Electrical conductivity in heart :
SA node / pacemaker :-
• SA node present in right upper corner of right atria.
• It generates 0-100 impulse per minute but vagous nerve slows it to 70-75 per minute.
• Impulse spread from SA node to atrial valve and AV node.
AV node / Pacesetter :
• It present in left corner of right atria.
It maintain the speed of impulse passing to ventricle.
• AV bundle rises from AV node and cross AV septum.
• Then it divided into right and left branch along IV septum ( Intra Ventricular Septum ).
• They further divided to form Purkinje fibre in valve.
Bundle of his = AV bundle + right/left branch + Purkinje fibre
Note :-
• Human heart is myogenic and autorhythmic.
• Sympathetic nervous system increase heart rate.
• Para sympathetic nervous system decrease heart rate.
CARDIAC CYCLE
• It involves alternate contraction (called systole) and relaxation (called diastole) of heart at the rate of 70-72 imes per minute at rest.
• All the chambers do not beat simultaneously.
• Right and left auricles contract simultaneously while both ventricles also work simultaneously.
• The sequence of events that occur during one heart beat is called cardiac cycle.
Normal heart rate = 72 per minute
1 heart beat = one Cardiac cycle
One min.(60 second) =72 Cardiac cycle.
Therefore, 1 Cardiac cycle =60/72 =0.8 second.
Cardiac cycle is formed of 3 phases :
Arterial systole (0.1 second) :-
• SA node generate impulse which spread to artrial wall to intercalated disc and gap junction.
• Thus atria contract pushing blood into ventricles.
• AV valve are open and semilunar valve are close.
Ventricle Systole (0.35 second) :-
• Signal reaches to ventricle valve through Purkinje fibre.
• Ventricle contract and pressure increase in it compare to atria.
• Thus atrial valve close and produce first heart sound LUBB.
• Pressure goes on increasing and opens semilunar valve.
Joint Diastole (0.4 second) :-
• Both atria and ventricle are relaxing.
• At beginning of joint Diastole, semilunar valve close (second heart sound DUB).