cardiac properties action potentials i. rhythmicity ii. excitability
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/1.jpg)
CARDIAC PROPERTIESACTION POTENTIALS
I. RHYTHMICITYII. EXCITABILITY
LECTURE – 2 DR. ZAHOOR ALI SHAIKH
1
![Page 2: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/2.jpg)
I. RHYTHMICITY
What is Rhythmicity?• Action Potential in SA-Node is called Auto Rhythmicity or self excitability.• It is also called Pace-maker potential.
2
![Page 3: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/3.jpg)
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
3
![Page 4: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/4.jpg)
Cause of Prepotential
• Na+ going inside• Ca++ going inside• ↓ K+ going outside• After Prepotential we get Depolarization and
RepolarizationCause of Depolarization - Ca++ going insideCause of Repolarization - K+ going outside
4
![Page 5: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/5.jpg)
Phase 4
Phase 0 Phase 3
5
![Page 6: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/6.jpg)
S A NODE POTENTIAL
6
PHASE 4 = Prepotential
PHASE 0 =Depolarization
PHASE 3 =Repolarization
![Page 7: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/7.jpg)
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.
7
![Page 8: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/8.jpg)
Effect 0f Sympathetic and parasympathetic Stimulation on Prepotential (Pace Maker Potential)
8
![Page 9: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/9.jpg)
SA NODAL POTENTIAL & CHANGES
9
![Page 10: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/10.jpg)
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
10
![Page 11: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/11.jpg)
Effect 0f Sympathetic Stimulation on Prepotential
Why Sympathetic Stimulation causesPrepotential 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.
11
![Page 12: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/12.jpg)
Effect 0f parasympathetic Stimulation on Prepotential
Why parasympathetic causes Prepotential tooccur 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.
12
![Page 13: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/13.jpg)
Action Potential in Ventricular Muscle
Fiber13
II.EXCITIBILITY
![Page 14: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/14.jpg)
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 14
![Page 15: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/15.jpg)
EXCITABILITY
15
•Ventricular Muscle membrane has resting membrane potential of -90mV.•Action Potential of ventricular muscle fiber has four phases 0, 1, 2, 3 ,4.
![Page 16: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/16.jpg)
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)
16
![Page 17: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/17.jpg)
ACTION POTENTIAL IN VENTRICULAR MUSCLE FIBER & REFRACTORY
PERIODS
17
![Page 18: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/18.jpg)
• AP in Ventricular Muscle Fiber and Refractory Periods
• AP followed by contraction
18
![Page 19: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/19.jpg)
REFRACTORY PERIODAbsolute 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.
19
![Page 20: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/20.jpg)
REFRACTORY PERIODS
Relative Refractory PeriodRelative Refractory Period occurs after ARP.
During Relative Refractory Period, second action potential can be triggered by very strong stimulus.
20
![Page 21: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/21.jpg)
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].
21
![Page 22: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/22.jpg)
Action Potential & Contractile Response In Cardiac
Muscle
22
![Page 23: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/23.jpg)
Difference between Myocardial AP & Pacemaker
Potential
23
![Page 24: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/24.jpg)
Difference between Myocardial AP & Pacemaker Potential
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
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
24
![Page 25: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/25.jpg)
ACTION POTENTIAL OF DIFFERENT CARDIAC TISSUES
25
![Page 26: CARDIAC PROPERTIES ACTION POTENTIALS I. RHYTHMICITY II. EXCITABILITY](https://reader034.vdocuments.net/reader034/viewer/2022051021/56816802550346895ddd81ef/html5/thumbnails/26.jpg)
THANK YOU
26