PCB4708L 06-02

Which branch of the ANS is more active at rest?

Parasympathetic

Vagal escape probably involves a. parasympathetic reflexes b. vagus nerves c. sympathetic reflexes d. cranial reflexes

c. sympathetic reflexes

Why is the SA node the pacemaker?

it has the fastest rate of spontaneous depolarization, and thus, determines the HR

Vagus nerve

the tenth cranial nerve that innervates digestive organs, heart and other areas

CN X

vagus nerve

What nerve carries the signal to the heart?

vagus nerve (CNX)

What do you think would happen to the heart rate if the vagus nerve was cut?

vagus nerve decreases heart rate so cutting it would increase heart rate.

What can vagal escape be the result of?

-sympathetic reflexes -initiation of a rhythm by the purkinje fibers

The SA node generates how many AP's per minute in the absence of PSN + SNS stimulation and hormonal controls?

100

Effect of PNS on the heart

Decreases the heart rate without directly changing the force of contraction

Explain the effect that extreme vagus nerve stimulation had on the heart.

Extreme vagus nerve stimulation decreases heart rate until the heart completely stops.

What happens when the stimulation of the vagus nerve is excessive?

Heart will stop beating and after a short time the ventricles will begin to beat again.

Effect of SNS on the heart

Increases rate and force of contraction of the heart

What is the pacemaker of the heart?

SA node

What are the branches of the autonomic nervous system?

Systemic and parasympathetic

Describe how the sympathetic and parasympathetic nervous systems work together to regulate heart rate.

The sympathetic nervous system increases heart rate while the parasympathetic decreases heart rate.

The effect of the parasympathetic nervous system on the heart is to a. decrease the heart rate b. decrease the heart rate and decrease the force of contraction c. increase the heart rate d. increase the heart rate and increase the force of contraction

a. decrease the heart rate

The vagus nerve carries a. signals that decrease the heart rate b. signals that decrease the heart rate and the force of contraction of the heart c. signals that decrease and increase the heart rate d. signals that increase the heart rate and increase the force of contraction of the heart

a. signals that decrease the heart rate

Extreme vagus nerve stimulation affects the heart by a. stopping the heart completely b. increasing the heart rate c. decreasing the heart rate d. decreasing the force of contraction of the heart

a. stopping the heart completely

Research shows that, in the absence of neural and hormonal influences, the SA node generates action potentials at a frequency of approximately 100 times per minute. However, the resting heart rate is approximately 70 beats per minute, which suggests that a. the sympathetic nervous system has more control over heart rate b. the parasympathetic nervous system has more control over heart rate c. the heart is undergoing vagal escape d. the heart is not autorhythmic

b. the parasympathetic nervous system has more control over heart rate

The branch of the autonomic nervous system that dominates during exercise is a. the parasympathetic branch b. the sympathetic branch c. neither the parasympathetic nor the sympathetic branch d. both branches

b. the sympathetic branch

Explain two ways that the heart can overcome excessive vagal stimulation.

by initiating rhythm of heart beat by purkinje fibers and sympathetic reflexes

The SA node in the human heart is located a. in the purkinje fibers b. in the left ventricle c. in the right atrium d. in the left atrium

c. in the right atrium

The usual pacemaker of the heart a. is always external b. is the Purkinje fibers c. is the sinoatrial node d. requires input form the nervous system

c. is the sinoatrial node

SA node

cluster of autorhythmic cardiac cells in the right atrial wall

Parasympathetic stimulation reaches the heart through a. peripheral nerves b. motor nerves c. sensor nerves d. vagus nerves, which are cranial nerves

d. vagus nerves, which are cranial nerves

Vagal escape

resumption of the heartbeat