HW 7

Which cranial nerve provides roughly 75 percent of all parasympathetic outflow?

CN X

Which statement is correct regarding the intrinsic heart rate?

During parasympathetic stimulation, acetylcholine released by parasympathetic neurons opens chemically gated potassium channels in the plasma membrane.

In the sympathetic division of the ANS, the superior mesenteric ganglion innervates the

small intestine

The portion of the tracing of an electrocardiogram, ECG, that represents ventricular depolarization is the

QRS complex

Which part of the conduction system initiates the depolarizing impulse, which spreads throughout the heart?

SA node

Which part of the intrinsic conduction system normally initiates the depolarizing impulse that causes a heartbeat?

SA node

In an ECG recording, which of the following coincides with ventricular repolarization?

T wave

What statement is true regarding pressures and volumes in the cardiac ventricles?

The pressure is greater in the left ventricle, but the volumes are equal in the two chambers.

Calculate the cardiac output if heart rate (HR) is 90 beats per minute, stroke volume (SV) is 110 ml/beat, end diastolic volume (EDV) is 140 ml, and end systolic volume (ESV) is 30 ml.

9.9 L/min

Which of these structures conduct(s) action potentials the slowest?

AV node

Which part of the intrinsic conduction system delays the impulse briefly before it moves on to the ventricles?

AV node

Increased pressure in the ventricles would close what valve(s)?

AV valves only

What effect would an increase in venous return have on the stroke volume? (Module 18.15B)

An increase in venous return would fill the ventricles with more blood, increasing sarcomere length, which would increase the stroke volume.

Define heart failure

Heart failure is a condition where the heart can no longer meet the oxygen and nutrient demands of peripheral tissues.

Which of the following statements is correct concerning the cardiac cycle?

In late ventricular diastole, all chambers are relaxed and filling to about seventy percent of their capacity.

Which of the following is correct about the filling of the ventricles?

Most blood flows passively into the ventricles through open AV valves.

Contraction of the atria results from which wave of depolarization on the ECG tracing?

P wave

Describe the pressures in the atria and ventricles that would cause the opening of the AV valves.

Pressure in the atria would be greater than the pressure in the ventricles.

What structure carries the electrical signal from the septum of the heart through the ventricular myocardium?

Purkinje fibers

Which of the following would occur in a resting membrane after a stimulus is applied?

The opening of sodium channels will cause depolarization.

How would an increase in the sympathetic nervous system increase stroke volume?

increased contractility

What factor would decrease stroke volume?

an increase in afterload

What is the first phase of the cardiac cycle?

atrial systole

Which phase of the cardiac cycle is the shortest?

atrial systole

What electrolyte (ion) is responsible for the plateau in the cardiac action potential?

calcium

Stroke volume depends on all of the following except

cardiac output

Parasympathetic innervation of the lungs is via the

cardiac plexuses.

Which of the following is a sympathetic collateral ganglion?

celiac ganglion

The intrinsic eye muscles are the target organs of neurons from which parasympathetic ganglion?

ciliary ganglion

Which of the following is an effect of parasympathetic activation?

constriction of the pupils

An increase in sympathetic stimulation of the heart would increase stroke volume by increasing

contractility

How would a decrease in blood volume affect both stroke volume and cardiac output?

decreased stroke volume and no change in cardiac output (a decreased blood volume would decrease the end diastolic volume, thus lowering the stroke volume. Although this would initially lead to a decrease in the cardiac output, heart rate would increase because of increased activity of the sympathetic nervous system in an effort to maintain cardiac output.)

What does the ECG wave tracing represent?

electrical activity of the heart

The ________ is the volume of blood in a ventricle at the beginning of systole.

end-diastolic volume

Which of the following would increase heart rate?

epinephrine and norepinephrine

Averaged over a few heartbeats, venous return is ________ cardiac output.

equal to

When threshold is reached at the SA node (an autorhythmic cell), what channels open causing further depolarization of the membrane?

fast calcium

Action potentials generated by the autorhythmic cells spread to the contractile cells through what structures in the membrane?

gap junctions

What causes the aortic semilunar valve to close?

greater pressure in the aorta than in the left ventricle

Chemically gated channels:

include receptors that bind ACh at the neuromuscular junction.

What factor would increase heart rate?

increase in thyroxine (T4)

By what mechanism would an increase in venous return increase stroke volume?

increased end diastolic volume (an increase in venous return increases the end diastolic volume. The fibers are stretched more, resulting in an increase in the force of contraction (preload, or the Frank-Starling Mechanism).)

Which of the following would increase cardiac output to the greatest extent?

increased heart rate and increased stroke volume (cardiac output = heart rate x stroke volume)

Put the phases of the cardiac cycle in the correct order, starting after ventricular filling.

isovolumetric contraction, ventricular ejection, isovolumetric relaxation

Voltage-gated sodium channels are

open at -60 mV

One of the changes that occurs in the pacemaker potential (unstable resting membrane potential) in the SA node (an autorhythmic cell) is a decreased efflux of what ion?

potassium

The volume of blood ejected from each ventricle during a contraction is called the

stroke volume.

What structure prevents the electrical signals generated in the SA node from passing directly from the atrium through to the ventricles below?

the cardiac skeleton

A characteristic of graded potentials is

the effect spreads passively through local currents

In order to cause cardiac muscle contraction, the contractile cells must also depolarize. What causes the depolarization of the contractile cells?

the flow of positive ions from adjacent cells

What does the QRS complex represent in the ECG wave tracing?

ventricular depolarization

Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during

ventricular diastole

During which phase of the cardiac cycle is the blood pumped to the body?

ventricular systole

What event causes the closing of the AV valves, which results in the first heart sound?

ventricular systole

Isovolumetric contraction is associated with which cardiac cycle phase?

ventricular systole - first phase

Repolarization of an autorhythmic cell is due to the opening of which channels?

voltage-gated potassium channels