Blake_Physio_07_Heart Rhythmicity

Question 1

SA node: definition, loccation and connections

Answer 1

Sinoatrial Node
Special Cardiac Muscle Fibers
SA fibers connect directly to atrial fibers

Question 2

AV node: definition
Receives signal ______ sec after origin
Signal is delayed in AV node for ________ sec
final delay of ____ sec in penetrating bundles
=> there is a ____sec delay from the initial origin of the isgnal until the onset of ventricular contraction

Answer 2

Atrioventricular Node

0. 03
1. 09
2. 04
3. 16

Question 3

Why is signal delayed in the AV node for 0.09 sec?

Answer 3

Due to the small size of cells, low amplitude of AP, and slow rate of depolarization during excitation.

Question 4

CONDUCTIVE SYSTEM OF THE HEART:
Slow conduction is caused mainly by diminished numbers of _____________ along the pathway resulting in an _____________ in the __________ to ___________

Answer 4

Gap junctions
increase
resisitance
conduction

Question 5

Resting membrane potential of SA node fiber:

Answer 5

-55 to -60mV (threshhold~-40mV)

Question 6

At resting potential, the Fast sodium channels in the SA node are____________

Answer 6

inactivated

Question 7

Inactivation gates close when the membrane potential of the SA node is __________________.

As a result, only ______ ______-_____ channels can open.

THEREFORE: (2 things)

Answer 7

less than -55mV

slow sodium-calcium

• atrial nodal AP is slower to develop
• repolarization is slower

Question 8

What causes the SA node to reach threshold on its own?

Answer 8

slow leak of sodium Ions back into cells

Question 9

Sodium-calcium channels in the SA node are inactivated within _____ to _______ msec after opening

Answer 9

100-150

Question 10

Resting membrane potential of SA node fiber:
Large numbers of _________ channels open at the time the __________-________ channels become ________

Nodal cells become ____________

Potassium channels remain __________ for a few tenths of a second

Answer 10

potasium, sodium-calcium, inactivated

repolarized

open

Question 11

Ventricular fiber resting potential:

Answer 11

=85 to -90mV

Question 12

Sinus Rhythm

Answer 12

AP originating in the SA node

Question 13

Action potentials that originate anywhere other than the SA node are said to be from an ________ or ________

Answer 13

ectopic focus or pacemaker

Question 14

What parasympathetic nerve can modulate heart rate?

What result does parasympathetic innervation have on the heart?

Answer 14

Vagus nerve

Decreased heart rate

Question 15

What receptors does acetylcholine affect on the heart?

Answer 15

• Muscarinic receptors on the SA and AV nodes

Question 16

What effect does acetylcholine have on the SA node?

Answer 16

decreases rate of rhythm (negative chronotropic effect)

Question 17

What effect does acetylcholine have on the AV node?

Answer 17

Decreases excitability of the AV junctional fibers, slowing transmission of the cardiac impulse into the ventricles.

Question 18

How does acytlycholine generally accomplish it’s functions in cardiac tissues? (2 things)

Answer 18

• Increases permeability of fiber membranes to potassium ions
• Hyperpolarization: -65 to -70mV

Question 19

How does sympathetic innervation by norepiniphrine effect cardiac tissue? (3 things)

Answer 19

• stimulates beta-1 adrenergic receptors
• increases depolarization rate (positive chronotropic effect)
• may increase permeability of fiber membranes to sodium and calcium ions

Question 20

Where is norepinephrine distributed to the heart by sympathetic nerves?

Answer 20

All parts of the heart, mainly the ventricles.

Question 21

In an ECG Depolarization is represented by the_ _ _

Answer 21

P and QRS waves

Question 22

ECG: P wave represents

QRS wave represents

T wave represents

Answer 22

Atrial depolarization

Ventricular depolarization

Ventricular repolarization

Question 23

In an ECG, why is there no wave representing Atrial repolarization?

Answer 23

because it is obscured by the QRS wave

Question 24

An ECG measures ______________

Answer 24

Extracellular potential

Question 25

Deflection from 0 occurs only when there is __________ between regions of the heart. Current flows between ________ of different _____________.

Answer 25

current flow regions membrane potentials

Question 26

Because atrial musculature and ventricular musculature are _________ _________, current flow does not occur when only the ________ and the _______ have different _______.

Answer 26

electrically isolated atria ventricals potentials

Question 27

Monophasic action potential of the ventricular muscle:

Answer 27

Depolarization and Repolarization both register as positive.

Question 28

in an ECG, no potential is recorded when the ventrical is:

Answer 28

completely polarized | completely depolarized

Question 29

Normal ECG: P wave occurs at the beginning of the contraction of the ______. QRS complex occurs at the beginning of the contraction of the __________. Repolarization of the _______ occurs after the end of the _______.

