LECTURE 22 10/24/22 (LECTURE 12 SLIDES: THE NORMAL ELECTROCARDIOGRAM) Flashcards
According to Dr. Schmidt, what is the #1 reason why you don’t want to drive your car through standing water?
You do not want to destroy your transmission because it is on the underside of your vehicle. (08:31).
Aside from the risk of drowning and hydroplaning.
What is the Vrm of the:
SA Node
Ventricles
Purkinje Fibers
Vrm:
SA Node: -55 mV
Ventricles: -80 mV
Purkinje Fibers: -90 mV
(From Exam 3)
Does a caine derivative (lidocaine) affect an SA node’s action potential?
No. Caine derivatives block VG Na+ channels which are not involved in SA Node. (10:27)
SA node
phase 0 involves VG+ L-type Ca2+ Channels
phase 3 involves VG+ K+ Channel
Lidocaine will affect a fast response action potential like the ventricular myocytes.
Rank the permeability of ions in phase 4 in both nodal tissue and ventricular myocytes from least permeable to most permeable.
Calcium
Sodium
Potassium
(The rankings are the same in both tissues)
What does “i” stand for when talking about ion channels in the heart?
Current (12:58)
What is the derivation of Ohm’s Law?
“Voltage is equal to Current times some type of Resistance”
(V=I*R)
(13:20)
The parasympathetic nervous system will stimulate what kind of channel on the nodal tissue?
K+ Channel (ACh-activated) —Ligand Gated
(14:45)
The parasympathetic nervous system will release ACh NT and bind to muscarinic ACh-R which is a GPCR. The alpha subunit will move laterally and open up a K+ channel and cause an efflux of K+, reducing Vrm, thus decreasing HR.
What channel opens during phase 0 and closes by phase 1?
Fast VG Na+ Channel (15:45)
Crossword Puzzle: This term describes how fast a signal is sent from one cell to the next. (Rhymes with what a Yankauer does, 10 letters)
Conduction (16:10)
How many consonants are in the NT that binds to muscarinic ACh-R in the nodal tissue?
aCeTYLCHoLiNe
C,T,Y,L,C,H,L,N
(8 consonants)
What phase is the most important in conduction in ventricular myocytes?
What ion is responsible for this?
Phase 0, sharp upstroke d/t fast VG Na+ Channels opening. (16:00)
Sodium.
What will phosphorylate the L-type Ca2+ Channel in the heart?
What happens to the Channel?
PKA
L-type Ca2+ becomes more sensitive to depolarization and opening them early to get more Ca2+ into the cell.
(18:14)
What is the gating mechanism of L-type calcium channels on the myocytes.
Both Voltage Gated and Ligand Gated. (18:05)
It can be a VG ion channel d/t manipulation by the level of phosphorylation through PKA.
L-type Ca2+ Channels can be ligand gated because it is regulated by ligand mediated pathways. Beta agonist that can increase the activity of PKA.
What is another name for the “funny” channels?
What is so funny with these guys?
Hyperpolarization Cyclic Nucleotide Channels -HCN Channels (19:11)
They are activated by hyperpolarization whereas most VG ion channels are activated during depolarization.
What is the correlation between B-adrenergic agents and the HCN channels?
More Beta agonist means the HCN channels will be open wider. This will result in a faster diastolic depolarization (shorter phase 4) leading to an increase HR. (20:27)
What ions can pass through HCN/funny channels?
What is the gating mechanism of these channels?
Primarily Na+, but Ca+ and K+ can pass through as well. (CATIONS) (19:16)
Both Ligand and Voltage Gated (19:16)
Voltage Gated d/t hyperpolarization.
Ligand Gated b/c it is ligand mediated by beta agonist.
What causes the K-IR to close?
What phase does the K-IR have the highest permeability?
The K+ inward rectifying channels close during inward current. Influx of Na+ or Ca+.
Phase 4
(22:00)
What channels are always open or never closed in the myocytes?
Leaky Na+ Channels
Leaky K+ Channels
Leaky Ca2+ Channels
Sodium Potassium ATPase Pump
(20:38)
During what phase will the Inward Rectifying K+ Channel remain closed?
When will the Inward Rectifying K+ Channel begin to open?
K-IR is closed during Phases 0, 1, and 2 (21:44)
K-IR typically opens up at the end of phase 2 to help us get back to resting membrane potential. (21:49)
What channel contributes to blip of repolarization at phase 1?
What kind of gate mechanism is this channel?
Transient Outward K+ Channel (22:30)
Voltage Gated
When does the Delayed Rectifying Channel start to open?
What is the main purpose of this channel?
What kind of gate mechanism is this channel?
Opens during phase 0 and remains open throughout phase 4 (22:48)
This is a specialized K+ channel that helps reset the cell at the end of phase 3 for the fast action potential (23:03)
Voltage Gated
How fast do the Delayed Rectifying Channels open?
These channels are so slow that when they start to open in phase 0, they allow the entire plateau phase to occur before they are fully opened. (23:43)
What is the self-defense K+ Channel?
