Lecture 24 10/18/23

Question 1

What does it mean for cardiomyocytes to be excitable?

Answer 1

an electrochemical gradient is maintained across their cell membranes

Question 2

What is the stimulation of cardiomyocytes?

Answer 2

momentary reversal of trans-membrane potential (an action potential)

Question 3

What are the characteristics of the action potential?

Answer 3

-initiates excitation-reaction coupling
-stimulus for myocardial shortening

Question 4

What determines membrane potential?

Answer 4

conductance of ions (Na+, K+, Ca2+)

Question 5

What are the two electrophysiologically distinct populations of cells?

Answer 5

-specialized conduction cells
-working cardiomyocytes

Question 6

What are the characteristics of specialized conduction cells?

Answer 6

-depolarize spontaneously
-exhibit automacity

Question 7

What is the role of working cardiomyocytes?

Answer 7

responsible for contraction

Question 8

When do working cardiomyocytes get excited?

Answer 8

when there is an action potential to stimulate them

Question 9

How does the AV node give rise to perkinje fibers?

Answer 9

-AV node gives rise to common bundle/His
-common bundle splits into bundle branches
-bundle branches give rise to perkinje fibers

Question 10

Which structures have cells that exhibit normal automaticity?

Answer 10

-SA node
-AV node
-His/purkinje system

Question 11

What is the role of the fibrous skeleton?

Answer 11

to electrically isolate the atria and ventricles

Question 12

Why is it important for the atria and ventricles to be electrically separated?

Answer 12

allows for the atria and ventricles to depolarize separately

Question 13

What is unique about the AV bundle?

Answer 13

it penetrates the fibrous skeleton

Question 14

What is the role of gap junctions?

Answer 14

rapid diffusion of ions between cells

Question 15

What things contribute to the negative resting membrane potential of the cell?

Answer 15

-Na/K pump
-Donnan effect
-selective permeability of membrane to K, but not Na (K leaks)

Question 16

What type of current is associated with potassium?

Answer 16

outward current

Question 17

What are the two types of channels for potassium and their functions?

Answer 17

-voltage gated: repolarization
-inward rectifier: maintain resting membrane potential

Question 18

What type of current is associated with sodium?

Answer 18

inward current

Question 19

What are sodium channels responsible for?

Answer 19

depolarization

Question 20

What type of current is associated with calcium?

Answer 20

inward current

Question 21

What are the two types of Ca channels?

Answer 21

-L type “slow” channels
-T type channels

Question 22

What happens during the 0 phase?

Answer 22

Na+ in and depolarization

Question 23

What happens during the 2 phase?

Answer 23

Ca2+ in and plateau

Question 24

What happens during the 3 phase?

Answer 24

K+ out and repolarization

Question 25

When do the refractory periods occur?

Answer 25

during repolarization

Question 26

What is an absolute refractory period?

Answer 26

when the cell cannot be re-stimulated

Question 27

What is a relative refractory period?

Answer 27

when the cell can be re-stimulated only by a strong stimulus; causes a less robust AP

Question 28

Which ion is associated with depolarization of atrial/ventricular cells?

Answer 28

sodium

Question 29

Which ion is associated with depolarization of nodal cells?

Answer 29

calcium

Question 30

Which type of cells do not spontaneously depolarize?

Answer 30

atrial/ventricular cells

Question 31

Which type of cells do spontaneously depolarize?

Answer 31

nodal cells

Question 32

Why is the SA node the dominant pacemaker?

Answer 32

most rapid inherent rate of discharge of the conduction system

Question 33

What is overdrive suppression?

Answer 33

when depolarization occurs at a rate that exceeds inherent rate, spontaneous depolarization is inhibited

Question 34

Why is overdrive suppression important?

Answer 34

it prevents competition of automatic tissues

Question 35

What are the mechanisms of spontaneous depolarization?

Answer 35

-deactivation of K+ channels -influx of Na+ -influx of Ca+

Question 36

How does the sympathetic nervous system impact spontaneous depolarization and heart rate?

Answer 36

increases rate

Question 37

How does the parasympathetic nervous system impact spontaneous depolarization and heart rate?

Answer 37

decreases rate

Question 38

What are the characteristics of sympathetic cardiac innervation?

Answer 38

-diffuse distribution -norepinephrine is main transmitter

Question 39

What are the characteristics of parasympathetic cardiac innervation?

Answer 39

-vagal innervation of conduction system -acetylcholine is main transmitter

Question 40

Why is it important that APs in cardiac cells have a greater duration than in nerve cells?

Answer 40

prevents development of physiologic tetanus