Cardiovascular, Cardiac Cell Physiology

Front 1

describe the T-tubules of ventricular and atrial muscle cells?

Back 1

Ventricular = Very large (much larger than skeletal muscle T-tubules) and filled with glycocalyx

Atrial = virtually non-existent

Front 2

what sepperates muscle fibers end-to-end?

Back 2

intercalated disks

Front 3

while cardiac muscle cells are not a true syncytium what allows them to function as such?

Back 3

gap junctions between all the cells allow electrical signals to rapidly pass from cell to cell

Front 4

aside from cardiac muscle cells, what other type of cells can be found in the heart?

Back 4

non-contractile cells also which serve as conduction cells

characterized by absence of myofibrils

Front 5

depolarization in fast action potentials is created by what ion flux and in what direction?

Back 5

Na+ influx

Front 6

depolarization in slow action potentials is created by what ion flux and in what direction?

Back 6

Ca+ influx

Front 7

what is responsible for the slight return to negative membrane potentials during phase 1 of fast action potentials?

Back 7

K+ efflux

Front 8

during phase 2, what causes the action potential repolarization to slow?

Back 8

the efflux of K+ is somewhat offset by the influx of Ca++

Front 9

what occurs during phase 3 of a heart cell action potential?

Back 9

rapid efflux of K+ leads to repolarization

Front 10

describe what happens in all heart cells except the pacemaker cells during phase 4?

Back 10

a equal efflux of Na+ and influx of K+ keeps the cells interior at a steady negative state while replacing intracellular Na+ with K+

Front 11

describe what happens in the pacemaker cells during phase 4?

Back 11

efflux of K+ is reduced and a slow influx of Na+ causes slow membrane depolarization until the threshold is reached

Front 12

what are the fibers which carry electricle impulses tot he ventricles?

Back 12

Perkinje fibers

Front 13

do Perkinje fibers have fast or slow response action potentials?

Back 13

fast

Front 14

where are heart cells with slow response action potentials found?

Back 14

SA and AV nodes

Front 15

describe the two factors which determine action potential speed?

Back 15

amplitude of action potential (the lower the membrane potential the easier to create a action potential) and the rate of potential change (more channels open at once)

Front 16

what is the threshold for activation of Na+ channels?

Back 16

-70 mV

Front 17

what is the threshold for activation of Ca++ channels?

Back 17

-40 mV

Front 18

where are the pacemaker cells located?

Back 18

in the SA node usually

Front 19

what is the primary pacemaker should the SA node be damaged?

Back 19

the AV node

Front 20

what is the beat rate of the SA node?

Back 20

70-80 beats/min

Front 21

what is the beat rate of the AV node?

Back 21

40-60 beats/min

Front 22

if you see the ventricles contracting before the atria what has happened?

Back 22

the AV node has taken over pacemaking

Front 23

what is the last and final resort after both the AV and SA nodes no longer function as pacemakers?

Back 23

the Perkinje fibers take over and cause 30-40 beats/min... usually will not see atrial contractions, only ventricular

Front 24

how do the pacemaker cells in all of the different locations know when to take over pacemaking?

Back 24

the fastest firing pacemakers take take precedence thus when they fail the next fastest pacemaker takes over

Front 25

describe the conduction of the electrical impulse generated in the SA node to the whole heart?

Back 25

goes to the atrial muscle cells via the bachmann's bundle

travels to the AV node via 3 internodal fibers, from AV node it travels through the bundle of His to Perkinje fibers, Perkinje fibers distribute signal from central (intraventricular septum) to lateral and from endocardium to epicardium

Front 26

what is the conduction speed in the AV node?

Back 26

.05 m/s

Front 27

what is the conduction rate in the bundle of His?

Back 27

1-4 m/s

Front 28

what normally determines whether an impulse will pass throught the AV node?

Back 28

sympathetic (increases conduction) and parasympathetic (decreases conduction) stimulation

Front 29

what abnormal process can block electrical impulses through the AV node?

Back 29

infarct or other cellular damage

Front 30

describe the pathology of reentry arrythmias?

Back 30

impulses cannot travel in a anterograde direction in the heart, but still can loop back around in a slow retrograde fashion. For this to happen the heart must either be beating very slowly or the heart muscle cells must have an abnormally fast repolarization.

Front 31

what is the major cause of reentry arrythmias?

Back 31

ischemia in heart tissue leading to a high extracellular K+ concentration which causes depolarized membrane potentials and conduction block (slow heart beat)

Front 32

how do you fix the reentry arrythmias seen in tissue necrosis?

Back 32

you give lidocain which blocks Na+ channels which helps to repolarize the heart cells

Front 33

what is the result of a pH of 6.5 on the heart?

Back 33

it blocks calcium induced calcium release causing a reduction in cardiac muscle contraction

Front 34

what type of receptor does calcium bind to on the endoplasmic reticulum?

Back 34

a ryanodine receptor

Front 35

what are the 3 ways in which calcium can be removed from the cardiac muscle cells?

Back 35

1. sarcoplasmic reticulum calcium pump (ATP dependent)
2. sarcolemma calcium pump (ATP dependent)
3. sarcolemma 1 calcium / 3 Na+ exchanger (ATP independent)

Front 36

explain how the Ca++/Na+ exchanger pump can be used to treat congestive heart failure?

Back 36

drugs such as digitalis block Na+/K+ exchangers thus increase intracellular Na+ concentrations which reverses the direction of the Ca+/Na+ exchanger bringing more Ca+ into the cell causing muscle contraction