Why is it called that?
What kind of gate mechanism is this channel?
ATP Sensitive K+ Channel (25:32)
If there is ischemia in the heart, it would probably be best for the heart to slow down its metabolic rate to preserve the myocytes. (24:49). If there is there is decreased in ATP around the heart, this channel opens.
Ligand gated (Mediated by how much ATP is sensed, a low amount will cause the channel to open) (30:37)
If there is an affluent amount of ATP in the heart, what is the state of our ATP Sensitive K+ Channel?
The ATP Sensitive K+ Channel is Closed.
No Ischemia, plenty of ATP. (26:12)
What specialized K+ Channels are only ligand gated?
K+ ATP Sensitive Channel
K+ Acetylcholine-activated Channel
What specialized K+ Channels are only voltage gated?
K-IR Channel
K-TO Channel
K-Delayed Rectifier Channel
What specialized K+ Channel are both voltage and ligand gated?
None
How many specialized K+ channels were discussed in lecture for cardiac myocytes?
Five
K+ ATP Sensitive Channel
K+ Acetylcholine-activated Channel
K-IR Channel
K-TO Channel
K-Delayed Rectifier Channel
How many total types of K+ channels are involved in one cycle of a ventricular action potential?
Four (Answer needs to be verified)
- Leaky K+ Channels (always open/never closed)
- K-Delayed Rectifier Channel (opens in phase 0)
- K-TO (opens in phase 1 “blip repolarization”)
- K-IR (opens towards the end of phase 2, repolarize cell in phase 3, open in phase 4)
What two channels contribute to the flat plateau in phase 2 of ventricular myocytes?
- L-type Ca2+ Channel (calcium influx)
- Leaky K+ Channel (potassium efflux)
(29:15)
What makes the end of phase 3 and the very beginning of phase 4 in ventricular myocytes have the highest permeability to potassium?
During phase 3, the myocytes are repolarizing. We have 3 K+ channels experience K+ Efflux. (32:15)
K-IR Channels
K-Delayed Rectifier Channels
K-Leaky Channels
What is term for a contraction or force generated without overall shortening in the muscle?
How is this possible?
Isometric Contraction (35:26)
Microscopically, the actin and myosin are experiencing shortening and the Z-disc are coming closer together to generate force. The overall muscle does not change in length due to connective tissues and elastins that stretch out as sarcomeres shortens. (36:40)
A high CVP will correlate to more __________ on ventricular myocytes.
Stretch/ Preload / Passive Tension (44:21)
What condition did Dr. Schmidt describe when a heart is stretched out too much where you will have a decrease in active tension?
Dilated Cardiomyopathy from s/p heart attack. (Increase in preload, increase in stretch, increase in passive tension) (44:53)
What term describes a contraction that involves using the same load, but under varying degrees of stimulation?
Isotonic Contraction (47:44)
What are the two ways the nervous system can generate more force out of a skeletal muscle?
Recruitment of more Motor Units
(Quantal Summation)
Increasing the Frequency of Stimulation -Hertz (Temporal Summation)
(47:24)
The action potential of the heart is initiated in the SA node and causes the atrial heart muscle contraction. What is the function of the delay in the AV node?
How long is this delay?
The AV nodal delay is there to allow the ejection to finish in the atria before ventricular contraction. (49:42) There is also a delay so that the heart can have a coordinate contraction (57:00).
0.09 seconds (52:40)
What part of the conduction pathway in the heart will set off the ventricular depolarization?
End of the Bundle of His (49:50)
What is another name for the Bundle of His?
AV bundle
What is the result of conduction of action potential through the septum and ventricular walls?
Ventricular Muscle Contraction (50:23)
How long does it take for an action potential to reach the far left lateral wall of the atria from the SA node?
0.09 seconds (51:14)
What will send the action potential conduction into the left and right ventricles?
Left and Right Bundle Branches (51:53)
How long into the action potential of the heart does the conduction system reach the right and left bundle?
0.16 seconds (52:35)
How long does it take for the AP to go from the SA node to the AV node?
0.03 seconds (53:00)
Where is the last place in the heart to depolarize and how much time does it take to get there from the SA node?
Lateral part of the left ventricle.
0.22 seconds (53:26)
How much time does it take to conduct an action potential in the ventricles only?
What is contributing to this rapid conduction?
From the beginning of the two main bundle branches to the last part of the left lateral ventricle is 0.06 seconds. (53:40)
Purkinje Fibers (wide cells chockablock full of gap junctions, larger the diameter, the lower the resistance) (54:20)
How many times faster is the ventricular conducting system than the atrial and bundle branch conducting system?
2.67 times faster.
.16 (atrial+ bundle branch conduction time) / 0.06 (ventricular conduction time) = 2.67
Explain the two causes of the delay in the atrial conduction system.
- AV Node: Few gap junctions results in slow conduction.
- Bundle of His: Also contain few gap junctions and narrow diameters that slows down conduction.
Both these contribute to the “electrical speed bump” in the atrial conduction. (56:00)
