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Bpk 305 > Initiation Of Cardiac Action Potential > Flashcards

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)
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2
Q

What initiates the cardiac action potential

A

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

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3
Q

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

A

Pacemaker channels called HCN channels (funny channels)

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4
Q

Describe pacemaker channels (HCN channel) structure and gating

A

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

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5
Q

What does HCN channel stand for

A

Hyperpolarization-activated, cyclic nucleotide gated channel

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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

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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
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8
Q

How many subunits does HCN channel have

A

4 subunits same as K+ channels

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9
Q

What is Ef value and what current is it for

A

Ef = -20 mV
Current is If= IHCN

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10
Q

What 2 channels are missing from SAN AP

A

Strong inward rectifier (Kir)
Na+ channel

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11
Q

When do HCN channels open

A

Turn on during repolarization, wind up hyperpolarizing membrane

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12
Q

What current causes the start of repolarization in SAN AP

A

Ik,DR

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13
Q

What current causes depolarization in SAN AP

A

ICa

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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

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15
Q

What does the parasympathetic system control

A

Rest and digest

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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
Q

What is the role of annulus fibrosis in the heart

A

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
Q

What is the role of the atrioventricular node

A

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
Q

In the electrical impulse conduction pathway, which step is the lowest? And why does it need to be the slowest?

A

Conduction through the atrioventricular node. Creates delay between atrial and ventricular depolarization

28
Q

How do purkinje fibres conduct action potentials so quickly?

A

Due to their low resistance. Caused by the combination of their wide diameter and their large number of gap junctions

Bpk 305 (10 decks)

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