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42 terms

Anatomy and Physiology Lab Ex 31 Conducting System of the Heart and ECG

STUDY
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True or False. Cardiac muscle cells are electrically connected by gap junctions and behave as a single unit.
True
Because it sets the rate of depolarization for the normal heart, the _________ node is known as the pacemaker of the heart.
sinoatrial (SA)
True or False. Activity of the nerves of the autonomic nervous system is essential for cardiac muscle to contract.
True
The typical ECG has normally how many recognizable deflection waves?
3
In a typical ECG, the __________ wave signals the depolarization of the atria immediately before they contract
P wave
True or False. Repolarization of the atria is usually masked by the large QRS complex.
True
A heart rate over 100 beats per minute is known as
tachycardia
How many electrodes or leads will you place on your subject for today's activity if using a standard ECG apparatus?
12
True or False. Electrical activity recorded by any lead depends on the location and orientation of the recording electrodes.
True
intrinsic conduction system
AKA nodal system of the heart, consisting of specialized noncontractile myocardial tissue. Components are the sinoatrial (SA) node, atrioventricular (AV) node, AV bundle (bundle of His), and bundle branches, and Purkinje fibers.
sinoatrial node (SA node)
has highest rate of discharge and provides stimulus for contraction. From SA node, the impulse spreads throughout the atria and to the AV node, which is immediately followed by atrial contraction.
atrioventricular node (AV node)
the impulse is momentarily delayed, allowing the atria to complete their contraction. Then passes through AV bundle
Electrocardiogram, ECG
the graphic recording of the electrical changes in heart activity, depolarization followed by repolarization, occuring during the cardiac cycle. Divided into segments and intervals. It is a record of voltage and time.
P-R interval
-time between the beginning of atrial depolarization and ventricular depolarization.
-Transmission of the impulse to contract from the SA node to the AV node and through the ventricles
-Longer interval suggests a part AV heart blocked caused by damage to AV node.
QRS complex
when prolonged may indicate a right or left bundle branch block when one ventricle is contracting later than the other.
Q-T interval
-period from the beginning of ventricular depolarization through repolarization and includes the time of ventricular contraction (S-T segment)
-Time required for the ventricles to undergo a single cycle of depolarization and repolarization
bradycardia
rate below 60 beats per minute
fibrillation
prolonged tachycardia leads to fibrillation. A condition of uncoordinated heart contractions which makes the heart useless as a pump. Uncoordinated myocardial activity.
stroke volume
amount of blood ejected by a ventricle with each contraction, increases with physical conditioning.
P wave
atrial depolarization
QRS complex
ventricle depolarization
T wave
ventricle repolarization
Intrinsic conduction system in order
SA node --> AV node --> AV bundle --> left and right bundle branches --> Purkinje fibers
At what structure in the transmission sequence is the impulse temporarily delayed? why?
AV node, because it allows for completion of atrial contraction between initiation of ventricular systole (contraction)
What is the role of the the nodal system?
it ensures that depolarization proceeds in order from atria to ventricles; and accelerates and coordinates heart activity to effectively pump blood.
Why does heart rate increase during running?
exercise raises heart rate through the sympathetic nervous system. Sympathetic nervous fibers release NE on the heart and the pacemaker fires more rapidly.
Immediately before P wave
the heart is in relaxation
During P wave
depolarization of the atria
Immediately after P wave, the P-R segment
contraction of the atria
during QRS complex
depolarization of ventricles
Immediately after QRS wave, the S-T segment
contraction of ventricles
during T wave
repolarization of ventricles
what would be more serious, an atrial or ventricular fibrillation? Why?
Ventricular fibrillation is more serious because the ventricles have major responsibility for pumping blood from the heart to the lungs and all other organs of the body.
Heart valve abnormalities can be detected by auscultation, not ECG. Why?
Valve problems are detected by stethoscope because they are not part of depolarization pathway of the heart, so an ECG would not be able to record changes.
SA node
pacemaker of heart, don't contract, but has pacemaker cells that automatically generates impulses to contract right atrium, generates impulses to AV node
AV node
pauses to allow completion of atrial contraction between initiation of ventricular systole (contraction). Sends impulse to AV bundle
AV bundle
connects the atria to the ventricles. Sends impulse to bundle branches.
bundle branches
conduct impulses through the interventricular septum
purkinje fibers
depolarize the contractile cells of both ventricles, causing the heart to beat.
stroke volume
the amount of blood ejected by a ventricle with each contraction. It can increase with physical conditioning.
"lub" sound
heard when AV valves close after ventricular depolarization
"dub" sound
heard when semilunar valves close from ventrical relaxation