section 3, chapter 15
DESCRIPTION
cardiovascular systemTRANSCRIPT
Electrocardiogram
An electrocardiogram, or ECG (or EKG) is a recording of the electrical changes in the myocardium during the cardiac cycle.
Section 3, Chapter 15
P Wave
• Represents atrial depolarization
• Leads to atrial contraction
• Conduction of electrical impulse
from right to left and downward
QRS Complex
• Represents depolarization of
ventricles
• Leads to ventricular contraction
• This massive wave hides the atria
repolarization
Electrocardiogram
from right to left and downwardrepolarization
T Wave
• Represents repolarization of
ventricles
Electrocardiogram
Figure 15.22d. An ECG pattern with the corresponding systole and diastole shown above.
ECG of a regular heart rhythm at 75 beats per minute
Heart Arrhythmias:
normal
ECG of a regular heart rhythm at 75 beats per minute
Atrial Flutter. Atria fire 250-350 times per minute. For every QRS
complex there may be 4 or more P waves.
Bradycardia – cardiac rhythm less than 60 beats per minute.
Examples of Heart Arrhythmias. Arrows indicate p Wave.
Bradycardia – cardiac rhythm less than 60 beats per minute.
Tachycardia– cardiac rhythm greater than 100 beats per minute.
Atrial fibrillation. Instead of contracting, the atria become quivering
chambers. The ventricles respond only to impulses that make it to the
AV node.
Examples of Heart Arrhythmias, fibrillation
Ventricular fibrillation = Life threatening arrhythmia. Ventricles quiver, and are
unable to pump blood properly. Requires immediate defibrillation.
The heart rate is controlled intrinsically by the SA
node, but sympathetic and parasympathetic fibers
alter the rate at which the pacemaker fires.
Regulation of cardiac cycle
Cardiac Control Center
• Within Medulla Oblongata
• Receives sensory impulses from throughout the cardiovascular system and relays motor impulses to heart in response.
• Cardioinhibitor & cardioaccelerator reflex centers
• Cardioinhibitor reflex center
– Parasympathetic fibers from vagus nerves innervate SA & AV nodes.
– Acetylcholine (ACh) released from fibers decreases the firing rates of SA
& AV nodes.
– Heart rate decreases
• Cardioaccelerator reflex center
– Sympathetic fibers from accelerator nerves innervate SA & AV nodes.
– Norepinephrine released from fibers increases the firing rates of SA & AV
nodes.
– Heart rate and force of contraction increases
Cardioinhibitor & cardioaccelerator reflex centers alter the heart
rate in response to sensory impulses from receptors
Baroreceptors – monitor blood pressure
• Within aortic arch and carotid sinuses
• Rising blood pressure stimulates cardioinhibitor center
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Figure 15.24b Illustration of the baroreflex arc
End of Section 3, Chapter 15