Autorhythmic cells in the SA node intrinsically fire at a rate of - 90 action potentials per minute. At rest, the heart rate is lowered primarily through modulation by:O Decreased delivery of acetylcholine and increased delivery of norepinephrineIncreased delivery of acetylcholine and decreased delivery of norepinephrineCardiac contractile cellsDecreased delivery of acetylcholine and decreased delivery of norepinephrineIncreased delivery of acetylcholine and increased delivery of norepinephrineO O O

The heart is a major muscular organ of the cardiovascular system that is responsible for pumping the…

Answered: Autorhythmic cells in the SA node…

Human Anatomy & Physiology (11th Edition)

11th Edition

ISBN:9780134580999

Author:Elaine N. Marieb, Katja N. Hoehn

Publisher:Elaine N. Marieb, Katja N. Hoehn

Chapter1: The Human Body: An Orientation

Section: Chapter Questions

Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...

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In a cardiac contractile cell what is the mechanism involved in the change in membrane potential? Depolarization: P wave Repolarization: QRS Complex, Hyperpolarization: T wave Pacemaker: K+ and Na+ flow, Depolarization: Pca rises Repolarization: Pk rises Depolarization: Pna increases, Peak: Na channels close, Plateau: Calcium channels close & Potassium channels open, Repolarization Potassium flows out & Calcium flows in Pacemaker: K+ and Na+ flow, Depolarization: Pca rises Repolarization: Pk rises, 4. If channels close Depolarization: Pna increases, Peak: Na channels close, Plateau: Calcium channels open & Potassium channels close, Repolarization Potassium flows out & Calcium flows out
which of the following conditions at the S-A node will cause a decrease in heart rate? increased sodium permeability decreased acetylcholin levelsincreased norepinephrine levels increased potassium permeabilityincreased calcium permeability
The entry of calcium into a ventricular muscle cell helps to maintain depolarization of the membrane during the plateau phase of the action potential, but this calcium also performs what other function?
Describe the interactions of actin, myosin, and the troponin-tropomyosin complex in controlling heart function.
Which of the following combinations would have OPPOSITE effects in changing heart rate? atropine and norepinephrine atropine and a cholinesterase inhibitor epinephrine and norepinephrine acetylcholine and a cholinesterase inhibitor
Sympathetic stimulation increases the phosphorylation of the Ca2+ATPase in the sarcoplasmic reticulum. What effect does this have on cardiac function? It increases the rate of diastole It decreases the stretch of the ventricles The rate of systole decreases
The cardiac action potential is substantially longer than a neuron potential due to: spontaneous depolarization Ca++ entry gap junctions myocardial contractility
A 28-year-old athlete is noted to have a baseline heart rate of 55bpm, which his trainer attributes to excellent parasympathetic (vagal) tone. This parasympathetic effect normally increases Ach release at the SA and AV nodes. Ach release into AV node leads to which of the following effects of its fibers? a. increased action potential amplitudeb. increased conduction velocityc. increased K+ equilibrium potentiald. Hyperpolarizatione. increased rate of depolarization of the pacemaker potential
Which of the following statements best describes the differences in the regulation of cardiac and skeletal muscle contraction? The amount of contractile force actively generated by muscle cells is increased by stretch in skeletal muscle and decreased by stretch in cardiac muscle. Cardiac muscle is stimulated by motor neurons and skeletal muscle by neurones from the autonomic nervous system. Skeletal muscle contractile force is augmented by increasing the firing frequency of action potentials whereas cardiac muscle contractile force is enhanced by noradrenaline increasing calcium influx through ion channels. Ryanodine receptors in skeletal muscle are opened by a mechanism that requires calcium influx whereas in cardiac muscle membrane depolarisation alone without calcium influx is sufficient to open ryanodine receptors.
What is autorhythmicity? Describe how nodal cells function as autorhythmic cells to serve as the pacemaker of the heart.
Regarding the cardiac cycle at resting HR, when in the cycle does ventricular filling occur? Howimportant is atrial contraction to the EDV? Why is the first part of ventricular contraction isovolumetric?When and why does rapid ejection of blood from the ventricle occur?
Roberto is a 78-year-old male who has recently been diagnosed with Class III Congestive Heart Failure (CHF). His physician told him that his left ventricle has become stiff and cannot relax. Although there is no current treatment that can “fix” Roberto’s condition, he is prescribed two medications: an ACE inhibitor and beta blockers.Briefly describe how beta-blockers will influence Roberto’s heart function, specifically the physiology of the ventricles.

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