Exam 2 – Cardio Ch 10

Question 1

What is the pathway of the heartbeat?

Answer 1

Begins in the sinoatrial (SA) node
Internodal pathway to atrioventricular (AV) node
Impulse delayed in AV node
AV bundle takes impulse into ventricles
Left and right bundle branches of Purkinje fibers take impulses to all parts of ventricles

Question 2

What is the importance of the delay in AV nodes?

Answer 2

Allows atria to contract before ventricles

Question 3

What are conduction fibers?

Answer 3

Modified cardiomyocytes

Question 4

Do conduction fibers contract?

Answer 4

Yes, just not as much

Question 5

What is the function of the conduction system?

Answer 5

Conduct depolarization quickly to all parts of myocardium

Question 6

What is the sinus node?

Answer 6

Specialized cardiac muscle connected to atrial muscle

Question 7

What does the sinus node act as?

Answer 7

Pacemaker

Question 8

Why does sinus node act as a pacemaker?

Answer 8

Because membrane leaks Na+ into cell and resting membrane potential is -55 to -60mV
SELF-EXCITATORY

Question 9

What happens when membrane potential reaches -40mV in sinus node?

Answer 9

Slow Ca++ channels open causing action potential

After 100-150 msec, Ca++ channels close

Question 10

What happens when Ca++ channels close in sinus node action potential?

Answer 10

K+ channels open more thus returning membrane potential to -55mV

Question 11

LOOK AT RHYTHMICAL DISCHARGE OF SINUS NODAL FIBER CHART

Answer 11

LOOK AT RHYTHMICAL DISCHARGE OF SINUS NODAL FIBER CHART

Question 12

What do the internodal pathways transmit?

Answer 12

Cardiac impulses throughout atria

Question 13

What are the 3 internodal pathways?

Answer 13

Anterior
Middle
Posterior

Question 14

What does the anterior interatrial band of the internodal pathway carry?

Answer 14

Impulses to left atrium

reaches AV node in 0.03 seconds

Question 15

What does the AV node delay?

Answer 15

Cardiac impulses
slows down to make sure ventricles are behind atria at a good speed
Delay allows time for atria to empty its blood into ventricles before ventricular contraction begins

Question 16

Where is the delay located?

Answer 16

AV node

Question 17

What is the delay in the AV node?

Answer 17

0.09 sec

Question 18

What is the delay in the AV bundle?

Answer 18

0.04 sec

Question 19

Define the atrial conductive system

Answer 19

Organized so that the cardiac impulse does not travel from the atria into ventricles too rapidly

Question 20

What is the Purkinje system?

Answer 20

Fibers lead from AV node through AV bundle into ventricles

Question 21

What speed conduction does the purkinje system have?

Answer 21

Fast due to many gap junctions at intercalated discs
Fast conduction allows almost instantaneous transmission of the cardiac impulse throughout entire remainder of cardiac impulse

Question 22

How do the gap junctions in the purkinje system contribute to fast conduction?

Answer 22

Rapid transmission caused by high level of permeability of gap junctions at intercalated discs between successive cells that make up purkinje fibers

Question 23

What is the direction of conduction in AV bundles?

Answer 23

One way conduction through bundles

Question 24

What is the only conducting path between atria and ventricles?

Answer 24

AV node-AV bundle

divides into left and right bundles

Question 25

What is the importance of one way conduction in AV bundles?

Answer 25

Inability of action potentials to travel backwards from ventricles to atria Prevents re-entry of cardiac impulses Forward conduction

Question 26

What is the transmission time between AV bundles and last of ventricular fibers?

Answer 26

0.06 seconds | QRS time

Question 27

What is the normal rate of discharge in sinus node?

Answer 27

70-80/min

Question 28

What is the normal rate of discharge in AV node?

Answer 28

40-60/min

Question 29

What is the normal rate of discharge in Purkinje fibers?

Answer 29

15-40/min

Question 30

Why is the sinus node the pacemaker of the heart?

Answer 30

Because of its faster discharge rate | Sets tone of the heartbeat for AV nodes and Purkinje fibers

Question 31

Why are the sinus nodes self excitatory?

Answer 31

Conduction system is very leaky and builds up a potential

Question 32

What is the most important function of the AV node?

Answer 32

It can take over the beating of the heart if the sinus node fails Keeps animal alive

Question 33

Why can the AV node and Purkinje fibers not self-excite?

Answer 33

The sinus node discharges so too fast

Question 34

What is an ectopic pacemaker?

Answer 34

Portion of heart with a more rapid discharge than sinus node also occurs when transmission from sinus node through AV node is blocked (AV block)

Question 35

What does an ectopic pacemaker cause?

Answer 35

Abnormal sequence of contraction of different parts of heart and can cause significant debility of heat pumping

Question 36

What becomes pacemaker of heart during sudden onset of AV block when sinus node discharge does not get through?

Answer 36

Purkinje system

Question 37

What is Stokes-Adams syndrome?

Answer 37

Delay in pickup of heat beat New pacemaker is AV node or penetrating part of AV bundle When no contractions are occurring while waiting on another pacemaker to take over

Question 38

What happens if the heart doesn't beat for 4 seconds?

Answer 38

Pass out | Could lead to death

Question 39

What are the parasympathetic effects on heart rate?

Answer 39

Parasympathetic (vagal) nerves, which release acetylcholine at their endings, innervate SA node and AV junctional fiber proximal to AV node causes hyperpolarization

Question 40

What causes hyperpolarization due to parasympathetic effects?

Answer 40

Increased K+ permeability in response to acetylcholine This causes decreased transmission of impulses which may temporarily stop heart rate Ventricular escape occurs

Question 41

What is acetylcholine affects on the heart?

Answer 41

Decreased rate of rhythm of sinus node Decreased excitability of AV junctional fibes between atrial musculature and AV node, which slows transmission of cardiac impulse into ventricles

Question 42

What are the sympathetic effects on heart rate?

Answer 42

Releases norephinephrine at sympathetic endings Causes increased sinus node discharge Increased rate of conduction of impulse Increases force of contraction in atria and ventricles