2 - Cardiac Contraction

Question 1

Na+

Answer 1

sodium
extracellular = 135-145 mEq/L
RMP intracellular = 14 mEq/L

Question 2

K+

Answer 2

potassium
extracellular = 3.5 - 5.0 mEq/L
RMP intracellular = higher than extracellular, 140?

Question 3

What does the positive ion concentration gradient result in (RMP)?

Answer 3

positive ion concentration gradient frominsidethe membrane to theoutside causes electronegativity inside the membrane
*nondiffusable, negative ions left inside

Question 4

Most important ions involved in membrane potentials of nerve and muscle cells…

Answer 4

Na+, K+ & Cl-

-determines voltage of membrane potential

Question 5

Cl-

Answer 5

chloride
96-106 mEq/L
during RMP, more extracellularly than intracellularly

Question 6

What prevents all potassium from leaving intracellular compartment during RMP?

Answer 6

electrostatic force

-as more K+ leaves (chemical force), negative forces on inside increase and trap K+ (electrostatic)

Question 7

Nernst Equation

Answer 7

• The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane is called theNernst potentialfor that ion-
• electric potential vs. chemical potential

Question 8

Does any Na+ enter cell during RMP?

Answer 8

yes, small but finite leakage, depolarizing effect

Question 9

Goldman Equation

Answer 9

• calculates membrane potential

- need Na+, K+ and Cl- involved

Question 10

Normal nerve fiber permeability to K+ vs Na+

Answer 10

-the permeability of the membrane to potassium is about 100 times as great as to sodium

Question 11

Action Potential: Activation Gate

Answer 11

• activated at -70, -50 mV
• flips open, allows Na+ to rapidly flow inward
• same conformational change will close gates, just not as quickly

Question 12

Depolarization Stage

Answer 12

• sudden permeability of Na+ ions

- polarity is neutralized as positive ions rush inwards

Question 13

Repolarization Stage

Answer 13

• 10,000th of a second

- Na+ channels begin to close and K+ channels open, reestablishing resting membrane potential

Question 14

Fast Response Action Potentials

Answer 14

Atrial myocardial fibers
Ventricular myocardial fibers
Purkinje fibers

Question 15

Slow-Response Action Potentials

Answer 15

Sinoatrial node
Atrioventricular node
*generated by pacemaker cells - automaticity

Question 16

Autoarhythmic Cell

Answer 16

pacemaker cell, slow-response AP

Question 17

Fast Response Cells

Answer 17

• not automaticity cells

- other cardiac myocytes

Question 18

Channels of Action Potential in Cardiac Muscle Cells

Answer 18

1. ) Voltage activated, fast sodium channels

2. ) L-type calcium channels (slow calcium channels)

Question 19

(RMP) Relative to the outside of a cell is the inside positive or negative in charge?

Answer 19

negative charge

Question 20

(RMP)2. Is potassium higher in concentration inside or outside of a cardiac muscle cell?

Answer 20

inside the cell

Question 21

(RMP) Is sodium higher in concentration inside or outside of a cell?

Answer 21

outside the cell

Question 22

(RMP) What prevents potassium from leaking out of a cell until the concentration is the same on the outside and inside of the cell?

Answer 22

electrostatic force

-chemical force makes k want to leave, but electrostatic prevents

Question 23

(RMP) What ion makes the major contribution to the resting membrane of the cardiac muscle cell?

Answer 23

Potassium

Question 24

(RMP) What ion makes a small contribution to the resting membrane potential?

Answer 24

Sodium

Question 25

(RMP) What ion pump returns ion concentrations back to baseline?

Answer 25

Na+, K+ ATPase pump

Question 26

(RMP) How does the Na+-K+ - ATPase pump contribute to the resting membrane potential?

Answer 26

3 Na+ to outside of cell 2 K+ into cell ATP --> ADP -electrogenic active transport

Question 27

(AP) What ion moves rapidly into a cell during depolarization?

Answer 27

Sodium

Question 28

(AP) What ion exits the cell to restore the baseline electrical charge in a cell during repolarization?

Answer 28

Potassium

Question 29

(AP) What restores ion concentrations back to their baseline levels?

Answer 29

Na+, K+, ATPase pump

Question 30

(EA) In what part of the heart are Fast-Response Action Potentials (non-pacemaker action potentials) found?

Answer 30

Atrial myocardial fibers, ventricular myocardial fibers, purkinje fibers

Question 31

(EA) In what part of the heart are Slow-Response Action Potentials (pacemaker action potentials) typically found?

