Pacemaker cells trigger action potentials throughout the heart

Question 1

Although the ability of the heart to depolarize and contract _________ the healthy heart is supplied with
__________ that alter its basic rhythrn.

Answer 1

intrinsic

autonomic nerve fibers

Question 2

The independent, but coordinated, activity of the heart is a function of 2 things what are they

Answer 2

1) the gap junctions

2) the in house conduction system

Question 3

consists of noncontractile cardiac cells specialized to initiate and distribute impulses throughout the heart, so that it depolarizes and contracts in an orderly, sequential manner

Answer 3

the intrinsic cardiac conduction system

Question 4

However, about 1 % of cardiac fibers are autorhythmic

Answer 4

pacemaker cells

Question 5

having the special ability to depolarize spontaneously and so pace the heart

Answer 5

pacemaker cells

Question 6

Pacemaker cells are a part of the ________. They have an ______ resting potential that continuously _______, drifting slowly toward threshold.

Answer 6

intrinsic conduction system
unstable
depolarizes

Question 7

These spontaneously changing membrane potentials, called __________ or _______ initiate the action potentials that spread throughout the heart to trigger its rhythmic contractions.

Answer 7

pacemaker potentials

prepotentials

Question 8

The pacemaker potential is due to the

special properties of the

Answer 8

ion channels in the sarcolemma

Question 9

This slow depolarization is due to both opening of Na’ channels and closing of K’ channels. Notice that the membrane potential is
never a flat line.

Answer 9

pacemaker potential

Question 10

The action potential begins when
the pacemaker potential reaches threshold.
Depolarization is due to Ca2+ influx through Ca2+
channels.

Answer 10

depolarization

Question 11

is due to Ca2+ channels inactivating
and K’ channels opening. This allows K’ efflux, which
brings the membrane potential back to its most
negative voltage.

Answer 11

repolarization

Question 12

Once repolarization is complete, K+ channels ____, K+ efflux ____, and the slow _____ to threshold begins again.

Answer 12

close
declines
depolarization

Question 13

typical cardiac pacemaker cells are found in the

Answer 13

sinoatrial and atrioventricular nodes

Question 14

list the 5 stages of the The intrinsic cardiac conduction system

Answer 14

1) sinoatrial (AV) node
2) Atrioventricular (AV) node
3) Atrioventriuclar (AV) bundle
4) Right and left bundle branches
5) Subendocardial conducting network.

Question 15

sinoatrial node impulse

Answer 15

75 times / minute

Question 16

the sinoatrial node is the hearts’ ________ and its characteristic rhythm, called _________, determines _______.

Answer 16

pacemaker
sinus rhythm
heart rate

Question 17

From the SA node, the depolarization wave spreads via _______ throughout the atria and via the _________ to the ______, located in the inferior portion of the interatrial septum immediately above the tricuspid valve.

Answer 17

gap junctions
internodal pathway
AV node

Question 18

At the AV node, the impulse is __________ allowing the atria to respond and complete their
contraction before the ventricles contract

Answer 18

delayed for about 0.1 second

Question 19

the 0.1 second delay at the AV node reflects what

Answer 19

the smaller diameter of the fibers and the fact that they

have fewer gap junctions for current flow.

Question 20

the AV node conducts impulses ________ than other parts of the system

Answer 20

more slowly

Question 21

From the AV node, the impulse sweeps to the

Answer 21

atrioventricular bundle (also called the bundle
of His)

Question 22

Although the atria and ventricles are adjacent to each other, they are not connected by

Answer 22

gap junctions

Question 23

what is the only electrical connection between the atria and the ventricles

Answer 23

the AV bundle

Question 24

The fibrous cardiac skeleton is nonconducting and

Answer 24

insulates the rest of the AV junction

Question 25

The short

AV bundle splits into two pathway

Answer 25

right and left bundle branches

Question 26

the right and left bundle branches go from

Answer 26

interventricular septum towards the heart apex

Question 27

Essentially long strands of barrel-shaped cells with few myofibrils, the __________-, also called ___________ completes the pathway through the interventricular septurm, penetrates into the heart apex, and then turns superiorly into the ventricular walls

Answer 27

subendocardial conducting network

purkinje fibers

Question 28

The SA node normally drives the
heart at a rate of ___ beats per minute. Without SA node input, the AV node would depolarize only about ___ times per minute.
Without input from the AV node, the atypical pacemakers of the
AV bundle and the subendocardial conducting network would
depolarize only about ___ times per minute.

