Initiation Of Cardiac Action Potential Flashcards

1
Q

What determines action potential propagation

A
  1. Difference in voltage between cells
  2. Resistance between cells
  3. Threshold for AP firing
  4. Size of the cells
  5. Expression level of voltage-gated Na channels (depolarization phase)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What initiates the cardiac action potential

A

Sino-atrial node (SAN) found in roof of right atria

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What kind of channels does the sino-atrial node have?

A

Pacemaker channels called HCN channels (funny channels)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe pacemaker channels (HCN channel) structure and gating

A

-Structure similar to K+ channel
- non selective cation channel
- gated by cAMP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does HCN channel stand for

A

Hyperpolarization-activated, cyclic nucleotide gated channel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

State the pathway of electrical conduction in the heart

A

Sino-atrial node -> atrio-ventricular node -> bundle of his -> bundle branches -> purkinje fibers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does the SA node action potential compare to the ventricular muscle action potential

A
  1. Slower upstroke velocity- b/c lack Na+ channels. Depolarization occurs by ICa
  2. Reduced plateau duration- caused by ICa inactivation after upstroke
  3. Diastolic depolarization- causes voltage dip below resting potential of SA node. This is due to pacemaker HCN channel. Note diastolic depolarization doesn’t occur in myocytes
  4. Higher resting potential- b/c lack IK1 which maintains the resting membrane potential
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How many subunits does HCN channel have

A

4 subunits same as K+ channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is Ef value and what current is it for

A

Ef = -20 mV
Current is If= IHCN

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What 2 channels are missing from SAN AP

A

Strong inward rectifier (Kir)
Na+ channel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When do HCN channels open

A

Turn on during repolarization, wind up hyperpolarizing membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What current causes the start of repolarization in SAN AP

A

Ik,DR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What current causes depolarization in SAN AP

A

ICa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does sympathetic and parasympathetic stimulation effect diastolic depolarization slope

A

Sympathetic- increases diastolic depolarization slope, increase AP frequency
Parasympathetic- decreases diastolic depolarization slope, decreases AP frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does the parasympathetic system control

A

Rest and digest

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does the sympathetic system control

A

Fight or flight. Stress, danger, physically active

17
Q

Which HCN transmembrane segment (domain) binds cAMP

A

6

4 segments that span 1-6 transmembrane domains

18
Q

How does the concentration of cAMP change with sympathetic stimulation?

A

CAMP concentration increases, due to more noradrenaline release (NA). This allows HCN channels to open sooner and pass a larger current (If).

19
Q

How does the concentration of cAMP change with parasympathetic stimulation?

A

cAMP concentration decreases because acetylcholine (ACh) release acting on muscarinic 2 receptors causes a decrease in cAMP production (receptor inhibits adenylyl cylase (AC) reaction with ATP to produce cAMP)

20
Q

What reaction produces cAMP

A

Adenylyl cyclase + atp = cAMP

21
Q

How does sympathetic and parasympathetic stimulation shift the current vs voltage graph

A

Sympathetic- shift right
Parasympathetic- shift left

22
Q

What does stimulation of the cardiac vagus nerve do

A

Causes heart rate to slow down.
We notice changes in Ca2+ entry and changes in cAMP

23
Q

How does aerobic training affect vagal tone (vagus nerve) and in turn heart rate

A

Vagal tone increases, heart rate decreases

24
Q

Features of the atrio-ventricular node

A
  1. Smaller cells
  2. Fewer gap junctions
  3. Slower intrinsic diastolic depolarization rate (slows conductance)
  4. More negative Em
25
What is the role of annulus fibrosis in the heart
Acts as an insulator so that electrical impulses don’t travel another way through the heart. Specifically stops signals from going straight to ventricle using most direct route.
26
What is the role of the atrioventricular node
Coordinates contraction of the chambers so that the atria and ventricles don’t contract at the same time. Allows one chamber to contract as the other one fills
27
In the electrical impulse conduction pathway, which step is the lowest? And why does it need to be the slowest?
Conduction through the atrioventricular node. Creates delay between atrial and ventricular depolarization
28
How do purkinje fibres conduct action potentials so quickly?
Due to their low resistance. Caused by the combination of their wide diameter and their large number of gap junctions