Lecture 3 - Slow type AP and cardiac activation

Question 1

the myocardial AP being classified as slow or fast refers to the rate of the

Answer 1

initial membrane polarization

Question 2

__ cells generate membrane depolarization spontaneously

Answer 2

pacemaker

Question 3

__ channels are activated by hyperpolarization and are closed during depolarization (opposite of fast type channel)

Answer 3

funny Na channels

Question 4

only a small group of mycardial cells have __ properties and these trigger synchronous contraction of the whole heart

Answer 4

pacemaker-like

Question 5

Phase 4 slow type

Answer 5

RMP - a slow spontaneous depolarization during rest/diastole

Question 6

__ is a slow influx of Na ions through funny Na channels that cause spontaneous depolarization

Answer 6

pacemaker current

Question 7

why don’t the fast Na channels activate in pacemaker cells

Answer 7

RMP is less negative so they remain inactivated

Question 8

phase 0 or __ is entirely dependent on __ influx

Answer 8

slow AP depolarization, Ca

Question 9

which phases are absent in pacemaker cells

Answer 9

phases 1 and 2 (no initial repolarization or plateau)

Question 10

phase 3 or __ has increase in __ outflow/conductance whic repolarizes the membrane potential

Answer 10

slow repolarization, K+

Question 11

__ node cells generate AP with a faster rate of depolarization (phase 0) than other __ cells

Answer 11

SA node, pacemaker (AV, Purkinje)

Question 12

__ is the speed at which AP propagate from one area to another

Answer 12

conduction velocity

Question 13

conduction velocity varies greatly in different areas, AV node is made of __ that conduct much more slowly compared to the __ purkinje fibers that are fast conducting

Answer 13

small fibers, large fibers

Question 14

__ cells have shorter duration AP than __ cells

Answer 14

atrial, ventricular

Question 15

atrial cells are not electrically coupled with the ventricle cells except through the __ tissue

Answer 15

AV node

Question 16

If the SA node dysfunctions the AV node can take over but it will generate a __ HR. The AV node is also known as the __

Answer 16

slower, latent pacemaker

Question 17

The conduction delay between the AV and bundle of His allows for

Answer 17

atria to finish contraction prior to depolarization of ventricles

Question 18

conduction through the ventricles (bundle of His and purkinji) is fast or slow

Answer 18

fast

Question 19

__ are important in the AV node so that retrograde excitation from the ventricular muscles can’t pass back to the atrium.

Answer 19

refractory properties (longer in pacemaker cells)

Question 20

if the SA and AV nodes fail __ drives the heart at a very slow HR (30-40 bpm), this may be insufficient to maintain CO and BP in p with heart disease and can = syncopy or death

Answer 20

his-purkinje system

Question 21

AV node cells have __ discharge rate compared to SA node

Answer 21

slower

Question 22

Slow conduction through the AV node/delay allows for

Answer 22

ventricular filling (diastole)

Question 23

AV node cells have longer refractory periods to protect ventricles from __ and prevent __

Answer 23

premature contraction, retrograde excitation

Question 24

__ is the beginning of the specialized conduction system in the ventricles. it separates into left and right bundle branches, the __ bundle is bigger and depolarizes first

Answer 24

bundle of His, left

Question 25

__ are the largest diameter fibers in the heart and have the fastest conduction velocity and longer __ phase

Answer 25

purkinje fibers, plateau (phase 2) - protects ventricles from premature atrial contractions

Question 26

purkinje fibers are known as __ pacemakers

Answer 26

tertiary

Question 27

papillary muscles and septum depolarize/contract first. Papillary m. contraction prevents __ of the AV valves into the atria during ventricular contraction

Answer 27

eversion

Question 28

myocardial depolarization is followed by muscle __ and then __

Answer 28

contraction, relaxation.

Question 29

during relaxation cells are

Answer 29

refractory

Question 30

RMP (phase 4) has a maximum negative potenial that is reached, this is referred to as the __. It is variable and depends on K and Na conductance via ANS input to pacemaker cells

Answer 30

maximum diastolic potential (MDP)

Question 31

Phase 4 = fluctuating

Answer 31

Na (funny) and K

Question 32

phase 0 =

Answer 32

Ca conductance

Question 33

Phase 3 =

Answer 33

K outflow/conductance (delayed rectifier VG channel)

Question 34

normal sequence of depolarization

Answer 34

1. SA 2. atrial tissue 3. AV 4. septum/His 5. papillary-purkinje 6. apex 7. base (left then right ventricle)