Lec 19 Flashcards
Myocyte (99%) AP
-Resting potential-90 mv
-AP initiated when depolarization enter cell
-Ap divide in 5 phase (0-4)
-Long AP duration (200msec)
Systematic part of blood pump
Left Ventricle
Long AP duration in cardiac
-Prevent summation
-Ensure that heart contract/relaxed before it can contract again
Main channels in ventricular AP
Voltage gated Na channel
Voltage gated Ca channel
Slow/medium/fast voltage gated K channels
AP ion channels process
Phase 0:
- pacemaker cell trigger Na channel opening
- Na rushes in
Phase 1: (Notch)
- Na channels inactive
- little repolarization due to fast K channel opening
Phase 2: (plateau)
- high permeability to Ca (flow in)
-low permeability to K (flow out) -(medium K channel)
-2 current with opposite direction
Phase 3: (repolarization)
- slow K eventually open
-Ca channel inactive
Phase 4:
-k leak channels
-Na/K ATPase
Rest (necessary resting potential (-90mv) should be reach before triggering Na channels again
Absolute refractory period in cardiac
Na channels inactive
Second response not possible regardless of strength
Relative refractory period cardiac
K channels are bringing the resting voltage potential to normal value(-90mv)
- secondary response can elicit but at greater cost-need high strength
Why ventricular myocyte action potential is longer?
Prevent summation will ensure that heart act as pump
Cardiac vs skeletal in refraction period duration
Cardiac long refractory period, no summation
Skeletal very short refractory period, exhibit summation
Pacemaker (1%) AP
1- Na go in until reach threshold(-40mv)
2- depolarization: Ca ion in
3- Ca will inactivate (20mv)
4- K channels open (k out)
5-pacemaker potential in -60mv: I(f) current trough funny channels (HCN channels)
6- conduct both Na and K ions
7- Na has bigger flux to go in
8- Na in flux will reach threshold
Pacemaker potential is
Between APs
Pacemaker AP in SA node then
Autorhythmic cells spontaneously fire
And spread by intercalated disk with gap junction
Conducting system of the heart
1-SA node
2-Internodal Pathway —atria contract
3-Av Node
4-Av bundle(Bundle of His)
5-Bundle branches
6-Purkinje fibers
7- ventricular muscle cell
8-Ventricular contract from bottom to up
AV nodes
Pause button
Wait for atria to finish contract
Only pathway from atria to ventricle
Pacemakers in heart
Major: SA node
—Pace of heartbeat (70bpm)
Minor:
1- AV node
—can takeover but weaker (50bpm)
2- Purkinje
—can takeover but weakest (30bpm)
