The Heart’s Conduction

System

Structures

Nodes – tissue masses that generate a wave of electrical energy

Sinoatrial node (S/A node) – is found in the right atrium and initiates the heart beats and sets the rate of heart contractions. This is why is it often called the pace maker of the heart

Atrioventricular node (A/V node) – is found in the interatrial septum at the bottom of the right atrium. This node is stimulated by the electrical waves sent by the S/A node

Conduction Pathway

1. The S/A node generates an electrical impulse that begins the heart beat

2. The excitation wave travels throughout the muscle of each atrium, causing the atria to contract. At the same time, impulses travel directly to the A/V node by means of fibers in the wall of the atrium

3. The A/V node is stimulated. This is has a slower rate of conduction allowing the atria to contract and the ventricles to fill before the ventricles contract

Conduction Pathway Continued

4. The excitation wave travels rapidly through the bundle of His and throughout the ventricular walls by way of the purkinje fibers.

5. This causes the entire ventricular musculature to contract at the same time.

A normal heart rhythm

originating at the SA node is

termed sinus rhythm

Control of Heart Rate

Heart rate can be influenced by:

- nervous system

- hormones

- other internal factors

Heart Rate

Heart rate is one of the vital signs to determine someone’s health.

To determine someone’s heart rate we can take their pulse

Practice

Practice taking your own pulse using both locations

Practice taking the pulse of a partner using the location on the wrist

What is considered normal resting heart rate?

Autonomic Nervous System

The autonomic nervous system(ANS) plays a major role in modifying the heart rate according to need.

The sympathetic nervous system speeds up the heart rate in response to increased activity or during the fight-or-flight response.

This can increase cardiac output two to three times the resting value

ANS continued The parasympathetic nervous system decreases or

slows heart rate to normal levels

The parasympathetic nerve that supplies the heart is the vagus nerve. It slows the heart rate by acting on the SA and the AV node

Heart rate can also be affected by hormones, ions and drugs circulating in the blood

Exercise strengthens the heart and increase the amount of blood that can be pumped with each beat

Trained athletes usually have a lower resting heart rate

Variations in Heart Rates

Using your text book summarize the following variations in heart rate: (pg. 319)

1. Bradycardia –

2. Tachycardia-

3. Sinus arrhythmia –

4. Premature beat -