Download Heartbeat

It Keeps On Beating
Cardiac Cycle
• One complete sequence
of pumping and filling
• Contraction phase is
called systole
• Relaxation phase is
called diastole
• Average adult at rest
completes 75 cardiac
cycles per minute or 0.8
seconds per cycle
What Makes the Heart Beat?
•
Caused by electrical
impulses:
1. SA Node (sinoatrial node)
1. Pacemaker
2. Sets timing and rhythm of
heart beat
3. Sends electrical impulse
similar to nerve impulse
4. Triggers cells of both atria to
contract in unison
5. Impulse travels thorough
cardiac cells to AV node
(atrioventricular node)
What Makes the Heart Beat?
2. AV Node (atrioventricular
node)
1. Located in wall between right
atrium and right ventricle
2. Delays spreading the
electrical impulses for 0.1
seconds to ensure the atria
are completely empty
3. Sends impulses to
specialized muscle fibers and
Purkinje fibers, which
conduct signal to apex of
heart and induce ventricular
contraction