Ch. 20 Group 2

Although tetanus in skeletal muscle is a desirable characteristic, why is it important that cardiac muscle cannot be tetanized?

A heart in tetany cannot pump blood.

Why can't the heart be tetanized like skeletal muscle?

Cardiac muscle has a long absolute refractory period.

What ion movement is responsible for the rapid depolarization phase of the ventricular muscle cell action potential?

Na+ inflow

What is the correct sequential path of a normal action potential in the heart?

SA node, AV node, bundle AV, bundle branches, Purkinje fibers

Which of the following is/are called the cardiac pacemaker?

Sinoatrial node

Why is it important for impulses from the atria to be delayed at the AV node before they pass into the ventricles?

So the ventricles can finish filling

Which of the following are characteristics of cardiac muscle cells?

Striated, single central nucleus, and involuntary

On an ECG, which electrical feature accompanies repolarization of the ventricles?

T wave

Which of the following events does NOT occur because of the QRS wave?

The AV valves open.

If cells of the SA node did NOT function, what would happen to the heart?

The heart would beat more slowly.

On an ECG, a P-R interval longer than 200 msec would indicate ________________ .

damage to the AV node or internodal pathways

The passageways between cardiac muscle cells that allow ions to pass freely are called __________.

gap junctions

Cardiac muscle tissue __________.

has its own intrinsic conduction system to set the pace of the beating heart

The SA node, AV node, AV bundle (of His), and the Purkinje fibers are all components of the _____________ .

heart's conducting system

Atrial cells, and then ventricular cells, contract together as a unit refered to as a functional syncytium. This coordinated contraction is facilitated by specialized structures called ________________ .

intercalated discs

Following cardiac muscle depolarization, there is a period of time during which a cell cannot respond to a second stimulus. This time is referred to as the __________.

refractory period

Increased sympathetic stimulation to the heart might result in a situation known as _______.

tachycardia

On an ECG, which electrical feature accompanies depolarization of the atria?

P wave

What structures in the conduction system conduct impulses very rapidly to the ventricular myocardium?

Purkinje fibers

Why are the SA node cells autorhythmic?

They have a slow inflow of Na+ after repolarization.

Which of the following is NOT a characteristic of cardiac muscle cells?

They have multiple nuclei.

The QRS complex of the ECG appears as the __________.

ventricles depolarize

The QRS complex on the ECG represents __________.

ventricular depolarization