Answer 31

SA AV Bundle of His

Question 32

(EA) What are some of the differences between Non-pacemaker and Pacemaker action potentials

Answer 32

``` non-pacemakers: 5 phases RMP = -90 mV --> 20 mV depolarize quicker pacemaker: 3 phases RMP = -65 mV --> 10 mV ```

Question 33

(EA) Describe Phase 0 for fast-response/non-pacemaker cells...

Answer 33

Phase 0: depolarization (sodium channels open and change the resting potential of membrane from negative to positive +20 pretty fast

Question 34

(EA) Describe Phase 1 for fast-response/non-pacemaker cells...

Answer 34

Phase 1: Partial Repolarization, sodium channels close, potassium channels open and potassium goes out, making the inner membrane negative

Question 35

(EA) Describe Phase 2 for fast-response/non-pacemaker cells...

Answer 35

Phase 2: Plateau; fast potassium channels close, calcium channels open allowing for some repolarization and the action potential then plateaus due to permeability to sodium and decreased permeability to potassium

Question 36

(EA) Describe Phase 3 for fast-response/non-pacemaker cells...

Answer 36

Phase 3: rapid repolarization: calcium channels close and slow potassium channels open, potassium leaves the cell and membrane potential goes back to negative resting level

Question 37

(EA) Describe Phase 4 for fast-response/non-pacemaker cells...

Answer 37

Phase 4: restoration of ionic gradients, return to resting membrane potential

Question 38

Release of a large amount of calcium from the Sarcoplasmic Reticulum is triggered by entry of which ion?

Answer 38

calcium | -blocks tropomysin, allows myosin head to meat with actin

Question 39

What is the function of the Sarcoplasmic Reticulum within a cardiac muscle cell?

Answer 39

regulated intracellular calcium concentration

Question 40

Which ion is the major determinant of the Resting Membrane Potential in Cardiac cells?

Answer 40

potassium

Question 41

What are the phases of Slow Response (Pacemaker) Cells?

Answer 41

Phase 4 Phase 0 Phase 3

Question 42

Slow Response (Pacemaker) Phase 4

Answer 42

Phase 4: Sodium channels open, slow influx of sodium comes in membrane potential slowly starts to depolarize

Question 43

``` Slow Response (Pacemaker) Phase 0 ```

Answer 43

Phase 0: depolarization calcium channels open, calcium comes in so membrane potential is +10

Question 44

``` Slow Response (Pacemaker) Phase 3 ```

Answer 44

Phase 3 repolarization: calcium channels close, potassium channels open (sodium channels are still open but there is more k leaving than sodium coming in)

Question 45

What are the different refractory periods associated with the cardiac action potentials

Answer 45

(ERP) Effective Relative period (no action potential can happen) (RRP) refractory relative period

Question 46

Automaticity

Answer 46

ability that pacemaker cells have to launch their own action potential stimuli

Question 47

What is diastolic depolarization?

Answer 47

- atrial-nodal action potential is slower to develop than ventricular muscle action potential. - d/t movement of oins

Question 48

What effects on aspects of diastolic depolarization will cause changes in heart rate?

Answer 48

autonomic nervous system

Question 49

Which pacemaker region of the heart is typically dominant

Answer 49

SA node

Question 50

What is Overdrive Suppression

Answer 50

SA node fires quickest, other pacemaker cells do not fire as well

Question 51

What is a sarcomere?

Answer 51

Segment between the two Z lines represents the contractile unit, the sarcomere.

Question 52

Cardiac cells are arranged in a branching network that is known as what

Answer 52

Functional syncytium

Question 53

What are T-tubules in a cardiac muscle cell?

Answer 53

T- tubules are deep invaginations in the sarcolemma membrane Permits ion exchange between extracellular and intracellular compartments to occur deep in the myocyte during depolarization and repolarization.

Question 54

What is the Sarcoplasmic Reticulum?

Answer 54

Extensive branching network that surrounds the myofilaments, activated by influx of calcium from interstitial fluid during action potential and releases more calcium.

Question 55

What is this process called whereby large amounts of calcium are released from the Sarcoplasmic Reticulum into the cell

Answer 55

CICR | Calcium Induced Calcium Release

Question 56

The presence of what ion allows binding between actin and myosin

Answer 56

Calcium

Question 57

What is the function of Troponin in the binding between actin and myosin

Answer 57

At resting state, inhibits binding of actin and myosin