1 / 26

CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY

CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY . LECTURE – 2 DR. ZAHOOR ALI SHAIKH. I. RHYTHMICITY. What is Rhythmicity? Action Potential in SA-Node is called Auto Rhythmicity or self excitability. It is also called Pace-maker potential.

varian
Download Presentation

CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CARDIAC PROPERTIESACTION POTENTIALSI. RHYTHMICITYII. EXCITABILITY LECTURE – 2 DR. ZAHOOR ALI SHAIKH

  2. I. RHYTHMICITY What is Rhythmicity? • Action Potential in SA-Node is called Auto Rhythmicity or self excitability. • It is also called Pace-maker potential.

  3. Pacemaker Potential( Rhythemicity ) • SA node is pacemaker of normal heart • SA node has a spontaneous slow depolarization called as pacemaker potential or pre potential • Membrane potential begins at -60mv and slowly depolarizes to -40mv, which is threshold for producing Action Potential

  4. Cause of Prepotential • Na+ going inside • Ca++ going inside • ↓ K+ going outside • After Prepotential we get Depolarization and Repolarization Cause of Depolarization - Ca++ going inside Cause of Repolarization - K+ going outside

  5. Phase 0 Phase 3 Phase 4

  6. S A NODE POTENTIAL PHASE 4 = Prepotential PHASE 0 = Depolarization PHASE 3 = Repolarization

  7. WHY SA-NODE IS PACE-MAKER OF THE HEART? • SA-Node is Pace-maker because - It has pace-maker or Prepotential - It has fastest rate of auto Rhythmicity, 70-80 Action Potential/min, which drives the rest of the heart at this rate. NOTE • SA-Node is specialized cardiac muscle cell, situated in the atrial wall, near the opening of superior vena-cava.

  8. Effect 0f Sympathetic and parasympathetic Stimulation on Prepotential (Pace Maker Potential)

  9. SA NODAL POTENTIAL & CHANGES

  10. Effect 0f Sympathetic and parasympathetic Stimulation on Prepotential (Pace Maker Potential) • Epinephrine & Norepinephrine (Adrenaline and Noradrenaline) causes Prepotential to occur faster therefore increase the heart rate • Acetylcholine causes Prepotential to occur at slow rate therefore decrease the heart rate

  11. Effect 0f Sympathetic Stimulation on Prepotential Why Sympathetic Stimulation causes Prepotential to occur faster? • Because Sympathetic Stimulation causes - more Na+ influx [entry] - more Ca2+ influx [entry] - decreased K+ efflux [going outside] • Therefore, membrane potential changes quickly from -60mV to -40mV [increases the slope of Prepotential] and when it reaches the threshold level, AP starts.

  12. Effect 0f parasympathetic Stimulation on Prepotential Why parasympathetic causes Prepotential to occur after long time? • Because Parasympathetic Stimulation causes - decreased Na+ influx [entry] - decreased Ca2+ influx [entry] - increased K+ efflux [going outside] • Therefore, membrane potential changes slowly from -60mV to -40mV [decreases the slope of Prepotential] and when it reaches the threshold level, AP starts.

  13. Action Potential in Ventricular Muscle Fiber II.EXCITIBILITY

  14. Myocardial Action Potential ( Excitability ) • Once myocardial cells are stimulated by action potential originating in SA node, it produces its own action potential • Action Potential From Ventricular Muscle Fiber

  15. EXCITABILITY • Ventricular Muscle membrane has resting membrane potential of -90mV. • Action Potential of ventricular muscle fiber has four phases 0, 1, 2, 3 ,4.

  16. Action Potential in Myocardial cell • Resting membrane potential is about -90mv • Rapid depolarization (Phase 0) – due to Na+ influx • Rapid Repolarization (Phase 1) - Due to closure of Na+ channels • Slow depolarization (Phase 2) - this is called Plateau phase and is maintained for 200 – 300 ms – due to Ca++ influx • Repolarization (Phase 3) – due to K+ efflux • Resting Membrane Potential (Phase 4)

  17. ACTION POTENTIAL IN VENTRICULAR MUSCLE FIBER & REFRACTORY PERIODS

  18. AP in Ventricular Muscle Fiber and Refractory Periods • AP followed by contraction

  19. REFRACTORY PERIOD Absolute Refractory Period [ARF] • ARF is that period, where second action potential can not be triggered by the stimulus. • ARF last for about 200-250ms and includes depolarization, plateau phase, and half of Repolarization phase.

  20. REFRACTORY PERIODS Relative Refractory Period Relative Refractory Period occurs after ARP. During Relative Refractory Period, second action potential can be triggered by very strong stimulus.

  21. NOTE • Ventricular AP is followed by ventricular contraction. Ventricular contraction occurs during ARP, therefore, ventricular muscle can not be Tetanized [contraction can not be summated].

  22. Action Potential & Contractile Response In Cardiac Muscle

  23. Difference between Myocardial AP & Pacemaker Potential

  24. Difference between Myocardial AP & Pacemaker Potential • Pacemaker Potential • Memb. Potential is about • -60mv • It is unstable • Automatic • Prepotential • Phase 0,3 ,4.(no phase 1 & 2). • slow depolarization due to ca++ influx • Has no plateau phase Myocardial AP • Resting Memb. Potential is about -90mv • It is stable • Needs stimulus • No Prepotential • Phases 0,1,2,3 & 4 • Rapid depolarization due to Na+ influx • Has plateau phase

  25. ACTION POTENTIAL OF DIFFERENT CARDIAC TISSUES

  26. THANK YOU

More Related