1. Overview of the Heart
The Cardiac Cycle and Electricity

2. Anatomy of the Heart
The heart is made primarily of 4 chambers:
Right Atrium
--Fills the Right Ventricle with
deoxygenated blood via the Tricuspid
Valve
Right Ventricle
--Pumps blood to lungs for Oxygen
via the Pulmonary Artery
Left Atrium
--Receives Oxygen-rich blood from
lungs via the Pulmonary Veins, and fills
the Left Ventricle with blood via Mitral
Valve
Left Ventricle
--Pumps the blood through the
Aorta and to the rest of the body

3. Blood Flow in the Heart

4. Electrical System of the Heart
The electrical system of the heart begins
in the Sinoatrial Node (SA node), which lies
in the top right corner of the right atrium.
(Top left of the illustration) The SA node is
also known as the pacemaker of the heart.
An electrical impulse is fired from the SA
node, and carried down special electrical cells
which form Purkinje fibers. (The Purkinje
fibers act as wires or cables, carrying the
electricity throughout the heart in specific
patterns.) This causes the Left and Right
Atria to contract, topping off the Ventricles
with blood.
The current flows from the SA node, to
the Atrioventricular Node (AV node) at the
bottom left corner of the Right Atrium. The
AV node then generates another impulse,
which is carried through the bottom portion
of the heart, causing the left and right
ventricles to contract.

5. Electricity in Cardiac Myocytes
The cells of the heart (cardiac myocytes) all conduct electricity. This is how the
electrical signals which travel through the Purkinje fibers can cause entire
chambers to contract.
In and around heart cells are many
ions of different elements. The flow of
these ions in and out of the cell are
what create an electrical charge. The
ions travel through the cell membrane
using special proteins which act as
channels.
When specific ion channels are activated, ions of higher
concentration outside the cell flow in rapidly, and ions of
higher concentration within the cell flow out rapidly
creating a spike in electrical energy. This process is
known as “depolarizing” because the ion concentrations
inside and outside of the cell create positive and negative
poles. When the ion channels are opened, the ions flow
freely balancing out the charge.

6. EKG Rhythms
The electrical activity in the heart can be studied using an
electrocardiogram (EKG). An EKG measures the electrical impulses sent
through the different areas of the heart using electrodes taped to the patient’s
chest, and displays them with a line graph. The y-axis (vertical) of the graph is a
representation of measured electricity in millivolts (mV). The x-axis
(horizontal) of the graph represents time in seconds.
Each wave in a heartbeat is represented with a letter. The first small wave,
for instance, is labeled as the P-wave, and shows the depolarization of the right
atrium. The more extreme, pointed wave is known as the QRS-complex, and
shows the depolarization of the ventricles. The smallest wave at the end of a
complete heartbeat shows the repolarization of the atria. (Repolarization of the
heart cells occurs when specific ion channels open and close to make the inside
of the cell negative and the outside positive.)

7. Sources
Biology: God’s Living Creation, Keith Graham and Gregory Parker
Principles of Anatomy and Physiology, Tatora Grabowski
https://www.youtube.com/watch?v=mcU-zUsSGH0
https://www.youtube.com/watch?v=fZT9vlbL2uA
https://www.youtube.com/watch?v=sPT7xB-3-z0
http://www.youtube.com/watch?v=vPvN7SmLrjs
http://www.youtube.com/watch?v=GjkrNQJGqvs
http://www.youtube.com/watch?v=84PrHxJri9Q