Answer 28

75
50
30

Question 29

which center projects to the sympathetic neurons

Answer 29

cardioacceleratory center

Question 30

which center projects to the parasympathetic dorsal vagus nucleus in the medulla

Answer 30

cardioinhibitory center

Question 31

is due to Na+ influx through fast
voltage-gated Na+ channels. A positive feedback cycle
rapidly opens many Na+ channels, reversing the
membrane potential . Channel inactivation ends this
phase

Answer 31

depolarization

Question 32

is due to Ca2+ influx through slow
Ca2+ channels. This keeps the cell depolarized because
most K+ channels are closed.

Answer 32

Plateau phase

Question 33

is due to Ca2+ channels inactivating
and K+ channels opening. This allows K+ efflux, which
brings the membrane potential back to its resting
voltage.

Answer 33

Repolarization

Question 34

in cardiac muscle, the action potential lasts 200 rns or more because of the

Answer 34

Plateau phase

Question 35

This long plateau in cardiac muscle has two

consequences:

Answer 35

• It ensures that the contraction is sustained so that blood is ejected efficiently from the heart.
• It ensures that there is a long absolute refractory period, so that tetanic contractions cannot occur and the heart can fill again for the next beat.

Question 36

The first, the _____, lasts about ___ s and results from movement of the depolarization wave from the _____ through the ___. Approximately ___ s after the P wave begins, the ____contract.

Answer 36

small P wave
0.08
SA node
atria
0.1
atria

Question 37

Atrial depolarization, initiated by

the SA node, causes the

Answer 37

P wave

Question 38

The large _____ results from ________ and precedes ventricular contraction. It has a complicated shape
because the paths of the depolarization waves through the ventricular walls change continuously, producing corresponding changes in current direction. Additionally, the time required for each ventricle to depolarize depends on its size relative to the other ventricle. Average duration of the QRS complex is ___s.

Answer 38

QRS complex
ventricular depolarization
0.08

Question 39

Ventricular depolarization begins at ___, causing the _________. _________ occurs.

Answer 39

apex
QRS complex
Atrial repolarization

Question 40

The T wave, caused by ________, typically lasts about 0.16 s. Repolarization is ____ than depolarization, so the T wave is more ________and has a lower amplitude (height) than the QRS complex. Because atrial repolarization takes place during the period of ventricular excitation, the wave representing atrial repolarization is normally obscured by the large ______ being recorded at the same time.

Answer 40

ventricular repolarization
slower
spread out
QRS complex

Question 41

The P-R interval is the time (about 0.16 s) from the _____ to the _____. If the Q wave is visible, it marks the beginning of ______, and for this reason this interval is sometimes called the _____. The P-R interval includes_____ as well as the passage of the ______ through the rest of the conduction system.

Answer 41

beginning of atrial excitation 
beginning of ventricular excitation
ventricular excitation
PQ interval
atrial depolarization
depolarization wave

Question 42

Ventricular repolarization begins at

___, causing the _____

Answer 42

apex

T wave

Question 43

During the ______ of the ECG, when the action potentials of the ventricular myocytes are in their _____, the entire ventricular myocardium is depolarized. The _________, lasting about 0.38 s, is the period from the ________ through _________

Answer 43

S-T segment
plateau phases
Q-T interval
beginning of ventricular depolarization
ventricular repolarization