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Physiology I > Cardiac > Flashcards

Cardiac Flashcards

(57 cards)

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1
Q

What is the threshold of the SA node

A

-40mV

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2
Q

What is the resting potential of a ventricular fiber

A

-80 to -90

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3
Q

What is the resting membrane potential of the SA node

A

-55 to -60mV

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4
Q

The SA node is composed of what

A

Special cardiac muscle fibers

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5
Q

The SA node connects to what

A

Directly to the Atrial fibers

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6
Q

The AV node receives signal form the SA node ____ after origin

A

.03 seconds

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7
Q

How long is the signal delayed in the AV node

A

.09 seconds

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8
Q

Why is signal delayed in the AV node

A

due to small size of cells, low amplitude of AP, and slow rate of depolarization during excitation

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9
Q

How long is the final delay of signal in the penetrating bundles of the AV node

A

.04 seconds

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10
Q

How long is the overall delay from the initial origin of the signal until onset of ventricular contraction

A

.16 seconds

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11
Q

The slow conduction in the conductive system of the heart is caused mainly by ______ resulting in an increase in the ________

A

Diminished number of gap junctions along the pathway, resulting in an increase in the resistance to conduction

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12
Q

What is the resting membrane potential of the SA node fiber

A

-55 to -60 mV (Threshold= -40mV)

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13
Q

Why are fast sodium channels in the SA node already inactivated at resting potential

A

Inactivation gates close when membrane potential is less negative than -55mV
- The SA node fiber has a resting membrane potential of -55–60mV

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14
Q

Why is atrial nodal AP slower to develop than ventricular

A

Only slow sodium-calcium channels can open and the fast sodium channels are inactivated due to the resting potential of -55- (-60)

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15
Q

When do the sodium-calcium channels become activated

A

at -40mV

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16
Q

how long are the sodium-calcium channels in the SA node open

A

they become inactivated within 100-150msec after opening

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17
Q

When do the potassium channels in the SA node become open

A

at the same time as when the sodium-calcium channels become inactivated

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18
Q

How long do potassium channels remain open in the SA node

A

for a few tenths of a second

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19
Q

What is the ventricular fiber resting potential

A

-85 to -90

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20
Q

The atrial nodes do note have what two phases

A

phase 1 & phase 2

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21
Q

The AP originating in the SA node generate what

A

The “sinus rhythm”

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22
Q

What are action potentials that originate anywhere else than the SA node

A

Ectopic focus or pacemaker

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23
Q

Where is the Vagus nerve main distribution in the heart

Study These Flashcards
A

The SA and AV nodes

24
Q

What is the neurotransmitter used by the Vagus nerve

Study These Flashcards
A

Acetylcholine

25
What is a muscarinic receptor
A receptor that is located on the SA and AV node that is stimulated by the Vagus nerve
26
What effect does the Vagus nerve have on the SA node
it decreases rate of rhythm (negative chronotropic effect)
27
What effect does the Vagus nerve have on the AV junctional fibers
slowing transmission of the cardiac impulse into the ventricles
28
What effect does the vagus nerve have to cardiac fiber membrane permeability
it increases permeability of the fiber membranes to potassium ions - hyperpolarization: -65 to -75 rather than -55 to -60 mV
29
Where is the sympathetic innervation of the heart distributed
to all parts of the heart, mainly the ventricles
30
What is the neurotransmitter used by the sympathetic nervous system
Norepinephrine
31
What effect does norepinephrine have on the heart
stimulates beta-1 adrenergic receptors - increases depolarization rate (positive chronotropic effect) - may increase permeability of fiber membranes to sodium and calcium ions
32
What does the P wave on an EKG represent
Atrial depolarization
33
What does the QRS on an EKG represent
ventricular depolarization
34
What does the T wave on an EKG represent
Ventricular repolarization
35
What do ECG measure
The extracellular potential: it is not the same as the potential recorded form an axon when recording the transmembrane potential
36
What is an ECG
A graphic representation of the electrical activity in cardiac muscle tissue produced by regions of depolarization and repolarization
37
When does deflection from 0 on an ECG occur
only when there is current flow between regions of the heart (when there is variation in the membrane potential in different regions of the heart.) Current flows between regions of different membrane potentials.
38
When does current on an ECG not occur
when only the atria and ventricles have different potentials
39
Ventricular muscle has a _______ action potential
Monophasic
40
The QRS marks the beginning of what
ventricular AP
41
The T wave marks what
The end of the ventricular AP
42
No AP is recorded when the ventricle is ______
completely polarized or completely depolarized
43
Only when the muscle is partly polarized or partly depolarized does ________
Current flow from one part of the ventricle to another
44
Repolarization of the ventricles occurs
after the end of the T wave
45
what is the P-Q (P-R) interval
beginning of P wave----> beginning of QRS - is about 0.16 seconds note that the 0.16 seconds is the same amount of time that an AP gets from the SA node to the ventricular fibers due to the delay system in the AV node.
46
how long is the Q-T interval
0.35 seconds
47
What is the Q-T interval
it is the time from ventricular depolarization to ventricular repolarization
48
The P wave represents what phase of the cardiac cycle in the atria
Phase 0 (rapid depolarization)
49
The T-wave represents what phase of the cardiac cycle in ventricles
phase 3 (repolarization)
50
The QRS represents what phase of the cardiac cycle in ventricles
Phase 0 (rapid depolarization)
51
The T wave represents what phase of the cardiac cycle in ventricles
Phase 3 (repolarization)
52
In a typical ECG, which of the following waves occurs at the beginning of the contraction of the atria
P wave
53
what is typically not seen on an ECG
Atrial repolarization
54
Which of the following is the direction of bipolar lead III
120 degrees
55
Of the three bipolar leads, which one is connected to both left and right arms
Lead I
56
What is the mean electrical axis of the normal ventricles
it is 59 degrees
57
what is the amplitude of the SA node
about 60mv | resting potential is -55 to -60 and the peak is about

Physiology I (8 decks)

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