CH 18 - Heart: EKG Activity

What is the average number of electrical impulses created by the SA node?

60-100 electrical impulses per minute.

What is an electrocardiogram?

A measurement of the electrical activity and impulses created by the heart.

What is the function of the AV node?

A small bundle of cells that can receive the electrical impulse from the SA node and continue the electrical signal down into the ventricles.

What does the P wave represent?

Depolarization and contraction of the right and left atria.

What does the QRS complex represent?

Depolarization and contraction of the right and left ventricles.

Explain how depolarization and repolarization occur. How do these relate to muscle contraction and relaxation?

Depolarization is caused by a flood of ions (sodium and potassium) across the cell membrane and drives the cells, therefore cardiac muscle tissues, to contract. Once the impulse has passed, the cardiac cells must reset to be able to send another impulse.

What could cause the SA node to increase the number of electrical impulses?

Oxygen depletion.

What does the T wave represent?

Repolarization and relaxation of the ventricles.

What are the three crucial parts of the cardiac conduction system?

The SA and AV nodes, and the His-Purkinje System.

Explain how an electrical impulse created in the SA node eventually leads to the contraction of the ventricles.

The SA node sends an impulse through both atria, causing them to contract and reach the AV node. The AV node continues to impulse, sending it down the Bundle of His, right and left bundle branches, and into Purkinje fibers within the ventricles causing both ventricles to contract.

What is the cardiac conduction system?

The electrical system in the heart that creates it's own nerve impulses without the brain.

What is the function of the SA node?

The pacemaker - small bundle of cells capable of starting the electrical impulse that will cause the heart to beat.

What is the sinus rhythm?

The rate at which your heart depolarizes and repolarizes.

What is the function of the His-Purkinje System?

These fibers actually carry the electrical impulse to the ventricles, causing a contraction. The impulse starts at the His bundle fibers, and continue the electrical signal down into the ventricles.

Explain how the up and down motion of the lines on an ECG grid represent the electrical activity of the heart.

They represent the repolarization and depolarization.