Answer 29

atria ventricals ventricals T-wave

Question 30

how long is the P-Q interval?

Answer 30

0.16 sec

Question 31

How long is the Q-T interval?

Answer 31

0.35 sec

Question 32

Three bipolar limb leads: I II III

Answer 32

I - neg to R-arm; pos to L-arm; Left to Right II - neg to R-arm; pos to L-leg; upper right to lower left III - neg to L-arm; pos to L-leg; upper left to lower left

Question 33

Two arms and left leg form ________ triangle

Answer 33

Einthoven's

Question 34

Einthoven's law:

Answer 34

If the electrical potentials of any two of the three bipolar limb leads are known at any givan instant, the third can be determined by summing the first two.

Question 35

Normally, in the ventricals, current flows from ______ to the ________ in the direction of the _______ of the heart to the _________ for most of the heart cycle until the very end.

Answer 35

negative to positive | base to apex

Question 36

Axis for ECG bipolar limb leads: I II III

Answer 36

I - 0 II - 60 III - 120

Question 37

The QRS vector: name and angle

Answer 37

mean electrical axis | 59 degrees

Question 38

T-Wave: Greatest portion of ventricular mass to repolarize first is the entire_____________ of the _________, especially near the _________.

Answer 38

outer surface ventricles apex

Question 39

T-Wave: | Endo cardial areas normally repolarize ________

Answer 39

last

Question 40

T-wave: | Ventricular vector during repolarization is toward the ______ of the _________

Answer 40

apex of the heart

Question 41

T-wave: | Normal T-wave in all three bipolar leads is ________

Answer 41

positive

Question 42

P-wave: | Atrial depolarization begins in the ________

Answer 42

Sinus Node

Question 43

P-wave: | Vector direction is generally in the ________of the axes of the three standard bipolar limb leads.

Answer 43

same direction

Question 44

P-wave: | ECG of P-wave is normally _______ in all three leads

Answer 44

positive

Question 45

Atrial T-wave: | Spread of depolarization through atrial muscle is ________ than in ____________

Answer 45

slower than in ventricles

Question 46

Atrial T-wave: Musculature around the sinus node becomes __________ a long time _______ the musculature in the distal parts of the atria.

Answer 46

depolarized | before

Question 47

Atrial T-wave: | The ___________ area is the first part to become repolarized.

Answer 47

sinus node

Question 48

Atrial T-wave: | At the beginning of repolarization, the sinus node is ___________ with respect to the rest of the atria.

Answer 48

positive

Question 49

Atrial T-wave: | Atrial T-wave is almost always ________ by the QRS wave.

Answer 49

obscured

Question 50

A typical ECG may utilize ___ leads. Each lead provides a _______ _______ on the _____ _________ between areas of the heart. In addition to the three bipolar (conventional leads) there are:

Answer 50

12 different perspective voltage difference 6 standard leads (V1-V6) Three augmented Leads (aVR, aVL, aVF)

Question 51

The mean electrical axis is the direction of _________________ from the __________ to the _______

Answer 51

electrical potential | base of the ventricals to the apex

Question 52

5 abnormal ventricular conditions that cause axis deviation:

Answer 52

- Change in position of the heart in the chest - hypertrophy of one ventrical - bundle branch block - fluid in pericardium - pulmonary emphysema

Question 53

Abnormal Voltages of QRS complex: In creased voltage in the standard bipolar leads: (2 things) (1 measurement, 1 cause)

Answer 53

- High-voltage ECG is said to occur when the sum of the voltages of all QRS complexes of the three standard leads is greater than 4mV. - Most common cause is hypertrophy of the ventricle.

Question 54

Abnormal Voltages of QRS complex: | Decreased Voltage: (2 causes)

Answer 54

cardiac myopathies | conditions surrounding the heart

Question 55

Hypertrophy or dilation of the left or right ventricle, QRS may be prolonged to _____ to _____ sec

Answer 55

0.09 to 0.12 sec

Question 56

Conditions causing bizarre QRS complexes:

Answer 56

- Destruction of cardiac muscle and replacement by scar tissue. - Multiple small local blocks in the conduction impulses at many points in the Purkinje system.

Question 57

Currents of injury: | Different cardiac abnormalities cause part of the heart to remain ________ or _______ ______ all the time

Answer 57

partially or totally depolarized

Question 58

_______ of ______ flows between the pathologically depolarized and the normally polarized areas, even between heart beats.

Answer 58

current of injury

Question 59

Abnormalities causing current of injury: (3)

Answer 59

Mechanical Trauma Infectious Processes Ischemia (most common)

Question 60

Effect of current of injury on QRS complex:

Answer 60

Abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles.

Question 61

J point =

Answer 61

reference point on ECG for analyzing current of injury.