Answers Lab06 ECG
M31_MARI0000_00_SE_CH31.qxd
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R E V I E W
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S H E E T
NAME ____________________________________
EXERCISE
LAB TIME/DATE _______________________
Conduction System of the Heart and
Electrocardiography
The Intrinsic Conduction System
1. List the elements of the intrinsic conduction system in order, starting from the SA node.
SA node → AV node
→ AV bundle (bundle of His)
→
→ Purkinje fibers
left and right bundle branches
At what structure in the transmission sequence is the impulse temporarily delayed? AV node
Why? Allows completion of atrial contraction before initiation of ventricular systole.
2. Even though cardiac muscle has an inherent ability to beat, the nodal system plays a critical role in heart physiology. What is that role? Ensures that depolarization proceeds in an orderly manner from atria to ventricles; accelerates and coordinates heart activity to effectively pump blood.
Electrocardiography
3. Define ECG. Recording of electrical changes occurring during heart activity.
4. Draw an ECG wave form representing one heartbeat. Label the P, QRS, and T waves; the P-R interval; the S-T segment; and the Q–T interval.
R
S-T segment
T
P
Q
P-R interval
S
Q-T interval
5. Why does heart rate increase during running? Exercise raises heart rate by acting through the sympathetic nervous system.
Sympathetic nerve fibers release norepinephrine on the heart and the pacemaker fires more rapidly.
196
Copyright © 2011 Pearson Education, Inc.
M31_MARI0000_00_SE_CH31.qxd
3/29/11
4:45 PM
Page 197
6. Describe what happens in the cardiac cycle in the following situations.
1.
immediately before the P wave: the heart is in relaxation (diastole)
2.
during the P wave: depolarization of the atria
3.
immediately after the P wave (P-R segment): contraction of the atria
4.
during the QRS wave: depolarization of the ventricles
5.
immediately after the QRS wave (S-T interval): contraction of the ventricles
6.
during the T wave:
31
3/29/11
4:45 PM
R E V I E W
Page 196
S H E E T
NAME ____________________________________
EXERCISE
LAB TIME/DATE _______________________
Conduction System of the Heart and
Electrocardiography
The Intrinsic Conduction System
1. List the elements of the intrinsic conduction system in order, starting from the SA node.
SA node → AV node
→ AV bundle (bundle of His)
→
→ Purkinje fibers
left and right bundle branches
At what structure in the transmission sequence is the impulse temporarily delayed? AV node
Why? Allows completion of atrial contraction before initiation of ventricular systole.
2. Even though cardiac muscle has an inherent ability to beat, the nodal system plays a critical role in heart physiology. What is that role? Ensures that depolarization proceeds in an orderly manner from atria to ventricles; accelerates and coordinates heart activity to effectively pump blood.
Electrocardiography
3. Define ECG. Recording of electrical changes occurring during heart activity.
4. Draw an ECG wave form representing one heartbeat. Label the P, QRS, and T waves; the P-R interval; the S-T segment; and the Q–T interval.
R
S-T segment
T
P
Q
P-R interval
S
Q-T interval
5. Why does heart rate increase during running? Exercise raises heart rate by acting through the sympathetic nervous system.
Sympathetic nerve fibers release norepinephrine on the heart and the pacemaker fires more rapidly.
196
Copyright © 2011 Pearson Education, Inc.
M31_MARI0000_00_SE_CH31.qxd
3/29/11
4:45 PM
Page 197
6. Describe what happens in the cardiac cycle in the following situations.
1.
immediately before the P wave: the heart is in relaxation (diastole)
2.
during the P wave: depolarization of the atria
3.
immediately after the P wave (P-R segment): contraction of the atria
4.
during the QRS wave: depolarization of the ventricles
5.
immediately after the QRS wave (S-T interval): contraction of the ventricles
6.
during the T wave: