origin and conduction of cardiac impulse Flashcards
where does excitation of the heart originate?
pacemaker cells of the Sino atrial node
where is the SA node located?
the upper right atrium
what is the name for the rhythm a heart that is controlled by the SA node?
sinus rhythm
What ion is responsible for the pacemaker potential?
due to slow sodium influx through HCN channels
once the threshold is reached, which ion is responsible for the action potential produced?
calcium influx through voltage gated calcium channels
what ion is responsible for depolarisation in SA nodal cell
potassium efflux
where is the AV node located?
the base of the right atrium just above the junction between the ventricles and atria
explain the path of action potentials through the heart?
Electrical activity begins at the SA node and travels to the AV node.
There is then a delay to allow for atrial contraction before travelling to the bundle of his, down the left and right bundle branches to the purkinje fibres and eventually reaching the ventricular myocytes
what is the fastest point of cardiac conduction?
the purkinje fibers
what is the resting membrane potential in contractile myocytes?
-90mV
what is the rising phase of the action potential in contractile myocytes caused by?
- sodium influx
- phase 0
what is phase 1 of contractile myocyte action potential?
- transient potassium efflux and sodium channel closure
what is phase 2 of the contractile myocyte action potential
calcium influx
what is phase 3 of the cardiac myocyte action potential?
- closure of calcium channels
- potassium efflux
what is phase 4 of the contractile myocyte action potential?
resting membrane potential
what is phase 2 of the contractile myocyte action potential also called?
plateau phase
what does the p wave represent?
- atrial depolarisation
what does the QRS complex represent?
ventricular depolarisation
why is atrial repolarisation not seen on an ECG?
it is masked by the QRS complex
what does the T wave represent?
ventricular repolarisation
what does the PR segment represent?
AV nodal delay
what does the ST segment represent?
ventricular systole
what does the TP interval represent?
diastole
how does the sympathetic nervous system affect the heart?
increases heart rate and force of contraction
