03a: Electrophysiology

Question 1

Mechanical contraction of cardiac muscle is initiated by a(n) (X), a rapid (re/de/hyper)-polarization of the membrane.

Answer 1

X = action potential

Depolarization

Question 2

Coordinated contraction of heart depends on initiation and spread of (X) over muscle in controlled, sequential manner.

Answer 2

X = action potential

Question 3

T/F: Excitation of heart is neurogenic.

Answer 3

False - myogenic

Question 4

List the three chief physiological properties of cardiac muscle function.

Answer 4

1. Autorhythmicity/excitation
2. Conduction
3. Contraction

Question 5

Pacemaker cells have (well/poorly)-developed contractile capability. Impulses originating there are conducted (quickly/slowly).

Answer 5

Poorly; slowly

Question 6

Certain parts of the heart, such as (X) are specialized for rapid conduction of the impulse. They have (well/poorly)-developed contractile capability.

Answer 6

X = purkinje fibers;

Poorly

Question 7

Which cardiac tissue has the highest degree of contractile power?

Answer 7

Atrial and ventricular muscle

Question 8

List the heart regions in order of normal excitation.

Answer 8

1. SA node
2. AV node
3. Common bundle of His
4. Bundle branches
5. Purkinje fibers
6. Ventricular muscle

Question 9

Non-pacemaker cells feature (small/large) negative value for resting membrane potential: (X) mV. This is due to high/low resting permeability to:

Answer 9

Large;
X = -90

High K+ and low Na+ permeabilities

Question 10

T/F: Non-pacemaker cells of heart have qualitatively same action potential.

Answer 10

True

Question 11

T/F: Non-pacemaker cells of heart have action potentials that are identical in total duration.

Answer 11

False

Question 12

Course of electrical activity of heart is divided into how many phases?

Answer 12

5; phases 0-4

Question 13

Phase 0 of heart AP.

Answer 13

Rapid depolarization (to peak)

Question 14

Phase 1 of heart AP.

Answer 14

Initial repolarization (to plateau)

Question 15

Phase 2 of heart AP.

Answer 15

Plateau

Question 16

Phase 3 of heart AP.

Answer 16

Rapid repolarization (after plateau)

Question 17

Phase 4 of heart AP.

Answer 17

Diastolic interval between successive AP

Question 18

AP of heart lasts (shorter/longer) than nerve fiber AP. And (shorter/longer) than skeletal muscle AP.

Answer 18

Longer than both

Question 19

Why is the duration of cardiac muscle AP almost as long as the contraction?

Answer 19

Acts more than trigger;

1. Controls duration and magnitude of contraction
2. Prevents cells fro becoming excitable before AP is over

Question 20

(Short/long) refractory period in cardiac muscle serves to (allow/prevent) (X).

Answer 20

Long;
prevent;
X = muscle from being re-excited until previous contraction is essentially over

Question 21

T/F: In some cases, Purkinje cells can display spontaneous rhythmic activity.

Answer 21

True

Question 22

Chief distinguishing feature of pacemaker cell electrical activity is:

Answer 22

“Pacemaker potential”; slow depolarization in diastole (that leads to AP)

Question 23

T/F: Membrane of cardiac pacemaker cells is only at rest in diastole.

Answer 23

False - never at rest (slow depolarization in diastole)

Question 24

The “pacemaker potential” is:

Answer 24

slow depolarization occurring in pacemaker cells between discharges (during diastole)

Question 25

Pacemaker cells feature (small/large) negative value for resting membrane potential and AP whose overall time course is (faster/slower) than that of atrial muscle.

Answer 25

Small (closer to zero); | Slower

Question 26

What accounts for the (greater/lesser) negative resting potential in pacemaker cells?

Answer 26

Lesser (closer to zero); | Relatively high resting permeability to Na

Question 27

T/F: Rate of depolarization during pacemaker potential is identical in all pacemaker cells.

