Cardiovascular Cycle & EKG
The heart can be considered a 4-chamber double-pump system
Unlike other muscular contractions in the body, the cardiac cycle does not require a nerve stimulation to make the heart muscle contract.
This means that the heart makes itself contract and this is called a myogenic contraction.
Your heart's electrical system should maintain:
- A steady heart rate of 60 to 100 beats per minute (bpm) at rest.
- The heart's electrical system also increases this rate to meet your body's needs during exercise and lowers during sleep.
- An orderly contraction of your atria and ventricles (this is called a sinus rhythm).
Heart Beat
The heart generates its own electrical signal (also called an electrical impulse)
The heartbeat happens as follows: Start #1
#2 The Sinoatrial node (SA node) (called the pacemaker of the heart) sends out an electrical impulse through the walls of the atria (left and right sides) to a second group of specialist cells.
The electrical signal spreads across the right atrium and the left atrium (the top two chambers of the heart), causing both atria to contract, and to push their load of blood into the right and left ventricles (the bottom two chambers of the heart)
The impulse takes approximately 50 ms (milliseconds) to travel between this node and the AV node.
The total time elapsed from the initiation of the impulse in the SA node until depolarization of the ventricles is approximately 225 ms.
#3 The Atrioventricular node (AV node) (called the gatekeeper) holds the impulse for a very short time and sends an impulse onward.
#4 Atrioventricular bundle (also known as The Bundle of His) divides into right and left pathways.
#5 These pathways are called Bundle Branches (right & left) descend and reach the apex of the heart where they connect with the Purkinje Fibres causing the depolarization of the ventricles and they contract.
This cycle of an electrical signal followed by a contraction is one heartbeat.
The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract.
PARTS OF THE HEART PRACTICE WORKSHEET
The electrical impulse of the heart can be recorded by placing electrodes on the chest. This is called an electrocardiogram (ECG, or EKG).
HEART SOUNDS
HEART VALVES are tissue-paper thin membranes attached to the heart wall.
They constantly open and close to regulate blood flow.
The
opening and closing cause the sound of a heartbeat- LUB-DUB
HEART BEATS
CARDIAC CYCLE PRACTICE WORKSHEET