CV 3

Question 1

3 causes of dysrhythmias

Answer 1

Alterations in resting potential
Channel malfunction
Conduction defects

Question 2

What are the concentrations for:
Na
K
Ca
inside the cell?

Answer 2

Na 10 mM
K 135 mM
Ca 0.0001 mM

Question 3

What are the equilibrium potentials for:
Na
K
Ca

Answer 3

Na +70 mV
K -94mV
Ca +132 mV

Question 4

What is the normal resting potential?

Answer 4

-85 mV

Question 5

What 2 factors contribute to the membrane potential?

Answer 5

Concentration gradient and membrane conductance of each ion

Question 6

Phases of a fast AP

Answer 6

Upstroke (Na+ inward current)
Initial repolarization (K+ outward current)
Plateau 
Repolarization
Stable resting potential

Question 7

Absolute refractory period

Answer 7

No way to get another AP

From the rapid depol until about threshold level of stage 3

Question 8

Relative refractory period

Answer 8

Greater than normal stimulus needed to get AP

From midway through part 3 to part 4

Question 9

Funny current

Answer 9

Carried by HCN channels
Activated by hyperpolarization
Carried by both Na and K ions
Active during diastolic depolarization

Question 10

L-type Ca current

Answer 10

Responsible for late phase of diastolic depolarization

Also primarily responsible for the slow AP upstroke

Question 11

Delayed rectifier K current

Answer 11

Responsibel for slow AP repolarization
Ensures SA node myocytes return to a membrane potential at which the funny current and L-type Ca channels can be activated to initiate the next slow AP

Question 12

How does sympathetic activation by norepinephrine work?

Answer 12

NOR acts at the beta-1 adrenergic receptors (as an agonist) to increase the spontaneous AP frequency by increasing the If and Ica-L which increases the slope of the diastolic depolarization
Moves at a faster rate up to threshold

Question 13

How does parasympathetic activation by acetylcholine work?

Answer 13

M2 receptor agonist

1. Decreases spontaneous AP frequency by decreasing If and Ica-L, which decreases the slope of diastolic depolarization
2. Activates the ACh-sensitive K current, which hyperpolarizes the max diastolic potential and decreases spontaneous AP frequency

Question 14

Intrinsic firing rate of the normal pacemaker

Answer 14

About 100 beats per min

But with innervation it is kept around 70

Question 15

Latent pacemakers

Answer 15

Other cells of the conduction system normally suppressed

Can act as pacemaker if the normal pacemaker gets too low

Question 16

5 things you can interpret from the ECG

Answer 16

Heart rhythm
Heart rate
Intervals
Abnormalities of P wave, QRS, ST segment, and T wave
Mean QRS axis

Question 17

Tachycardia and bradycardia HRs

Answer 17

T: greater than 100 bpm
B: less than 60 bpm

Question 18

First degree AV block

Answer 18

The impulse through the AV node is slightly longer

PR interval is lengthened

Question 19

Second degree AV block

Answer 19

When one or more (but not all) of the atrial impulses fail to conduct to the ventricles due to impaired conduction

Question 20

Third degree AV block

Answer 20

When the impulse generated in the SA node does not propagate to the ventricles
Accessory pacemakers then take over
Calculate HR from P waves and then from R-R, will see large differences