Electrophysiology

Question 1

What are characteristics of cardiac myocytes not present in other muscle cells?

Answer 1

1. branching muscle fibers
2. cardiac myocytes are connected with intercalated discs

Question 2

What are the function of intercalated disks? What do they contain?

Answer 2

Allow action potentials to propagate from cell to cell
Gap junctions

Question 3

What is functional syncitium?

Answer 3

an AP can be induced & depolarization will travel from cell to cell via INTERCALATED DISCS and BRANCHING

aka: entire myocyte mass is depolarized by following the cell before it– cells working together

Question 4

What prevents tetanization (spasm) of cardiac muscle

Answer 4

cyclic movement of Ca+2
- cells have a moment of rest

Question 5

What ion channels alter cardiac muscle cell charge?

Answer 5

1) voltage-gated ion channels = Na+, Ca+2, K+
2) ligand-gated ion channels = many K+
3) stretch-activated ion channels

Question 6

What do stretch-activated ion channels do?

Answer 6

changes the amount of Ca+2 allowed to enter myocyte with each beat

Question 7

What is the equation for calculating total current?

Answer 7

Total current (I) = N x i x p

Question 8

What maintains the negative resting membrane potential of cardiac cells?

Answer 8

Sodium Potassium ATPase pump
2K+ in/ 3 Na+ out

Question 9

Which Ca+ pumps are steady state or opened at depolarization?

Answer 9

1) Na+/Ca+ pump = steady state
Voltage-gated
2) Ca+2 channels (VOCC) = open at depolarization

Question 10

T or F: nerve and skeletal muscles have the slowest AP duration

Answer 10

F: cardiac myocyte AP duration is the slowest
- due to prolonged period of Ca+2 entry

Question 11

Four phases of ventricular cardiac myocyte AP

Answer 11

Phase 0: Na+ floods cell - resting potential becomes more (+)
Phase 1: Na channels INACTIVE, some K+ channels leaking outward
Phase 2: VOCC activated - Ca+2 begins entering cell
Phase 3: Ca+2 entering cell decreases, K+ charge being retified
Phase 4: resting membrane

Question 12

What are the two types of action potentials in myocardial cells?
which type in which cell (pacemaker and contractile myocyte)

Answer 12

Fast response = contractile cells
Atrial myocytes
Ventricular myocytes
Slow response = pacemaker
Sino-Atrial node
Atrio-Ventricular node
Bundle of His and Purkinje fibers

Question 13

What are the two types of contractile FAST response cells?

Answer 13

Atrial myocytes
Ventricular myocytes

Question 14

Why are ATRIAL myocytes faster than ventricular myocytes?

Answer 14

• less Ca+2 is needed to contract because it is a lower pressure system than the ventricular myocytes
  this means short phase 2

Question 15

What are the three slow response myocardial cells?

Answer 15

Sino-Atrial node
Atrio-Ventricular node
Bundle of His and Purkinje fibers

Question 16

What drives phase 4 of slow response action potentials?

Answer 16

interaction of K+/Na+ channels opening and closing

Question 17

What is the dominate pacemaker of the heart? Where is it located?

Answer 17

Sino-Atrial node
Right atrium

Question 18

What is the electrical connection between THE ATRIUM

Answer 18

Bachmann’s bundle - connects SA node to the left atrium

Question 19

What is the AV node? Where is it located?

Answer 19

atrioventricular node - bottom of the right atrium

Question 20

How does the SA node communicate with the AV node?

Answer 20

3 internodal tracts in the right atrium

Question 21

How does the atrial electric communicate or connect to ventricular electric?

Question 22

Describe the branching pattern of the AV node after the bundle of His?

Answer 22

• left and right bundle branch (LBB & RBB)
• left bundle branch branches into anterior & posterior fascicle
• at the end of anterior and posterior fascicles and RBB, there are Purkinje fibers

Question 23

What are the species differences between locations of Purkinje fibers?

Answer 23

dogs = in endocardium
cows and most other species = diffuse through myocardium

Question 24

Describe a cardiac pacemaker cell action potential

Answer 24

• depolarization occurs due to Na+ entering and K+ leaving decreases
• Ca+2 begins entering cells and threshold is reached causing AP

Question 25

What entering the cardiac cells causes the contraction

Answer 25

Ca+

Question 26

Why are pacemaker cells slower than atrial/ventricular myocytes?

Answer 26

absence of fast Na+ channels during the depolarization period (cells become more positive slower than atrial/ventricular myocytes)

Question 27

How do acetylcholine and norepineprine change heart rate?

Answer 27

Acetylcholine decreases the rate of depolarization and lengthens the interval between action potentials decreases heart rate
Norepinephrine increases the rate of depolarization and shortens the interval between action potentials increases heart rate

Question 28

Describe the overall action potential/contraction process of the heart

Answer 28

1) SA node reaches threshold –> AP across right atria to left atria
2) Bachmann’s bundle carries electrical current to left atria (both atrium contract - left slightly slower),
3 internodal tracts communicate with AV node
3) AP travels down AV node through bundle branches to apex of heart, atria done contracting
4) both ventricles contract from Purkinje fibers

Question 29

What are the two refractory periods present in myocardial cells? Which one is absolute (no AP can be excited)?

Answer 29

1) Effective refractory period (ERP) - absolute - no AP can be excited

2) Relative refractory period (RRP) - strong enough stimuli could produce AP

Question 30

What happens when AP occur to closely together?

Answer 30

arrhythmias