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Phys2 Lect 3

What main Ion is the focus of E-C coupling? Ca2+
What types of cardiac cells will experience SLOW respsonse depolarization? SA node. AV node. NO PLATEAU
What types of cardiac cells will experience FAST response depolarization? 1.Atrial. 2.Purkinje. 3.Endocardial. 4.myocardial. 5.Epicardial.
What is responsible for the automaticity of the heart? Phase 4 Slow Diastolic Depolarization.
What ion channels are responsible for the phase 4 slow diastolic depolarization? I(f) channels (Inward "funny" Na+ channels). Open slowly during repolarization, allowing a small gNa to be generated leading to slow depolarization. **Ica,t channels also contribute.
Why is the SA node the pacemaker of the heart instead of he AV node? Because the SA node has the FASTEST rate of depolarization per min (80/min). **AV node is only 50/min
Mechanism behind ANS effects on HR SYMP: NE increases the rate of I(f) channel opening, thus increasing the gNa influx and speeding up phase 4. Parasymp: ACh dec I(f) channels as well as activating I(kACh) channels which will prolong phase 4 slowing down the HR.
What could be the cause behind a Pt presenting with chest pain and HR around 50bpm? MI affecting the SA node, leaving the AV node as the controller.
Conduction speeds excitation extends from SA node to the ventricles? SA node:0.05m/s. Atria:1m/s. AV node:0.01-0.05m/s. Bundle of His/Purkinje fibers:2-5m/s
AV delay between the atrial and ventricular contractions? Is due to the slower conduction speed (0.01-0.05 m/s). **Is dependent on voltage-gated Ca2+ channels I(Ca,L).
What effect with Ca2+-channel blockers have on the heart? Decreases HR by decreasing the conduction thru the AV node.
Why does the conductance of purkinje fibers and bundle of His need to be so much faster? So that the ventricular myocytes contract almost entirely together.
What two ways can myocardium increase its cell-to-cell conduction speed? 1.Cell Diameter: Increasing diameter increases conductance (decreases resistance Ri). 2.Increase the # of tight junctions per cross-sectional area. **Purkinje fibers have both of these making them very fast
Phases of ventricular AP: Phase 4 RESTING: Em maintained at -90mV due to inward rectifier K+ channels.
Phases of ventricular AP: Phase 0 RAPID DEPOLARIZATION: Voltage-gated Na+ channels open and close quickly. **They have the same activation & inactivation gates that neurons do.
Phases of ventricular AP: Phase 1 REPOLARIZATION: voltage-gated K+ channels open. voltage-gated Na+ channels become inactive.
Phases of ventricular AP: Phase 2 PLATEAU: competition b/w the voltage-gated K+ channels and the: 1.Voltage-gated Ca2+ channels (Ica,L). 2.Late Na+ channels. **Lasts up to 80-150ms
Phases of ventricular AP: Phase 3 RAPID REPOLARIZATION: the Ica,L and Late Na+ channels both close, elimating influx and leaving only the K+ efflux.
What prevents Artial re-excitation by ventricular depolarization? ANULUS FIBROSUS
Created by: WeeG



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