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=70QE1poMZ1E