring na inside cell and cause it to depolarise
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| mildus
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That's right, trevor.
Some books even say that in the SA node they are both increased Na+ conductance and decreased K+ conductance which are important for prepotential.
But, in Ganong, it is mentioned only that it is decreased K+ conductance which is the most important for SA node prepotential (pacemaker potential). [Ganong Review of Medical Physiology, 21st edition, 2003, chapter:28, page:550]
And about Purkinje fibers, as I said in previous post, their action potential is more like ventricular muscle fiber action potential. There is a picture in [Ganong Review of Medical Physiology, 21st ed, 2003, chapter28, page 549].
Edited by mildus on 10/03/05 - 10:55 AM. Reason: correction
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| mildus
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Both increased Na conductance and decreased K conductance could result in prepotential, but Ganong only says about K+.
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| mildus
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In Cardiovascular physology concepts by Richard E. Klabunde, 2004 (online edition www.cvphysiology.com) it is also said that Purkinje fiber action potential is similar to that of ventricular muscle fiber. This book also states that in the SA and AV node, a pacemaker potential exists thanks to K+, Na+ and even Ca++.
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| trevor
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thanks mildus
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