Cardiac Conductance: Lecture 4/5

Question 1

What is the order of myocontraction depolarization?

Answer 1

1. Atria
2. Ventricles

Question 2

True or False
Each chamber does NOT contract at the same time, it uses waves of depolarization

Answer 2

True

Question 3

What does the SA node stand for?

Answer 3

sinoatrial node

Question 4

What does the AV node stand for?

Answer 4

atrioventricular node

Question 5

What is the pacemaker of the cell?

Answer 5

SA node

Question 6

Where does the depolarization start?

Answer 6

SA node

Question 7

What are the steps in heart contraction?

Answer 7

• SA node depolarizes and sends an electrical signal through the gap junctions of the cardiac tissue a wave of depolarization
• This wave of depolarization is going to cause action potentials through the right and left atria to make them contract at the SAME TIME
• Action potential will also reach the AV node and will send the wave of depolarization to the bundle of hiss and it goes down the right and left bundles to the bottom of the heart
• Once at the bottom of the heart the signals go to the Purkinje fibres and then they distribute the electrical wave to the muscles in the ventricles to cause ventricle contraction
• Once the ventricles re-polarizes that is the end of 1 heart beat and then the cycle repeats

Question 8

Where do the ventricle contractions start?

Answer 8

from the bottom

Question 9

True or False
The atrium fully relaxes and then the ventricles contract

Answer 9

True

Question 10

True or False
The AV node slows down the wave of depolarization so the atria can fully contract before ventricular contraction

Answer 10

True

Question 11

What is 1 cardiac cycle

Answer 11

Atrial excitation + Ventricular excitation + Ventricular relaxation

Question 12

How long is the conduction of the AV node? relatively?

Answer 12

approx 0.1 seconds to a quarter second

Question 13

What is the SA node made of?

Answer 13

• bundle of cells
• kind of like a muscle and a nerve
• has action potential
• starts the wave of depolarization

Question 14

The SA node can contract?

Answer 14

NAURR, it can depolarize

Question 15

Intrinsic heart rate is what?

Answer 15

A self-excitatory system

Question 16

Where does Pacemaker potential occur?

Answer 16

in the SA node

Question 17

In a resting state is there more Na+ or K+ in the cells of the SA node?

Answer 17

K+

Question 18

Is there Cl- in the resting cell of the SA node?

Answer 18

yessir

Question 19

What is the resting potential of the cells in the SA node?

Answer 19

-60

Question 20

What is the value of the threshold potential in cardiac SA node cells?

Answer 20

-40

Question 21

Why is there an increase +20 slope from -60 to -40?

Answer 21

That is the pacemaker’s potential

Question 22

What is the peak of an action potential in a SA node cell?

Answer 22

+1 to +5

Question 23

What determines the action potential in SA node cells?

Answer 23

how quickly or slowly the pacemaker potential occurs, which will determine our action potential frequency for 1 minute

aka determines heart rate

Question 24

If the Pacemaker slope is steeper, what will the heart rate be?

Answer 24

steeper slope = increased action potential frequency aka faster heart beat

Question 25

What does decreased permeability refer to?

Answer 25

the channel is closing!!

Question 25

Why are the T-type channels slow?

Answer 25

we want to make sure our heart rate is not too fast

Question 26

At threshold what is occurring in the SA node cell?

Answer 26

- T-type Ca2+ channels close - L-type Ca2+ channels open *allows action potential to occur

Question 27

What do L-type calcium channels allow for?

Answer 27

big and faster influx of calcium, called long-type calcium channels

Question 28

What is happening at the peak of the action potential?

Answer 28

- Calcium channels close - K+ channels open to repolarize the cell!

Question 29

What changes in the cardiac action potential cycle as our heart rate goes up?

Answer 29

Pacemaker potential will most likely be steeper

Question 30

True or False The slope of the pacemaker potential will determine the rate of action potential generation aka the heartbeat

Answer 30

True

Question 31

What is the main source of the action potential occurring in the SA node cells?

Answer 31

calcium concentration

Question 32

How do we decrease our heart rate?

Answer 32

parasympathetic stimulation

Question 33

How do we increase our heart rate?

Answer 33

sympathetic stimulaiton

Question 34

The initial increase in heart rate starts from what?

Answer 34

the withdrawal of the parasympathetic stimulation

Question 35

In the case without the SA node, will the AV node have its pacemaker rate? if so what will it be?

Answer 35

Yes, 25-40 action potentials per minute

Question 36

True or False In a normal healthy person, the AV node has its own pacemaker but is stimulated by the SA node for unison heartbeats

Answer 36

True

Question 37

Arithmia mean what?

Answer 37

when there is no unison/consistency in the SA node stimulating the AV node

Question 38

How can we pace the ventricles if there is some sort of lost connection between the SA node and the AV node?

Answer 38

- pacemaker

Question 39

How do pacemakers work?

Answer 39

they will have an external body machine with wires that go into the heart, in the right atria and ventricles to stimulate the cardiac tissue, acting as the SA and AV node

Question 40

What are the full steps of an action potential in the pacemaker cells?

Answer 40

The cell begins at -60 mv 1. K channels are closed - making cells more positive as K cannot leave - F-type Na channels open depolarizing - T-type Ca channels open depolarizing 2. Pacemaker potential is met at -40mv action potential now occurs: - triggers L-type Ca channel to open - a big influx of Ca into the cell - all other channels close - cell reaches 0 3. Cell restores resting membrane potential - K channels open again - L-type Ca channels now close