stands for Electrocardiogram, and records heart’s electrical activity.
When resting cardiac cells are electrically polarized, maintained by membrane pumps.
Cardiac cells loose negativity thru
fundamental electrical event of the heart, flow
of electricity across heart, detected by electrodes
is restoring polarity
- electrical power house of cell, 5-10µm, no true resting potential, dominant
ones in right atrium. Called
Sinoatrial (SA) node
and fire 60-100 times a minute, vagal will slow
it down and sympathetic speeds it up. Not seen on EKG
Electrical conducting cells
- hard wiring of heart, long and thin, carry current fast and efficiently
to distant regions of heart. Bachmans bundle rapid activation of left atrium from right
- contractile machinery of heart, contract and relax which delivery blood to the
body. 50-90µm, contain actin and myosin Excitatory Contraction Coupling- when myocardial cell
gets Ca2+ it contracts, less efficient at transmitting electric signals. Seen on EKG
– one cycle of depolarization and repolarization
Duration in fraction of second, Amplitude in milivolts, Configuration refers to shape.
– 0.04 seconds, .1mV on vertical axis
- 0.2 seconds,.5mV on vertical axis
Sinus Node fires spontaneously, not visible on EKG, wave of
depolarization spreads out, and when myocardial cells depolarize there’s an atrial contractions,
electrode placed on body can records burst of electrical activity (p-wave) .
SA node in right
right atrium depolarizes before left atrium. First half of p wave is right atrial
depolarization and second half is left atrial depolarization.
Electrical Gate at junction between atria and ventricles, current must be funneled thru
interventricular septum, which separates right and left ventricles,
Atrioventricular node (AV)
slows conduction, (slowed by vagal and sped up by sympathetic) pause lasts fraction of a
second so atria finish contracting before ventricles being contracting.