The Conducting System and EKGDanny Golinskiy, Joel Levy, Emily Brames

The Conducting System Cardiac muscle contracts regardless of

neural input (autorythmicity) All cardiac contractions are

coordinated by the heart’s conducting system

The conducting system is a network of specialized cells that initiate and distribute electrical impulses in the heart

The network is comprised of two cells that do not contract: nodal and conducting cells

The Conducting System Nodal cells establish the rate

of cardiac contraction (located at the sinoatrial and atrioventricular nodes)

Conducting cells distribute the contractile stimulus to the general myocardium

Major cardiac sites for the conducting cells include the AV bundle, bundle branches, and Purkinje fibers

The Conducting System Nodal cells depolarize spontaneously and

generate action potentials at regular intervals

Nodal cells determine the heart rate by sweeping the cardiac tissue

The normal rate of contraction is established by pacemaker cells, which reach the action potential threshold first, and are located in the sinoatrial node, referred to as the cardiac pacemaker

The Conducting System Pacemaker cells generate 70-80

action potentials a minute through spontaneous and rapid depolarization

The cells of the SA node, which houses the pacemaker cells, are connected to the larger antrioventricular node (AV node)

AV nodal cells generate only 40-60 action potentials per minute and can become the primary pacemaker cells if they do not receive input from the SA node

The Conducting System From the AV node action potential travels

to the AV bundle, which divides into left and right bundle branches that radiate across the inner surfaces of the ventricles

It takes an action potential about 50 milliseconds to travel from the SA node to the AV node

The action potential travels through cell to cell contact

The Conducting System Bradycardia: the heart rate is slower

than normal (60bpm or less) Tachycardia: the heart rate is faster than

normal (100bpm or more) Ectopic pacemaker: the origin of

abnormal signals

Electrocardiogram (EKG or ECG) An EKG is a device that records the electrical

events of the heart. Each time the heart beats a wave of

depolarization passes through the heart muscle & this activity is recorded on the EKG.

Leads are placed on the chest & limbs to obtain an EKG.

Electrocardiogram (EKG or ECG) EKG is “read” by medical

personnel to monitor the electrical activity of a patient’s heart.

Each heart beat has the following major components:

→ P-Wave – represents the depolarization of the atria.

→ QRS Complex - results when the ventricles depolarize.

→ T-Wave – indicates repolarization of the ventricles , the ventricles are returning to a resting state.

Electrocardiogram (EKG or ECG)When analyzing an EKG, the

clinician measures voltage & size of the different components of the EKG.

Electrocardiograms are also used to diagnose cardiac arrhythmias. Arrhythmias are abnormal patterns of cardiac activity.

EKG and the Conducting System

The image created by the EKG depicts the electrical cycle of the heart. The electrical

signals are derived from a release of electrical potential from high to low across the heart.

EKG and the Conducting System

The 3 parts of the EKG: P-wave: electrical discharge

across the atriums QRS-complex: this relates to

the electrical discharge or depolarization of electrical potential across the ventricles.

T-wave: Repolarization of heart, or restoring of the electrical potential in the membrane tissues of the heart.

EKG and the Conducting System

In the atrium: During the electrical

discharge (depolarization), discharged from the SA node to the AV node and spreads from the right atrium to the left atrium.

EKG and the Conducting System

The Ventricles: QRS Complex: Electrical

discharge of potential (depolarization) of the right and left ventricles.

T-wave: Restores the electrical potential (repolarization) across the ventricles through the heart.

Work Cited Bartholomew, Edwin F., and Frederic

Martini. Essentials of Anatomy & Physiology. San Francisco, CA: Benjamin Cummings, 2007. Print.

McDowell, Julie. Encyclopedia of Human Body Systems. Santa Barbara: Greenwood, 2010. Print.

Whittemore, Susan, and Denton A. Cooley. The Circulatory System. Philadelphia [Pa.: Chelsea House, 2004. Print.

Work Cited (Images) http://en.wikipedia.org/wiki/File:Sinus

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