Lecture 21: Electrical Activity of the Heart/Intro to 12-lead EKG Flashcards
How does the SNS increase HR?
Norepi increases Na+ permeability
Excessive PNS stimulation can stop the heart. How?
acetylcholine increases K+ permeability
Phase 2 of the contractile cell (ventricular myocyte) action potential is due to what?
opening of Ca ++ channels
What tells you something about the rate of transmission through the AV node?
P-R/ P-Q interval
What would be most specific as to the rate of ventricular depolarization?
Width of the QRS
What tells you something about how long it takes for the ventricles to contract and relax?
Q-T interval
Why is transmission through the AV node slower?
due to smaller fibers and fewer gap junctions
What does the delay through AV node allow?
allows the atria to contract before the ventricles contract
What is the natural pacemaker of the heart?
SA node
Does the SA node have contractile proteins?
No it does not
Fibers of the SA node connect directly to what?
regular myocardial fibers of atria
Where does the AP that is generated in the SA node go and what does it lead to?
it travels immediately to the atrial fibers and leads to atrial depolarization
Fibers of SA node fire action potentials in what type of pattern?
rhythmic pattern of about 100 beats/min via self excitation
Describe the mechanism of self excitation of the SA node (3)
- Fibers of SA node leaky to Na+
- Resting membrane potential less negative (-55mV) in comparison to other fibers (-90)
- causes resting potential to creep up toward threshold (-40mV)
what effect does the SNS have on HR and contractility?
increases it
