Cardiac AP - Slow Response/Timing Cells

Question 1

what maintains phase 4 in slow response cells?

Answer 1

funny current (Na/K)

Question 2

what does funny current do?

Answer 2

provokes spontaneous depolarization

Question 3

what controls heart rate?

Answer 3

rate (slope) of spontaneous depolarization

Question 4

what dominates upstroke in slow response cells?

Answer 4

Ca channels

Question 5

what do muscarinic receptors do to channels?

Answer 5

decrease iF (funny channel) to hyperpolarize, and increases iK (leading to decreased cAMP)

Question 6

what do adrenergic receptors do to channels?

Answer 6

increase iF and iCa to depolarize faster and decreases iK to be less polarized (more frequent AP)

Question 7

is there a phase 1?

Answer 7

no

Question 8

is there a plateau?

Answer 8

no

Question 9

what causes phase 3? repolarization

Answer 9

increased gK through iK and iK1 channels

Question 10

is there iK1 channel during phase 4?

Answer 10

no

Question 11

difference between SA and AV node

Answer 11

SA depolarizes more, faster, triggered first, and reaches threshold faster

Question 12

what if SA node is knocked out?

Answer 12

slower AP from AV node, reduced force

Question 13

what occurs if iF turns on during repolarization?

Answer 13

causes spontaneous depolarization

Question 14

how does gCa increase?

Answer 14

responds to spontaneous depolarization from iF (and initiates AP)

Question 15

action during phase 4

Answer 15

iK and iK1 turn off during phase 4, allowing funny current to depolarize

Question 16

when does funny current turn on?

Answer 16

once cell repolarized and causes spontaneous depolarization

Question 17

what channel repolarizes cells?

Answer 17

iK

Question 18

what is threshold of slow response cell?

Answer 18

-40mV

Question 19

threshold of fast response cell

Answer 19

-65mV

Question 20

what is resting potential of slow response cell

Answer 20

less negative than myocardial cells

Question 21

which cell is more likely to be blocked ?

Answer 21

slow response cells

Question 22

what is conductance speed of slow response?

Answer 22

slower than fast

Question 23

what is post-repolarization refractoriness?

Answer 23

that the relative refractory period extends into phase 4 resting potential, which decreases conduction velocity of impulses that arrive early

Question 24

how do slow respond cells keep rhythm

Answer 24

relative refractory period lasts until phase 4 resting potential and decreases conduction velocity of the impulses that arrive early

Question 25

what occurs if interval between AP is short?

Answer 25

next AP amplitude is short, or may be blocked.

Question 26

benefit of post-repolarization refractoriness

Answer 26

allows ventricles to fill

Question 27

calcium current in SA node

Answer 27

little calcium current, but it is important for membrane potential

Question 28

why is resting potential less than ventricular myocytes?

Answer 28

1. fewer iK1 so there is no efflux of K | 2. ratio of gK and gNa is low so cell deviates more from the E of K

Question 29

What influences AP frequency of SA node?

Answer 29

1. slope of phase 4 spontaneous depolarization 2. maximal negativity during phase 4 (starting more hyperpolarized vs more depolarized) 3. threshold potential

Question 30

how do you change threshold potential?

Answer 30

close some Ca channels to make threshold less negative, therefore need to depolarize more to reach threshold (takes longer)

Question 31

how do you change slope of phase 4?

Answer 31

decrease iF

Question 32

how do you change negativity of phase 4?

Answer 32

hyperpolarize cell so starts from lower starting point)

Question 33

what is overdrive suppression?

Answer 33

when HR is excessively high, Na builds up in the cell, which drives Na/K ATP pump at a higher rate, which makes cell more hyperpolarized. therefore, after period of high HR (once stimulus is turned off) may be period of unusually low rate

Question 34

what do muscarinic receptors do to slow response cells?

Answer 34

M2 increases gK (which hyperpolarizes the cell) by decreasing cAMP

Question 35

how does acetylcholine affect M2?

Answer 35

1. regulates K channels (suppresses them) 2. depresses iF Na current and Ca current (less depolarization) 3. M2 increases gK by decreasing cAMP

Question 36

effect of muscarinic activation on HR?

Answer 36

1. lowers slope of phase 4 2. raises threshold by closing ca channels 3. slows HR!

Question 37

what occurs during hypocalcemia?

Answer 37

depresses AP amplitude and rate of spontaneous depolarization

Question 38

how does norepi affect slow response cells?

Answer 38

1. increases Na permeability during phase 4 (increase iF slope) 2. increases gCa via increasing cAMP (opens Ca channels) (increases amplitude)

Question 39

what do CCB (calcium channel antagonists) do

Answer 39

reduce phase 4 and phase 0 slopes in pacemaker cells, reduces plateau in myocytes

Question 40

what finding by EMG most strongly and specifically supports dx of neurogenic myopathy?

Answer 40

decreased frequency of muscle depolarization with motor nerve stimulation

Question 41

what would a decrease in gCl do in a muscle cell?

Answer 41

spontaneous depolarization, causing spontaneous muscle contractions

Question 42

electrical stimulation has normal amplitude and conduction velocity but AP decreases in amplitude with each stimulus. resting membrane potentials of neurons and myocytes is normal. what's wrong.

Answer 42

myasthenia gravis, something wrong at motor end plate

Question 43

what causes irreversible neural disorders?

Answer 43

deficiency in NO synthase NOS, poly-ADP-ribose polymerase PARP, or superoxide dismutase (SOD)

Question 44

delayed inactivation of voltage gated Na channels in skeletal muscle most likely to cause what?

Answer 44

spontaneous AP and efflux of K causing hyperkalemia

Question 45

what causes neurogenic myopathy?

Answer 45

destruction of alpha motor neurons

Question 46

what would demyelination cause

Answer 46

decreased sensory transmission and motor disorders

Question 47

what does hypercalcemia do?

Answer 47

inacctivates na channels