Origin and Conduction of Cardiac Impulse Flashcards Preview

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Flashcards in Origin and Conduction of Cardiac Impulse Deck (57)
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1

What is the heart?

Electrically controlled muscular pump which sucks and pumps blood

2

Where are the electrical signals which control the heart generated?

Within the heart

3

What is autorhythmicity?

Heart is capable of beating rhythmically in the absence of external stimuli

4

Where does excitation of the heart normally begin?

Pacemaker cells in the sinoatrial node
Clusters of these cells initiate the heart beat

5

Where is the SA node situated?

Upper right atrium close to where superior vena cava enters the right atrium

6

What does the SA normally do?

Drives the entire heart rate (sets the pace)

7

What does it mean if a heart is in sinus rhythm?

Heart controlled by sino atrial node

8

Role and characteristics of cells in SA node?

No stable resting membrane potential
They generate regular spontaneous pacemaker potentials

9

What happens when a spontaneous pacemaker potential is generated?

It takes the membrane potential to a threshold and every time a threshold is reached an action potential is generated

10

What does an action potential being produced result in?

Generation of regular spontaneous action potentials in the SA nodal cells

11

Permeability to K+ in pacemaker cells?

Does not remain the same between action potentials

12

Pacemaker potential?

Slow depolarization of membrane potential to a threshold

13

Pacemaker potential?

Slow depolarization of membrane potential to a threshold

14

What does pacemaker potential look like on a diagram?

It is the beginning of a slight incline between two rises (-60mV->-40mV)

15

What does pacemaker potential look like on a diagram?

It is the beginning of a slight incline between two rises (-60mV->-40mV)

16

Ionic basis for a pacemaker action potential?

Once the threshold is reached:
-The rising phase (depolarization) of action potential is caused by activation of long-lasting L type Ca++ channels
-Resulting in Ca++ influx
-The falling phase (re-polarization) is caused by inactivation of L-type Ca++ channels and
-Activation of K+ channels resulting in K+ efflux

17

What is threshold?

-40mV

18

General description of how cardiac excitation spreads through heart?

starts at SA node
Passes by cell to cell conduction to get to the AV node
Then travels to the Bundle of His
then down the left and right branches
and to the purkinje fibers

19

Cell to cell excitation via GAP junctions?

From SA node through both atria
From SA node to AV node
Within ventricles

20

What is the AV node?

Bundle of specialized cardiac cells located at the base of the right atrium just above junction of atria and ventricles

21

What is special about AV node?

ONLY point of electrical contact between atria and ventricles

22

Spread of excitation across atria?

Mainly cell to cell via gap junctions

23

Spread of excitation from SA node to AV node?

Mainly cell to cell conduction via gap junctions but also some inter-nodal pathways

24

What happens to conduction in AV node?

It is delayed - this allows atrial systole (contraction) to precede ventricular systole

25

What do Bundle of His and Purkinje fibres allow?

Rapid spread of action potential to the ventricles

26

Spread of excitation across ventricular muscle?

Cell to cell conduction

27

Action potential in contractile cardiac cells and pacemaker cells?

Differ considerably

28

Resting membrane potential of atrial and ventricular myocytes?

-90mV until excitation

29

Depolarization of myocytes? and it's name

- Caused by fast Na+ influx
-Rapidly reverses membrane potential to +20mV
-Phase 0 of AP in contractile cardiac muscle cells

30

Phases of ventricular muscle AP?

Phase 0- fast influx of Na+
Phase 1- Closure of Na+ channels and transient K+ efflux
Phase 2- Mainly Ca++ influx
Phase 3- Closure of Ca++ channels and K+ efflux
Phase 4- Resting membrane potential