Electrophysiology Flashcards
what is the resting membrane potential for the ventricular action potential
-90mV
what creates a plateau on the ventricular conduction system
sustained period of depolarisation when there are equal influx and efflux of postivie and negative ions
what are the L type calcium channels
those that are slow to open and slow to close
when does potassium leave the cell
during action potential
describe depolarisation of ventricles
sodium enters the cell to give 20mV potential
calcium channels contribute toward the end of the upstroke
sodium channels are inactivated quickly
describe phase one of the ventricular action potential
small repolarisation because the sodium channels are inactivated but there are potassium ions leaving the cell
describe phase two of ventricular action potential
the plateau - calcium ions are continuing to enter the cell at the same time as the potassium ions leaving which balances out the current to allow for sustained depolarisation
describe phase three of ventricular action potential
calcium ions closed at the end phase two, but potassium ions are continuing to leave the cell, and there is repolarisation
describe phase four of ventricular action potential
resting membrane potential
what is the relative refractory period
the period near the end of action potential whereby if there is a strong stimulus it would be possible for there to be another action potential generated
do the nodal cells of the heart need nerves to generate their action potential
no, they can spontaneously depolarise and generate action potentials without the help of the nervous system
why can cardiac conduction cells generate their own action potentials
their resting potentials naturally drift toward the threshold to fire action potentials because their membrane is leaky
describe upstroke in conducting cells
calcium ions enter the cell slowly, making upstroke slower and less steep than in the contractile cells
describe phase 0 of the sino atrial node conduction
calcium ions enter the cell
describe phase 3 of the sino atrial node conduction
calcium channels have closed, but potassium ions continue to leave the cell
describe the funny current
the sino atrial node membrane is leaky and allows sodium to leak into the cell, which causes slow upstrake during phase four to allow for spontaneous depolarisation
what causes spontaneous depolarisation in the sino atrial node
the funny current
why does the sino atrial node set the rhthym rather than the other nodal cells
it has the fastest discharge rate of action potential so it sends the action potentials to the others before they have time to generate their own
describe the effect of the nervous system on the cardiac conduction system
it does not initiate the conduction, but it can change the rate of it
what are the five waves on an ECG
P
Q
R
S
T
how can the waves above the baseline be described as
positive deflections
what is the baseline of the ECG
isoelectric
which waves are positive deflections
P R and T
which waves are negative deflections
Q and S
what is the P wave
atrial depolarisation, just before the contraction of the atria
what is the QRS complex
ventricular depolarisation
where can atrial repolarisation be found on the ECG
buried in the QRS complex
what is the T wave
ventricular repolarisation
what are the two segments found on an ECG
PQ and ST
describe the PQ segment
end of atrial depolarisation to the start of ventricular depolarisation
describe the ST segment
plateau of the ventricular action potential
what is the J point
the junction between the end of the S wave and the beginning of the ST segment
what is the PQ interval
the interval from the start of the P to the beginning of the Q wave. the start of atrial depolarisation to the onset of the ventricular depolarisation
what is the QT interval
the onset of the Q wave to the end of the T wave
what is the RR interval
one cycle to the next, and it used to calculate heart rate
what is represented by the end of the T wave
the end of ventricular repolarisation
how long is each small square on ECG paper
0.04 seconds
how long is represented by larger boxes
0.2 seconds
how many mV in every ten small boxes
1 mV
what is the rate of the ECG paper
25mm recorded a second
