Cardiac Conductance: Lecture 4/5 Flashcards
What is the order of myocontraction depolarization?
- Atria
- Ventricles
True or False
Each chamber does NOT contract at the same time, it uses waves of depolarization
True
What does the SA node stand for?
sinoatrial node
What does the AV node stand for?
atrioventricular node
What is the pacemaker of the cell?
SA node
Where does the depolarization start?
SA node
What are the steps in heart contraction?
- 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
Where do the ventricle contractions start?
from the bottom
True or False
The atrium fully relaxes and then the ventricles contract
True
True or False
The AV node slows down the wave of depolarization so the atria can fully contract before ventricular contraction
True
What is 1 cardiac cycle
Atrial excitation + Ventricular excitation + Ventricular relaxation
How long is the conduction of the AV node? relatively?
approx 0.1 seconds to a quarter second
What is the SAD node made of?
- bundle of cells
- kind of like a muscle and a nerve
- has action potential
- starts the wave of depolarization
The SA node can contract?
NAURR, it can depolarize
Intrinsic heart rate is what?
A self-excitatory system
Where does Pacemaker potential occur?
in the SA node
In a resting state is there more Na+ or K+ in the cells of the SA node?
K+
Is there Cl- in the resting cell of the SA node?
yessir
What is the resting potential of the cells in the SA node?
-60
What is the value of the threshold potential in cardiac SA node cells?
-40
Why is there an increase +20 slope from -60 to -40?
That is the pacemaker’s potential
What is the peak of an action potential in a SA node cell?
+1 to +5
What determines the action potential in SA node cells?
how quickly or slowly the pacemaker potential occurs, which will determine our action potential frequency for 1 minute
aka determines heart rate
If the Pacemaker slope is steeper, what will the heart rate be?
steeper slope = increased action potential frequency aka faster heart beat
What does decreased permeability refer to?
the channel is closing!!
Before we see any potential what is happening in a resting SA node cell?
- Decreased in K+ permeability
- K channel closes - Increased Na+ permeability
- via F-type channel
- small positive increases in membrane potential
- Increase in Ca2+ permeability
- via T-type channels (transient-type calcium channels)
- brings cell to threshold potential
Why are the T-type channels slow?
we want to make sure our heart rate is not too fast
At threshold what is occurring in the SA node cell?
- T-type Ca2+ channels close
- L-type Ca2+ channels open
*allows action potential to occur
What do L-type calcium channels allow for?
big and faster influx of calcium, called long-type calcium channels
What is happening at the peak of the action potential?
- Calcium channels close
- K+ channels open to repolarize the cell!
What changes in the cardiac action potential cycle as our heart rate goes up?
Pacemaker potential will most likely be steeper
True or False
The slope of the pacemaker potential will determine the rate of action potential generation aka the heartbeat
True
What is the main source of the action potential occurring in the SA node cells?
calcium concentration
How do we decrease our heart rate?
parasympathetic stimulation
How do we increase our heart rate?
sympathetic stimulaiton
The initial increase in heart rate starts from what?
the withdrawal of the parasympathetic stimulation
In the case without the SA node, will the AV node have its pacemaker rate? if so what will it be?
Yes, 25-40 action potentials per minute
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
True
Arithmia mean what?
when there is no unison/consistency in the SA node stimulating the AV node
How can we pace the ventricles if there is some sort of lost connection between the SA node and the AV node?
- pacemaker
How do pacemakers work?
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