Answer 27

False

Question 28

Pacemaker cells having the (highest/lowest) (X) will control the rate of firing of other cell.s

Answer 28

``` Highest; Intrinsic frequency (reach threshold more rapidly) ```

Question 29

True pacemaker of the heart is (X). Reserve pacemaker is (Y).

Answer 29

``` X = SA node Y = AV node ```

Question 30

It can be seen that sympathetic effect of (increase/decrease) HR is due to (increase/decrease) in (X).

Answer 30

Increase; Increase; X = rate of rise in pacemaker depolarization

Question 31

Sympathetic innervation of heart (increases/decreases) maximum diastolic potential and (increases/decreases) rate of rise of (X).

Answer 31

No change; Increases; X = pacemaker potential

Question 32

Vagal innervation of heart (increases/decreases) maximum diastolic potential and (increases/decreases) rate of rise of (X).

Answer 32

Increases; Decreases; X = pacemaker potential

Question 33

Major (specific) effect of Ach, released by (X), is to (increase/decrease) (Y). This leads to (de/re/hyper)-polarization.

Answer 33

X = vagus Increase; Y = membrane permeability to K; Hyperpolarization

Question 34

Which phase of cardiac cycle is the plateau phase, primarily due to (X) ion (influx/efflux)?

Answer 34

Phase 2; X = Ca Influx (counteracts K efflux)

Question 35

Plateau of cardiac cycle is typically around (X) mV.

Answer 35

X = 0

Question 36

Cardiac cycle: Compared to Na channels, Ca channels require (smaller/larger) (de/re/hyper)-polarization to trigger their opening. And they open (quicker/slower). And they are inactivated (quicker/slower).

Answer 36

Larger depolarization; Slower; slower

Question 37

During pacemaker potential, which ion(s) are responsible for (inward/outward) current that will result in depolarization of the membrane?

Answer 37

Inward; | First Na, then later Ca

Question 38

During diastole, conductance of (X) is turned off slowly, to allow slow (re/de/hyper)-polarization of the membrane.

Answer 38

X = K | Depolarization

Question 39

The "funny current" occurs during (X) period of cardiac cycle and is (inward/outward) current carried by (Y). What's so funny about it?

Answer 39

X = diastolic Inward; Y = Na It's carried through Na channel that opens by repolarization (negative voltages)

Question 40

How (specifically) does NE cause (increase/decrease) rate of (X) depolarization?

Answer 40

Increase; X = pacemaker 1. Increase rate of turning off gK (during diastole) 2. Increase gf (funny) and gCa

Question 41

On its way to (X), the electrical activity of heart pauses briefly to permit (Y).

Answer 41

``` X = bundle of His (and ventricles); Y = completion of atrial contraction ```

Question 42

T/F: Normally, conduction of AV node is bidirectional.

Answer 42

False - unidirectional (atrium to ventricles)

Question 43

The AV node will only transmit impulses up to a certain (X), after which various degrees of (Y) will occur.

Answer 43

``` X = frequencies; Y = heart block ```

Question 44

Sympathetic and vagal stimulation affect (X) speed through (Y) node.

Answer 44

``` X = conduction Y = AV ```

Question 45

Cardiac excitation: Once conduction reaches (X), the speed picks up and impulse spreads rapidly into (Y) network.

Answer 45

``` X = bundle of His Y = purkinje ```

Question 46

Role of Ca in initiating contraction: (influx/efflux) of (intra/extra)-cellular Ca triggers release of (X) from (Y).

Answer 46

Influx; Extracellular; X = Ca Y = SR

Question 47

T/F: During plateau, uptake of Ca by SR is occurring.

Answer 47

True

Question 48

Sympathetic stimulation causes AP with (higher/lower) plateau amplitude due to (greater/smaller) (X).

Answer 48

Higher; Greater; X = gCa

Question 49

Sympathetic stimulation causes AP with (longer/shorter) duration in part from (faster/slower) (X).

Answer 49

``` Shorter Faster X = 1. Inactivation of inward Ca current 2. Activation of repolarizing K current ```