Electrophysiology of the Heart

Question 1

Na+ gradients

Answer 1

concentration - more outside the cell

electrical - more outside the cell

Question 2

K+ gradients

Answer 2

concentration - more inside the cell

electrical - more outside the cell

Question 3

Ca++ gradients

Answer 3

concentration - more outside the cell

electrical - more outside the cell

Question 4

Cl- gradients

Answer 4

concentration - more outside the cell

electrical - more inside the cell

Question 5

Protein- gradients

Answer 5

concentration - more inside the cell

electrical - more inside teh cell

Question 6

Na+ permeability at rest

Answer 6

not permeable

Na/K ATPase is pumping it out of the cell

Question 7

K+ permeability at rest

Answer 7

permable

Question 8

Ca++ permeability at rest

Answer 8

not very permeable

concentration maintained by active sequestration into SR

Question 9

Phase 0 permabilities

Answer 9

increased permeability to sodium

Question 10

Phase 1 permabilities

Answer 10

decreased permeability to sodium

Question 11

Phase 2 permeabilities

Answer 11

increased permeability to calcium

decreased permeability to K+

Question 12

Phase 3 permeabilities

Answer 12

increased permeability to K+

decreased permeability to Ca++

Question 13

When does Fast Na+/Ca++ channel open

Answer 13

Phase 0

Question 14

When does slow Na+/Ca++ channel open

Answer 14

Phase 2

Question 15

Effective refractory period

Answer 15

absolute refractory period, begins at upstroke of phase 0 and ends when Na+ channels are reset to resting potion in phase 3

Question 16

Why can the heart not undergo tetany

Answer 16

because of the effective refractory period

Question 17

Relative refractory period

Answer 17

begins where ERP ends. Ends when normal AP can be generated

Question 18

Phase 0 of SA nodal pacemaker AP

Answer 18

upstroke/depolarization

Ca++ enters cell

Question 19

Phase 3 of SA nodal pacemaker AP

Answer 19

repolarization

K+ exits cell

Question 20

Phase 4 of SA nodal pacemaker of AP

Answer 20

slow depolarization/pre potential

Na+ enters cell via funny current

Question 21

Example of positive Chronotroph

Answer 21

norepinephrine, epinephrine, isoproterenol

Question 22

What does positive chronotroph do

Answer 22

increases permeability of nodal cells to N+ and Ca++

increases HR

Question 23

What does postiive chronotroph do to slope

Answer 23

increased slope of phase 4

Question 24

Example of negative chronotroph

Answer 24

acetylcholine

Question 25

What does negative chronotroph do

Answer 25

increased permeability of nodal cells to K+, lowers resting potential
decreases HR

Question 26

What does negative chronotroph do to slope

Answer 26

lowers slope of phase 4

Question 27

What are ectopic foci

Answer 27

superexcitiable cells

Question 28

What is the function of ectopic foci as fail safe mechanism

Answer 28

it helps if you have a blockage, the highest rate will pace the heart

Question 29

Sequence of depolarization of the heart

Answer 29

SA node –> atrial muscle cells —> AV node —> septum –> apex —> free walls –> LV base

Question 30

function of SA node

Answer 30

normal pacemaker for heart

Question 31

function of AV node

Answer 31

delays impulse, secondary pacemaker

Question 32

function of His bundle

Answer 32

normally only communication point between atria and ventricles

Question 33

Function of purkinje fivers

Answer 33

very rapid transmission of signal, synchronous contraction of ventricles, tertiary pacemaker, only penetrate to subendocardium

Question 34

average vector for atrial depolarization and duration

Answer 34

gap junctions/direct contact with neighboring atrial muscle cells. spread is instantaneous

Question 35

average vector for ventricular depolarization and duration

Answer 35

purkinje fibers, quick at first but then spreads via mycoyte connections which are slower

Question 36

how does hyperkalemia increase chance of fatal dysrthymia

Answer 36

hyperkalemia slows HR, blocks AV conduction and dilation of heart, cell membrane is partially depolarized which reduces intensity of AP and makes heart progressively weaker