Pacermaker cells

Pacermaker cells - Pacermaker cells- self- depolarize and...

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Pacermaker cells- self- depolarize and initiate activation of heart. Purkinje fibers- cells specialized for rapid conduction. Cells in AV node- slow rate of rise and low amplitude slow cell to cell spread of activation. SA node- activation normally originates form pacemaker cells localized here. AV node- site conduction delay in artioventricular activation. Filter atrial arrythmias from ventricles. Contains some pacemaker cells. His Bundle bundle branch system- composed of purkinje fibers. Specialized ventricular conducting system. Distributing network. Vertebrate heart myogenic Initiation activation occurs in muscle cells . Cell to cell spread of activation Neural input can change heart rate, change activation and change force to muscle contraction, but neural input not required. Electrical coupling- among cardiac muscle cells occurs through connexons with intercalated disks. Parameters for Activation of Cardiac tissue 1. Rate of rise and amplitude of the action potential of cells with in a tissue. 2. Electrical coupling among cells- presence and # of low resistance junctions. 3. Geometric relationship among cells with the tissue. 4. Refractory properties of inward, depolarizing current channels.
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1. Affect of inward and outward ionic current flow on the membrane potential referenced to the resting membrane potential (inside the cell negative). 2. For our purposes, current flow represents movement of + charge. Inward ionic current flow depolarizes the cell makes the inside of the cell less negative or more positive. Outward ionic current flow repolarizes the cell makes the inside of the cell less positive or more negative. 3. Depolarization occurs when there is net movement + charge into the cell. 4. Repolarization occurs when there is net movement + put of the cell. Depolarization Repolarization activation of K channels and current flow. Sequence of the heart: SA node Atrial muscle AV Node His bundle bundle branch system ventricular muscle. Cardiac AP not all or none. AP amplitude and rate of rise increases from the beginning to the end of the RRP. Effective and Relative Refractory Periods ERP of tissue – tissue behaves as if its cells are inexcitable. No spread of activation through tissue. Therefore conduction block. RRP for tissue- tissue is excitable. Spread of activation through tissue. However, CV slowed and conduction time prolonged b/c time course for cell to cell spread of activation is prolonged.
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During ERP of a tissue, an AP may or may not be generated in cells w/in the tissue, but the APs are incapable of generating an AP in the adjacent tissue. Therefore, the tissue behaves as if it is in excitable refractory.
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This note was uploaded on 09/23/2010 for the course NPB 8746546 taught by Professor Goldberg during the Spring '10 term at UC Davis.

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Pacermaker cells - Pacermaker cells- self- depolarize and...

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