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.
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
Top Related