2. Coronary Circulation and Electrical Activity of the Heart

coronary circulation

The heart is an organ so it needs a source of nutrients & oxygen and a way to get rid of wastes. This is called…

blood flow…

is NOT continuous

systole

When coronary vessels are compressed, the heart is in [term] (contracts), so the flow is diminished

diastole

Regular flow resumes when the heart is in [term] (relaxes)

coronary arteries

• delivers oxygenated blood to the heart wall during diastole

• the left and right ones are the first branches of the aorta

• have many anastomoses (connections between vessels)

major coronary veins

drains the deoxygenated blood from the heart wall during diastole

great cardiac vein

drains the left side of the heart

small cardiac vein

drains the right margin of the heart

coronary sinus

• all of the veins empty here

• empties blood into the right atrium

autorhythmic

the heart stimulates itself to contract at regular intervals

pacemaker cells

generate action potentials (APs) spontaneously

pacemaker potential

movement of K⁺, Na⁺, and Ca²⁺ causes spontaneous development of local potential

AP is generated

once the threshold is reached…

conducting cells

• specialized cells

• able to pass the AP through the heart

Sinoatrial node (SA node)

• Located in the right atrium just medial to the opening of the superior vena cava

• This is the pacemaker of the heart – origin of our heartbeat

• Generates AP that pass into the atrial muscle cells and then to the AV node

AV node

• in right atrium, near tricuspid valve;

• slowest conduction—delays signal so atria finish contracting

• APs are conducted here more slowly that anywhere else in the conducting system

• Gives the atria time to finish contracting before the signal is received by the ventricles

Atrioventricular bundle (AV bundle)

• Located in the superior part of the interventricular septum

• the only electrical connection between the atria and ventricles

right and left bundle branches

• Begin where the AV bundle splits into two branches

• Extend through the interventricular septum down to the apex

Purkinje fibers

• large myofibers of the Conducting Network

• located in the ventricle walls

• conduct the AP to the ventricular muscle cells

AP through the heart

what do these images show (study it)

Electrocardiogram (EKG)

• graphical record of the electrical events of the myocardium

• we can correlate the electrical events to the mechanical events

Important EKG events

P wave, QRS complex, and T wave

P wave

atrial depolarization

QRS complex

• ventricular depolarization

• At this time, the atria are undergoing repolarization, but it cannot be seen on an EKG because ventricular depolarization is a stronger electrical event

T wave

ventricular repolarization