2. Impulse-Conducting System
• Contraction of cardiac muscle cells to eject blood is triggered by action
potentials sweeping across the muscle cell membranes
• Heart contracts or beats rhythmically as a result of action potentials
generates by itself, called autorhythmicity, or automaticity.
• There are 2 specialized types of cardiac muscle cells:
– Contractile cells: 99% cardiac muscle cells for mechanical
pumping, do not initiate action potentials
– Autorhytmic cells: do not contract but specialized for
initiating and conductiong the action potentials responsible
for contraction
pacemaker
3. Impulse-Conducting System
• Consist of specialized cells initiate heart-beat and
electrical contractions
– SA node (rate 70 – 80)
– AV Node (rate 40 – 60)
– Right and Left bundle branch (rate 20 – 40)
– Purkinje fibers
pacemaker
20-40 kali
kalo sa node bermasalah akan diambil alih av node (bisa tapi jadi inefisien) -> SSS (six sinus syndrome) -> heart rate turun -
cardiac output ngga cukup - pusing (mau pingsan)
SA node di atrium kanan di epikardial
WPW syndrome -> aksesori pathway
5. • Rhythmic contraction of the heart relies on electrical impulses along
conduction pathway
– Marker of electrical stimulation action potential
• 3 types of cardiac cells capable of electrical excitation:
– Pacemaker cells (SA node, AV node)
– Specialized rapidly conducting tissues (e.g. purkinje fibers)
– Ventricular and atrial muscle cells
• Sarcolema each of these cardiac cells is a phospholipid bilayer that is
impermeable ion serve as ion channels, passive cotransporters, and
active transporters.
– Maintain ionic concentration gradients and charge differentials between
inside and outside cardiac cells
Impulse-Conducting System
RBBB, LBBB -> QRS wavenya lebar karena
ngga lewat jalur khusus, cuma dari otot ke
otot
6. • Movement of specific ions across cell
membrane serve as basis of the action
potential
• Passive ion movement depends on:
–Energetic favorability
–Permeability of the membrane for ion
ION MOVEMENT AND CHANNELS
ion dalam otot jantung bekerja keluar masuk otot berdasar permeabilitas / voltage
7. ION MOVEMENT AND CHANNELS
• Energetics
– Direction of passive ion
flux driven by
concentration gradient
and transmembrane
potential (voltage)
8. ION MOVEMENT AND CHANNELS
• Permeability
– Cell membrane at its resting potential is not permeable to
sodium
– Membrane permeability is dependent on the opening of
specific ion channels (e.g. Na+, K+, Ca++)
– Voltage across the membrane determines what fraction of
channels is open
– Gating of channels is voltage sensitive
– Membrane voltages changes during depolarization and
repolarization of the cell, specific channels open and close
membran ada kanal ion khusus
10. ION MOVEMENT AND
CHANNELS
• Permeability
– At a voltage of -90 mV (ventricular muscle cell resting
voltage) channels are predominantly closed, Na+ ions cannot
pass through
– Rapid depolarization renders membrane potential less
negative and Na+ ions permeate through the open channels
– Activated channels remain open for only brief time, then
spontaneously close to inactive state
– Inactivated state persists until the membrane voltage
repolarized nearly back to its original resting level
11. RESTING POTENTIAL
• In nonpacemaker cardiac cells at rest, electrical
charge differential between inside and outside
cell corresponds to the resting potential
• Magnitude of resting potential depends on:
– Concentration gradients ions between inside and
outside the cell
– Relative permeabilities of ion channels that are open
at rest
12. RESTING POTENTIAL
• K+ concentration much greater inside cardiac cells
compared with outside
• Protein pump (Na+K+-ATPase) extrudes 3 Na+ ions out
of the cell exchange for the inward of 2 K+ ions
– Maintain intracellular Na+ at low levels and intracellular K+
at high levels
• K+ channels open in resting state when other ionic
channels are closed
– K+ flow outward direction down its concentration gradient
14. ACTION POTENTIAL
• Permeability cell
membrane to specific
ions changes because of
voltage-gating
characteristics of the ion
channels
• Each type of channels
has a characteristic
pattern of activation and
inactivation determines
progression of electrical
signal
15. ACTION POTENTIAL
• Cardiac muscle cell
– Resting potential remains stable, at
approximately -90 mV (resting state before
depolarization phase 4)
– Phase 0
• Na+ channels open, and rapidly enter the cell
• Transmembrane potential progressively less
negative
– Phase 1
• Brief current of repolarization during phase 1
returns membrane potential to approximately 0
mV
• Outward flow of K+ through a type of transiently
activated K+ channel
baru bisa bergerak kalo disenggol sama sel sebelahnya
diluar otot jantung lebih banyak natrium kalsium yang di dalem kalium
begitu pacemaker terdepolarisasi akan menghantarkan ke sel sekelilingnya -> mulai jadi positif sampe titik tertentu ->
pertama terbuka kanal natrium -> natrium masuk -> dalam otot jantung positif sampe ke atas -> kanal tertutup kalium
bekerja -> kalium keluar -> mulai turun
dalam keadaan resting stabil -90 mv
16. ACTION POTENTIAL
• Cardiac muscle cell
– Phase 2
• Long “plateau” phase mediated by the balance of
outward K+ currents, in competition with an inward
Ca++ current through specific L-type calcium channels.
