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صفحه 2:
PHYSIOLOGY OF CARDIAC
MUSCLE
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d- trial wuscle
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صفحه 3:
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Vke spevidized excittiory ond coorductive Pibers
Pibris
Cxhibit cutowetio مار( elevidodl discharge fo thePore pF uvtiod
potectiaks
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صفحه 4:
CARDIAC MUSCLE AS SYNCYTIUM
INTERCALATED
DISC
Ht Fok of Nic Poy. 120 fbn
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مسسس .00 iM 2011 by Smnsers on erp
Figure 9-2 °Sy Poe interconnecting nature of cardiac muscle bers.
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صفحه 5:
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وه مت اه توح موی لته 297
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thot unica potectas travel eusily Proow vor
pordac wuscle cell to the cext
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۱
ACTION POTENTIAL IN CARDIAC MUSCLE
+25
Transmembrane polenta,
1
0
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0
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a + + م مج م +ع tte که
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Phases of cellular action potentials and major associ 0 یی
ated currents In ventricular myocytes. The initial phase (0) spike and
overshoot (1) are caused by a rapid inward sodium (Na+) current, the
Plateau phase C2) by a slow calcium (cas) current through b-typ=
Ca channels. and repolarization (phase 3) by outward potassium: GS")
currents. Phase 4, the resting potential (Na* efflux, K> Intux), is main—
tained by Na*-K‘-adenosine triphosphatase (ATPase). The Na+-Ca?~
exchanger is mainiy responsible for extrusion of Cal. In specialized
conduction system tissue. spontaneous depolarization takes place dur
ing phase 4 until the voltage resuluing im opening of the Mia channel! is
reached. (From LeWinter MIM, Osol G: Normal physiology of the cardio
vascular system. In Fuster V, Alexander RW, O'Rourke RA, editors: Hurst's
the heart. ed 10. New York, 2001. McGraw-Hill, pp 63-942
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Phase 0 (rapid depolarization)
External stimulus to excitable tissue
opens the voltage gated sodium ion channels
sodium ions enter the cells down their
electrochemical gradient
intracellular movement of sodium ion
depolarizes the membrane
increases the membrane conductance to sodium ion
displaces the membrane potential to +30mV
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Phase 1 (early repolarization)
Following phase 0, the membrane repolarizes
rapidly and transiently to almost 0 mV because of
the inactivation of sodium ion channel and
simultaneous transient increases in outward
potassium currents
Phase 2 (plateau)
Membrane potential remains approximately 0 mV
for a relatively prolonged duration
A balance between slow inward Ca2+ and outward
K+ currents mediates the plateau phase of the..
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Phase 3 (repolarization)
Inactivation of Ca2+ channels and a simultaneous
increase in outward K+ current through K+
channels produces a net outward movement of
positive charge and repolarization of the membrane
Phase 4 (resting membrane potential)
The membrane potential of ventricular myocytes
remains at the resting membrane potential until the
cell is stimulated again
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The types of action potential in the heart can be
separated
into two categories:
(1) fast-response action potentials, which are
found in
the His-Purkinje system and atrial or ventricular
cardiomyocytes
(2) slow- response action potentials, which are
found in
the pacemaker cells in the SA and AV nodes
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SINOATRIAL NODE FIBER VENTRICULAR MUSCLE FIBER
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Specialized Excitatory and Conductive System
of
tha ern
>
A-V node
A-V bundle
۱ Left
Internodal 5 ِ “ bundle
pathways. / / branch
Right
bundle
fppticom
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A. SA NODE
The sinus node/ sinoatrial node is located in the
superior posterolateral wall of the right atrium
immediately below and lateral to the opening of the
superior vena cava
The sinus nodal fibers connect directly with the
atrial
muscle fibers so that any action potential that
begins
in the sinus node spreads immediately into the
atrial
mieccle wall
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B. INTERNODAL PATHWAYS و
Anterior (Bachmann)
Middle(Wenckebach) سس
Posterior(Thorel) internodal pathways
C. AV NODE
The A-V node is located in the
posterior wall of the right atrium
immediately behind the tricuspid
valve
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D.PURKINJE FIBERS
Velocity of conduction is 1 to 4m/sec
The ends of the Purkinje fibers penetrate about one
third of
the way into the muscle mass and finally become
continuous
with the cardiac muscle fibers
Once the impulse reaches the ends of the Purkinje
fibers, it is
transmitted through the ventricular muscle mass by
۶ ee,
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fppticom
TRANSMISSION OF CARDIAC IMPULSE
THROUGH THE
HEART
-
- 5
” كت
.
۰
=)
- J
> 5
۶ ]
=)
=
=)
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CONDUCTION SPEEDS IN CARDIAC TISSUES
0.05m/sec
1m/sec
0.05m/sec
Im/sec
4m/sec
1m/sec
SA Node
Atrial pathways
AV Node
Bundle of his
Purkinje fibers
Ventricular muscle
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BSE SER SR OR RRO
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The END
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