EBK BIOLOGY
11th Edition
ISBN: 8220102797352
Author: Raven
Publisher: YUZU
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Textbook Question
Chapter 49, Problem 1A
In vertebrate hearts, atria contract from the top, and ventricles contract from the bottom. How is this accomplished?
a. Depolarization from the SA node proceeds across the atria from the top; depolarization from the AV node is carried to the bottom of the ventricles before it emanates over ventricular tissue.
b. The depolarization from the SA node is initiated from motor neurons coming down from our brain; depolarization from the AV node is initiated from motor neurons coming up from our spinal cord.
c. Gravity carries the depolarization from the SA node down from the top of the heart; contraction of the diaphragm forces depolarization from the AV node from the bottom up.
d. This statement is false; both contract from the bottom.
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Why is it necessary to stimulate papillary muscles in the ventricle slightly earlier than the rest of the ventricular wall myocardium?
a. to assure rapid conduction speed of the action potential
b. to pull on AV valve cusps to prevent backflow
c. to assure blood will surge toward the semilunar valves
d. to assure coordinated contraction of the ventricular myocardium
SA node is the main pacemaker of the heart. Why is the normal heart rate lower than the intrinsic firing rate of the SA node?
A. sympathetic inputs from the hypothalamus are slowing it down
B. parasympathetic inputs from medulla oblongata are slowing it down
C. there is inertia in heart muscle as it takes time for impulse to spread through all the cells
D. centrifugal inputs from the AV node are slowing it down
What is the consequence of the prolonged plateau of depolarization in ventricular myocytes?
a-it causes ventricular myocytes to contract for a longer time, allowing the ventricles time to empty
b-it gives additional time for the atria to contract, filling the ventricles more completely
c-it causes repolarization to be delayed which slows heart rate
d-it allows the ventricles a moment to rest before completing contraction
Chapter 49 Solutions
EBK BIOLOGY
Ch. 49 - An ECG measures a. changes in electrical potential...Ch. 49 - Systole is vitally important to heart function and...Ch. 49 - Which of the following is the correct sequence of...Ch. 49 - Which of the following statements is not true? a....Ch. 49 - Prob. 5UCh. 49 - Prob. 6UCh. 49 - When a sphygmomanometer is used, a. blood pulses...Ch. 49 - Prob. 8UCh. 49 - In vertebrate hearts, atria contract from the top,...Ch. 49 - Prob. 2A
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