Sino-atrial node - SA node
Pacemaker of normal heart. Produces impulses 60-100/min.
Travels along internodal pathways and cause contractions of walls of the
atrium.
Atrial Ventricle node - In center of heart - AV node or AV junction
Delays 1/10 of a second getting thru the AV node to allow atrium to finish contraction
Bundle of HIS - right under AV node, in both R & L vents
Impulse divides and travels down both sides of septum - called Right & Left bundle branches
Purkinje fibers line sides of ventricles and cause vent. contractions.
If SA node fails, normally AV node will take over - but slower, 40-60/min.
If AV node is wiped out - BUNDLE OF HIS can take over but it's even slower.
Both bundle branches can produce electrical impulses, as could Purkinje fibers. But at PURKINJE its beating around 15/min.
Other places thru out heart along wall can produce impulses. These often produce extra beats.
V FIB - such chaotic firing, its bouncing off of everywhere and the only contractions it causes are very small quivers
Electric shock doesn't jump start the heart, but clears out all this random firing, so the heart can start again in an organized way.
