Electrical Activity Of The Heart
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Electrical Activity Of The Heart as PDF for free.
More details
- Words: 698
- Pages: 29
Chapter III
Rhythmical excitation of the heart 1. Electrical activity of the heart 2. Electrophysiological properties 3. Electrocardiogram (ECG)
1.Electrical activity of the heart
1) Resting membrane potential 2) Action potential
Types of cardiac cell Working cells Atrial myocytes Ventricular myocetes Conducting cells SAN AVN His bundles Purkinje fibers
Recall: Outward current o positive ion efflux or negative ion influx o Bring membrane potential to hyperpolarized state
Inward current o Positive ion influx or negative ion efflux o Bring membrane potential to depolarization state
Ion Concentration Ion
Extracellular Intracellular
E
(mmol)
(mmol)
(mV)
K+
4
135
-94
Ca2+
2
0.0001
+132
Cl-
104
9
-65
Na+
145
10
+70
1)Resting membrane potential Equilibrium potential: At rest, the cardiac muscle membrane is highly permeable to K+ and almost impermeable to the others. The contractile cell’s resting potential is about – 90mV.
2)Action potential
a. Contractile cell
b. autorhythmic cell
a. Contractile cells: Phase 0
deploarization, upstroke From –90 mV to +30 mV Duration 1–2ms, APA ~120mV, Speed of depolarization 800-1000V/s
Phase 1 Early rapid repolarization MP from +30 mV to 0 mV Duration ~10ms Spike shape
Phase 2
Plateau, slow repolarization MP is ± 0mV Duration 100150ms Determine ADP
Phase 3
Terminal repolarization Late repolarization MP from 0 mV to –90 mV Duration 100-150ms
Phase 4
Resting state MP -90mV
Ionic Mechanisms Underlying the Action Potential
Phase 0 Voltage-gated sodium channel open
Phase 1 Phase 1 (fast repolarization phase 1) Sodium channel inactivated Transient outward current activated. Carried by potassium
Phase 2
Phase 2 (plateau phase) MP stayed at ± 0 mV resulting in a plateau Inward component: Ca2+ Outward component:
K+ efflux (Ik ） +
Ca2+ influx(ICa
， L
）
Phase 3 Phase 3 (Repolarization) Ca2+ channel closed K+ channels are activated Rapid K+ efflux resulting in repolarization bringing membrane potential to its resting
Phase 4
MP tends to a stable state Na+/K+ pump is activated Ca2+ pump is activated
summary
Depolarization is very rapid & is due to the inward diffusion of sodium (0). Repolarization begins with a slow outward diffusion of potassium, but that is largely offset by the slow inward diffusion of calcium (1 & 2). So, repolarization begins with a plateau phase. Then, potassium diffuses out much more rapidly as the calcium channels close (3), and the membrane potential quickly reaches the 'resting' potential (4), which is due to the Na+K+- pump.
b. Autorhythmic cells(sinus node) Autorhythmic cells exhibit PACEMAKER potentials.
The key to the rhythmical firing of pacemaker cells is that, these cells will slowly depolarize by themselves.
Phase 4
There are several kind of currents that contribute to spontaneously depolarization at phase 4 in pace-maker cells of SAN. An outward flow or "leak" of K+ ions, declining with the time goes on. An inward flow of Ca2+ . This relatively slow depolarization continues until the threshold potential is reached ( -40 mV ~ -50mV.
Phase 0 The SA node do not have fast sodium channels. The depolarisation in phase 0 is mainly caused by a slow influx of Ca2+ ions via voltage-gated Ca2+ channels, that opened when the threshold was reached.
Phase 3 The Ca2+ channels are inactivated, soon after they opened. Repolarization starts when the K+ channels open, allowing efflux of K+ that renders the interior of the cell negative.
summary Depolarization is due to the slow calcium channels open (0). Repolarization
is due to the outward diffusion
of potassium (3). During
phase 4 there is a progressive reduction
in outward current of K+ and a steady inward current of Ca2+.
