Physio Ch 10

Question 1

Under normal conditions, atria contract ___ ahead of ventricles

Answer 1

1/6 of a second

Question 2

conduct impulses from the sinus node to the atrioventricular (A-V) node

Answer 2

internodal pathways

Question 3

conducts impulses from the atria into the ventricles

Answer 3

A-V bundle

Question 4

conduct the cardiac impulses to all parts of the ventricles

Answer 4

right and left bundle branches of Purkinje fibers

Question 5

where impulses from the atria are delayed
before passing into the ventricles

Answer 5

AV node

Question 6

a small, flattened, ellipsoid strip of specialized cardiac muscle

Answer 6

SA node

Question 7

Located superior posterolateral wall of right atrium below and slightly lateral to the opening of the superior vena cava

Answer 7

SA node

Question 8

a process that can cause automatic rhythmical discharge and contraction

Answer 8

self-excitation

Question 9

resting membrane potential of the sinus nodal fiber between discharges

Answer 9

-55 to -60 mV

Question 10

RMP of ventricular muscle fiber

Answer 10

-85 to -90

Question 11

Why does SA node have lesser RMP or negativity?

Answer 11

Due to cell membrane’s natural leak to sodium and calcium ions (positive ions go inside the fibers)

Question 12

What are the 3 types of membrane ion channels present in the cardiac muscle?

Answer 12

(1) fast sodium channels
(2) slow sodium-calcium channels
(3) potassium channels

Question 13

Which channel is responsible for the rapid upstroke spike of the action potential observed in ventricular muscle

Answer 13

fast sodium channels

Question 14

Which channel is responsible for the plateau of the ventricular action potential

Answer 14

slow sodium-calcium channel

Question 15

Responsible for returning the cell membrane’s potential to its resting level

Answer 15

potassium channels

Question 16

resting potential of SA fibers gradually rises and becomes less negative between each ___ ?

Answer 16

2 heartbeats

Question 17

threshold voltage of SA fibers

Answer 17

-40 mV

Question 18

What is responsible for sinus nodal fibers self-excitation?

Answer 18

Inherent leakiness to sodium and calcium ions

Question 19

What are the 2 events that cause the sinus nodal fibers not remain depolarized all the time, despite its leakiness to sodium and calcium?

Answer 19

1. Sodium-calcium channels become inactivated within 100-150 secs after opening
2. Many potassium channels open

Question 20

Briefly summarize the process of self-excitation to re-excitation process of SA fibers.

Answer 20

1. self-excitation to cause the action
   potential
2. recovery from the action potential
3. hyperpolarization after the action potential is over
4. drift of the “resting” potential to threshold
5. re-excitation to elicit another cycle

Question 21

small bands of atrial fibers that passes through the anterior walls of the atria
to the left atrium

Answer 21

Anterior interatrial band

Question 22

What delays the transmission of conduction of the atria to the ventricles?

Answer 22

A-V node and adjacent conductive fibers

Question 23

located in the posterior wall of the right
atrium immediately behind the tricuspid valve

Answer 23

A-V node

Question 24

What causes the slow conduction in the transitional, nodal, and penetrating A-V bundle fibers?

Answer 24

diminished gap junctions

Question 25

transmit action potentials at a velocity of 1.5 to 4.0m/sec

Answer 25

Purkinje fibers

Question 26

What allows rapid transmission of action potentials by Purkinje fibers?

Answer 26

High permeability of gap junctions at the intercalated discs

Question 27

acts as an insulator to prevent passage of
the cardiac impulse between atrial and ventricular muscle through any other route besides forward conduction through the A-V bundle itself

Answer 27

continuous fibrous barrier

Question 28

discharge at an intrinsic rhythmical rate
of 40 to 60 times per minute when not stimulated from outside source

Answer 28

A-V nodal fibers

Question 29

Why does the sinus node rather than the A-V
node or the Purkinje fibers control the heart’s rhythmicity?

Answer 29

Discharge rate of the sinus node is considerably faster than the natural self-excitatory discharge rate of either the A-V node or the Purkinje fibers.

Question 30

its rate of rhythmical discharge is faster than
that of any other part of the heart

Answer 30

SA node

Question 31

What is an ectopic pacemaker?

Answer 31

A pacemaker elsewhere than the sinus node

Question 32

responsible for abnormal sequence of contraction of the different parts of the heart and can cause significant debility of heart pumping

Answer 32

ectopic pacemaker

Question 33

delayed pickup of the heartbeat due to A-V block

Answer 33

Stroke-Adams syndrome

Question 34

What are the 2 major effects of acetylcholine released on the vagal endings to the heart?

Answer 34

1. Decreases rate of rhythm of the sinus node
2. Decreases the excitability of the A-V junctional fibers between the atrial musculature and the A-V node

Question 35

It is when vagi stops or block the transmission of cardiac impulse from atria to ventricles, but some areas of Purkinje fibers develops a rhythm of its own and causes ventricular contraction

Answer 35

Ventricular escape

Question 36

Effect of Sympathetic Stimulation on Cardiac Rhythm and Conduction (3)

Answer 36

1. Increases the rate of sinus nodal discharge
2. Increases the rate of conduction and level of excitability
3. Increases the force of contractions of all the cardiac musculature

Question 37

hormone released by sympathetic nerves to increase the overall activity of the heart

Answer 37

norepinephrine