Cardiac Resting Membrane and Action Potential Flashcards
Describe the sequence of electrical conduction in the heart.
Na+ influx leads to conduction -> SA node activation -> Atrial activation -> AV node activation -> His-Purkinje Bundle -> Ventricular activation -> Ventricular Contraction
How does hyperkalemia affect the resting membrane potential?
High extracellular [K+] will increase the resting membrane potential and depolarize the cell as a result. The inside of the cell retains more K+ ions.
How does hypokalemia affect the resting membrane potential?
The resting membrane potential is not changed much by hypokalemia due to two factors:
- Small Na+ influx that stabilizes the membrane potential
- Inward rectification as the permeability of K+ is decreased due to iK1 blocks that occurs as the driving force on K+ increases
How does the K+ permeability change with hyperkalemia?
It increases
How does the K+ permeability change with hypokalemia?
It decreases
What is inward rectification and when does it occur?
It is a decrease in K+ permeability that occurs when either the electrical or chemical driving force on K+ is increased.
1) Hypokalemia
2) Depolarization of the membrane
What is the range for hyperkalemia?
> 5 meq/L
What is the range for hypokalemia?
Less than 3 meq/L
What is responsible for the fast response of the action potentials?
Na+ Channels
What is responsible for the slow response of the action potentials?
Ca2+ Channels
K+ Channels (iK/iK1/iTO)
How can fast responses be converted into slow responses?
Fast responses can be blocked by a toxin such as tetrodotoxin which blocks Na channels. Only the slow channels like the Ca2+ channels are left unaffected. As a result, the fast upstroke disappears and only the slow Ca response remains.
Why is the LV thicker and stronger than the RV?
Systemic resistance is much higher than pulmonary resistance.