important Compare between ventricle cells and sinus node cells Ventricle cells Sinus node cells depolarization(phase 0)
Na+
Ca 2+
Phase 1
K+
No
Phase 2(plateau)
Ca 2+
No
Repolarization(phase 3)
K+
K+
Phase 4
Na+-K+pump
Ca 2+
Speed of depolarization
rapid
slow
overshot
+30 mV
0
Resting potential
-90 mV
No
K+
Repolarizaiton potential NO
- 60 mV
function
pacemaker
contraction
Overview of specific events in the ventricular action potential
Overview of specific events in the action potential of pacemaker cell
CHARACTERISTICS OF AP’S IN SKELETAL AND CARDIAC MUSCLE CELLS
Rhythmical excitation of the heart 1. Electrical activity of the heart 2. Electrophysiological properties 3. Electrocardiogram (ECG)
1.Electrical activity of the heart
1) Resting membrane potential 2) Action potential
Types of cardiac cell Working cells Atrial myocytes Ventricular myocetes Conducting cells SAN AVN His bundles Purkinje fibers
Recall: Outward current o positive ion efflux or negative ion influx o Bring membrane potential to hyperpolarized state
Inward current o Positive ion influx or negative ion efflux o Bring membrane potential to depolarization state
Ion Concentration Ion
Extracellular Intracellular
E
(mmol)
(mmol)
(mV)
K+
4
135
-94
Ca2+
2
0.0001
+132
Cl-
104
9
-65
Na+
145
10
+70
1)Resting membrane potential Equilibrium potential: At rest, the cardiac muscle membrane is highly permeable to K+ and almost impermeable to the others. The contractile cell’s resting potential is about – 90mV.
2)Action potential
a. Contractile cell
b. autorhythmic cell
a. Contractile cells: Phase 0
deploarization, upstroke From –90 mV to +30 mV Duration 1–2ms, APA ~120mV, Speed of depolarization 800-1000V/s
Phase 1 Early rapid repolarization MP from +30 mV to 0 mV Duration ~10ms Spike shape
Phase 2
Plateau, slow repolarization MP is ± 0mV Duration 100150ms Determine ADP
Phase 3
Terminal repolarization Late repolarization MP from 0 mV to –90 mV Duration 100-150ms
Phase 4
Resting state MP -90mV
Ionic Mechanisms Underlying the Action Potential
Phase 0 Voltage-gated sodium channel open
Phase 1 Phase 1 (fast repolarization phase 1) Sodium channel inactivated Transient outward current activated. Carried by potassium
Phase 2
Phase 2 (plateau phase) MP stayed at ± 0 mV resulting in a plateau Inward component: Ca2+ Outward component:
K+ efflux (Ik ） +
Ca2+ influx(ICa
， L
）
Phase 3 Phase 3 (Repolarization) Ca2+ channel closed K+ channels are activated Rapid K+ efflux resulting in repolarization bringing membrane potential to its resting
Phase 4
MP tends to a stable state Na+/K+ pump is activated Ca2+ pump is activated
summary
Depolarization is very rapid & is due to the inward diffusion of sodium (0). Repolarization begins with a slow outward diffusion of potassium, but that is largely offset by the slow inward diffusion of calcium (1 & 2). So, repolarization begins with a plateau phase. Then, potassium diffuses out much more rapidly as the calcium channels close (3), and the membrane potential quickly reaches the 'resting' potential (4), which is due to the Na+K+- pump.
b. Autorhythmic cells(sinus node) Autorhythmic cells exhibit PACEMAKER potentials.
The key to the rhythmical firing of pacemaker cells is that, these cells will slowly depolarize by themselves.
Phase 4
There are several kind of currents that contribute to spontaneously depolarization at phase 4 in pace-maker cells of SAN. An outward flow or "leak" of K+ ions, declining with the time goes on. An inward flow of Ca2+ . This relatively slow depolarization continues until the threshold potential is reached ( -40 mV ~ -50mV.
Phase 0 The SA node do not have fast sodium channels. The depolarisation in phase 0 is mainly caused by a slow influx of Ca2+ ions via voltage-gated Ca2+ channels, that opened when the threshold was reached.
Phase 3 The Ca2+ channels are inactivated, soon after they opened. Repolarization starts when the K+ channels open, allowing efflux of K+ that renders the interior of the cell negative.
summary Depolarization is due to the slow calcium channels open (0). Repolarization
is due to the outward diffusion
of potassium (3). During
phase 4 there is a progressive reduction
in outward current of K+ and a steady inward current of Ca2+.
important Compare between ventricle cells and sinus node cells Ventricle cells Sinus node cells depolarization(phase 0)
Na+
Ca 2+
Phase 1
K+
No
Phase 2(plateau)
Ca 2+
No
Repolarization(phase 3)
K+
K+
Phase 4
Na+-K+pump
Ca 2+
Speed of depolarization
rapid
slow
overshot
+30 mV
0
Resting potential
-90 mV
No
K+
Repolarizaiton potential NO
- 60 mV
function
pacemaker
contraction
Overview of specific events in the ventricular action potential
Overview of specific events in the action potential of pacemaker cell
CHARACTERISTICS OF AP’S IN SKELETAL AND CARDIAC MUSCLE CELLS
Related Documents
Electrical Activity Of The Heart
July 2020 2
Electrical Axis Of Heart
May 2020 2
Electrical Sequence Of The Heart Ekg
November 2019 12
1. Electric Activity Of The Heart Handout
May 2020 4
Circumcision Of The Heart
April 2020 34