lecture 19- cardiovascular foundations II

Question 1

myocaridal cells (myocytes)

Answer 1

99% of the cells
contractile force
the force producing cells: striated muscle fibers

Question 2

autorhythmic (pacemaker) cells

Answer 2

generate spontaneous, rhythmic APs

–> do not contribute to the contractile force of a muscle

Question 3

both myocytes and pacemaker cells can generate…

Answer 3

APs

Question 4

ventricular myocyte APs
(myocardial contractile cells)

Answer 4

• resting membrane potential is -90mV
• AP is initated when wave of depolarization enters cells
• AP divided into 4 phases
• long AP duration (about 200msec)

Question 5

What are the 3 channels in generating ventricular action potential

Answer 5

1. voltage gated Na+ channels
2. voltage gated Ca2+ channels
3. a number of different voltage-gated K+ channels

Question 6

ventricular AP: what are the diff types of voltage gated K channels?

Answer 6

slow
medium
fast
leak

Question 7

ventricular AP shape (curve on graph) is due to

Answer 7

time-dependent opening and closing of different voltage-gated ion channels
- speed of opening is different for every channel

Question 8

Ventricular AP: Na+ channels

Answer 8

similar function to those in neurons:
-fast activating
-fast inactivating
-membrane must repolarize for them to reset (refractory period)

Question 9

Ventricular AP: Ca2+ and K+ channels

Answer 9

also open w membrane depolarization but take longer to open
(Ca2+ is faster than K+ though)

Question 10

5 phases of ventricular AP

Answer 10

*starts at 4
0= rapid upstroke/depolarization
1= notch
2= plateau (tug of war)
3= rapid repolarization
4= at rest

Question 11

ventricular AP phase 0

Answer 11

Na+ channels open
Na+ in (upstroke/depolarization, was -90mV at resting)

Question 12

ventricular AP phase 1: notch

Answer 12

Na+ channels inactivate. Fast K+ channels open (repolarization).

Na+ flow stops. K+ flows out (brief)

Question 13

ventricular AP phase 2: plateau

Answer 13

fast K+ channels close and slower K+ channels open.
Ca2+ channels open.

K+ flows out. Ca2+ flows in

initially Pk=Pca (equilibrium)

Question 14

ventricular AP phase 3: repolarize

Answer 14

Ca2+ channels inactivate. Slow K+ channels open.

Ca2+ flow stops. K+ flows in

Question 15

ventricular AP phase 4: at rest

Answer 15

slow K+ channels close.
(Kv close but K leak stay open)

K+ out through leak channels.
Na+-K+ATPase

Question 16

tetanus

Answer 16

the fusion of contractions to produce a continuous contraction

Question 17

the long cardiac AP prevents…

Answer 17

summation and tetanus

Question 18

compare refractory period in cardiac muscle vs skeletal muscle AP

Answer 18

cardiac muscle fiber: refractory period is almost as long as the entire muscle twitch

skeletal muscle fast twitch fiber: refractory period is very short compared to amount of time needed for the development of tension

Question 19

compare summation and tetanus in cardiac vs skeletal muscle AP

Answer 19

cardiac: long refractory period prevents tetanus

skeletal muscles are stimulated repeatedly, they will exhibit summation and tetanus
(tension sums w/ each twitch)

Question 20

pacemaker APs are driven by

Answer 20

“funny” channels

Question 21

pacemaker APs

Answer 21

• no stable resting membrane potential
• pacemaker potential between APs
• due to If current through “funny”/HCN channel:
  –> HCN channels conduct both Na+ and K+ in.
  Net Na+ IN leads to depolarization.

Question 22

HCN channel=

Answer 22

hyperpolarization-activated cyclic nucleotide gated channels

(pacemaker channels, funny channels)

Question 23

APs rhythmically initiated in —- cells set the pace of the heart

Answer 23

SA node

Question 24

SA nodes lie at the junction between

Answer 24

superior vena cava and right atrium

Question 25

where are autorhythmic cells localized to?

Answer 25

specialized tissues of conduction
(wiring and insulation for atria and ventricles to contract)

Question 26

Ventricular conduction system

Answer 26

AV node –> the common AV bundle (bundle of His) –> divides into left and right bundles –> bundles give rise to Purkinje fibers

Question 27

AV (atrio ventricular) nodes lie in the

Answer 27

inter-atrial septum

–> the only pathways for electrical conduction across connective tissue between atria and ventricles

Question 28

SA node function

Answer 28

sets the pace of the heartbeat at 70 bpm

Question 29

AV node function

Answer 29

routes direction of electrical signals

delays transmission of APs
(PAUSE! atria need to finish contracting before ventricles contract)

AV node can act as pacemaker under some pathological conditions (fires at 50 bpm) too slow!

Question 30

what other fibers also have pacemaker properties?

Answer 30

Purkinje fibers (35 bpm)

Question 31

what cells is HR set by?

Answer 31

the fastest pacemaker cells in the circuit
(SA node)

Question 32

APs are continually and spontaneously initiated in the

Answer 32

SA node

Question 33

APs spread through — system of the heart

Answer 33

electrical conducting

Question 34

when APs pass across atria and ventricles….

Answer 34

depolarization spreads acorss myocytes

APs depolarize the myocyte membrane

myocyte contracts

Question 35

Einthoven’s triangle and ECG

Answer 35

represents global electrical activity of the heart

• mostly measures spread of depolarization through heart muscle

Question 36

ECG: P wave=

Answer 36

atrial depolarization

Question 37

ECG: QRS complex=

Answer 37

atrial repolarization and ventricular depolarization

Question 38

ECG: T wave=

Answer 38

ventricular repolarization

Question 39

Tachycardia

Answer 39

HR is FASTER than normal

Question 40

Bradychardia

Answer 40

HR is SLOWER than normal

Question 41

Fibrilation=

Answer 41

electrogram is disorganized

Question 42

Atrial fibrilation=

Answer 42

heart still functions as a pump

• atria keeps fluttering, doesn’t fully relax
• not life threatening

Question 43

Ventricular fibrilation=

Answer 43

heart does not function as an effective pump

• life threatening
• ventricles fluttering