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
- 0.2 seconds
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 atrium
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.
has electrical conducting cells made of 3 parts
Bundle of His-
from AV node and splits into
right and left bundle branches
current to right side of interventricular septum, to apex of the right ventricle. The
left bundle branch
which depolarizes interventricular septum and the
along anterior surface of left ventricle and the
sweeps over posterior surface of left
ventricle. The right and left bundle branches turn into
Terminal Purkinje Fibers
which deliver electrical
current into ventricular myocardium