How does the heart function?
Control of the heart
The heart muscle
• The heart is made of cardiac muscle
• It is involuntary and controlled by the
medulla oblongata
• The intercalated discs help cardiac cells
contract uniformly
Action Potentials
• Like other types of muscle, cardiac cells respond to
nerve impulses
• Changes in Na+, K+, and Ca+ (electrolytes) are
essential for the cardiac cells to respond to the nerve
signals
• Unlike skeletal muscle cells, which respond within 2ms,
cardiac cells take 200 to 500 ms to respond
Autorhythmicity
• The sinoatrial (SA)node stimulates the heart cells to
contract
• The SA node is made of specialized cardiac cells
• It is the “Pacemaker” of the heart because it generates
action potentials that cause the heart to beat
The Conducting System of the Heart
• 1. Action potentials start in the SA node
• 2. The impulse travels across the walls of the atrium to
the AV (Atrioventricular) node and the atria contract
• 3. The AV node passes the impulse to contract to the
ventricles
• 4. The ventricles contract after a delay of about .11
seconds
Why do you think
there is a delay
before the ventricles
contract?
So the atria can finish
passing the blood to the
ventricles
The AV Bundle
• The AV node forms the AV bundle, a collection of
modified cardiac fibers, that extend into the
interventricular septum and beyond
• The AV bundle leads to smaller Purkinje fibers which
extend throughout the apex and ventricular walls
The Purkinje Fibers are
specialized to spread the
contract impulse very rapidly
What is an EKG???
• EKG (ECG) stands for electrocardiogram
• EKG’s show the sum of all the heart’s action potentials
• EKG can show abnormal heart rates and rhythms,
blockages, and damage to parts of the heart, possibly
caused by “heart attacks.”
• It is easy to perform and painless for the patient
Systole and Diastole
•
•
•
•
•
Systole:
Occurs when the ventricles are actively contracting
The AV valves are closed
Semi-lunar valves are open
The atria are relaxed
Diastole:
•
•
•
•
Occurs when the atria are actively contracting
The AV valves are open
The semi-lunar valves are closed
The ventricles are relaxed
Disorders of the heart . . .
• When a coronary blood vessel becomes blocked, heart
tissue can die from lack of oxygen in minutes
• This region of dead tissue is called an infarct
• A “heart attack” is technically a myocardial infarction
• If recognized and treated early, the heart tissue may
suffer little or no permanent damage
http://www.youtube.com/watch?v
=n8P3n6GKBSY
Causes of Coronary Artery Disease
Treatments for Occlusions (Blockages):
• Angioplasty: a balloon is inserted into blocked arteries
and inflated, flattening the plaques
• Stent: a small coil device placed in a vessel after
angioplasty
• Coronary Bypass: healthy blood vessels taken from
other parts of the body “bypass” or go around the
obstruction.
Cardiac Arrhythmias (Abnormal Rhythms)
• Tachycardia: elevated heart rate, beats > 100/min
• Bradycardia: slow heart rate, beats <60/min
• Atrial Fibrillation: atria quiver or flutter instead of
making strong regular contractions
http://www.youtube.com/watch?v=
N1tcH_07GYk
http://www.youtube.com/watch?
v=w57gIV3ZLBE
http://www.youtube.com/watch?v=70QE1p
oMZ1E