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Lecture 19

PHGY 210- Lecture 19- Dr. Guevara.docx

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PHGY 210
Ann Wechsler

thLecture Nineteen Monday February 15 2010The ventricular and atrial cells rest at a negative voltage 90 mVThis is because at this time the membrane is only permeable to potassium If the cell had only K channels it would rest at the Nernst potential the resting potential of K 100 mV This causes K to move into the cell because it is negative against its concentradient gradient Thus the potential lies near to eK cell permeable only to potassium The fast inward sodium current is carried by the fast inward sodium channel A channel is a string of amino acids Sodium channels bring graph up and potassium channels bring the graph down review notes from phgy 1nerves do not memorize IK1 IKS etcSinus Node Action Potentials A sinus node cell is never at restpacemaker cells unlike atrial and ventricular cells therefore they do not have a resting potential Voltage slowly depolarizing is called the pacemaker potential It occurs in the resting part of the heart diastole in which the voltage depolarizes spontaneous diastolic depolarization There is no sodium current in the sinus cells you would think you dont have an upstroke in the action potentials but you have calcium channels still influx of calcium causes depolarization of the membrane and you get the upstroke of the action potential Therefore Icauses the upstroke in sinus cells and I causes the Ca Naupstroke in atrial and centricular cells There is a current called the pacemaker currentmade by hyperpolarizing the cell Called I ffunny I channel is equally permable to Na and KffFast and Slow Action Potentials see picture in slides All action potentials in the heart are categorized as either one of the twoHow quick is the upstroke How fast is the speed of Conductiondetermines fast or slow sinus node cells slow atrioventricular node slow Evereywhere else is fast ventricular muscle atrial muscle bundle of His Purkinje fibresSlope of curve in voltssecondssee picture in slides When does atrial action potential occur During the P wave When do the atrial cells repolarize During the QRS complex Atrial cells have a shorter action potential duration than ventricular cellsCardiac Arrhythmias
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