• L-type calcium channels begin open during phase 0,
when membrane voltages reaches approximately -40
mV
• The near equalty current Ca+ inward and K+ outward
resulted membrane voltage does not changes
• As the Ca++ channels gradually inactivate and efflux of
K+ exceed influx of Ca+ then phase 3 begins
kanal dua"nya terbuka -> kalium keluar kanal kalsium terbuka (fase plateau)
17. ACTION POTENTIAL
• Cardiac muscle cell
–Phase 3
•Repolarization returns the
transmembrane voltage back to resting
potential approximately -90 mv.
•Phase 3 completes action potential
cycle, return to phase 4 preparing the
cell for next stimulus for depolarization
kalsium tertutup tersisa kanal kalium
18. ACTION POTENTIAL
• Pacemaker cells
–SA node and AV node
–Self-initiated depolarization in a
rhythmic fashion automaticity
–Cells undergo spontaneous
depolarization during phase 4, when
threshold voltage is reached, action
potential upstroke is triggered
-60
perlahan dalam keadaan resting potensial aksi -60. ada
sel natriu kalium masuk yang menyebabkan dalam sel
semakin positif. dalam sel pacemaker ada voltage gated.
begitu mencapai -40, kanal kalsium terbuka. terus banjir k-
kalsium masuk ke dalam sel jadi positif. kanal kalium
kebuka keluar kalium jadi negatif lagi pelan".
ada nak atpase, natrium kalsium cotransporter ->
menyeimbangkan
19. ACTION POTENTIAL
• Pacemaker cells
–Maximum negative voltage is
approximately -60 mV, persistently
negative membrane voltage causes
fast sodium channels remain
inactivated
–Phase 4 has an upward slope,
representing spontaneous gradual
depolarization known as pacemaker
current predominantly by Na+ ions.
20. ACTION POTENTIAL
• Pacemaker cells
– Phase 0 upstroke less rapid and reaches
lower amplitude than cardiac muscle
cell. Resulted from fast sodium
channels being inactivated and the
upstroke action potential relying on
Ca++ influx through relatively slow
calcium channels
– Repolarization occurs similar to
ventricular muscle cells, relies on
inactivation of calcium channels and
increased activation of potassium
channels with enhance K+ efflux
21. REFRACTORY PERIODS
• Cardiac potential longer in duration,
supporting prolonged Ca++ entry and
muscle contraction during systole.
• Results in prolonged period of
channel inactivation during muscle is
refractory to restimulation
• This long period allows ventricles
have sufficient time to relax and
refill before next contraction
absolute RP -> walaupun dirangsang dengan voltage
berapapun tidak akan terdepolarisasi
relatif RP -> di fase 3 terutama -> sudah mulai istirahat ->
kalo dirangsang lagi dengan kekuatan lebih tinggi bisa
terdepolarisasi lagi
kanal natrium semua kebuka
22. REFRACTORY PERIODS
• As phase 3 action potential progresses, increasing number
of Na+ channels recover from inactivated to resting states,
then open in response to the next depolarization
• Absolute refractory period refers to period cell completely
unexcitable
• Effective refractory period includes absolute refractory
period include a short interval of phase 3, which
stimulation only produces a localized action potential
• Relative refractory period is the interval during stimulation
triggers an action potential is conducted, but the rise of
action potential is lower because some Na+ channels are
inactivated and some delayed rectifier K+ channels remain
activated, thus inward currect is reduced
• Short “supranormal” period is a less-than-normal stimulus
can trigger an action potential
23. IMPULSE CONDUCTION
• During depolarization, electrical impulse
spreads rapidly along each cardiac cell,
connected through low-resistance gap
junctions
• Speed of tissue depolarization and
conduction velocity depend on inward
current (largely sodium channels)
• Tissues with high concentration of Na+
channels (e.g Purkinje fibers) have a
large and fast inward current support
rapid conduction
av node pelan biar darah atrium sempet masuk ventrikel sebelum
listrik lanjut his purkinje sebelum ventrikel berkontraksi
atrium fibrilation -> kalo heart rate atrium sangat tinggi (200-300),
nggabisa masuk ke ventrikel karena ada perlambatan di av node
jadi heart rate ngga terlalu tinggi
24. REFERENCES
• Human Physiology: From Cells to Systems, Ninth
Edition. Lauralee Sherwood
• Pathophysiology o heart disease (Lilly);
Pathophysiology o heart disease : a collaborative
project o medical students and aculty / editor,
Leonard S.Lilly. — Sixth edition.
