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Phys2 Lect 3
Question | Answer |
---|---|
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 |