A&P Test 4 Flashcards
When you have depolarization going from left to right, what kind of deflection would you expect?
Positive
If you have repolarization going from left to right (the same way as depolarization) what kind of deflection would you expect?
negative deflection
When we have repolarization going from right to left, (opposite of depolarization), what kind of deflection would you expect?
a positive deflection
(double negative)
what is another name for phase 4 in the slow action potential?
diastolic depolarization
the faster the rate of diastolic depolarization the faster the __________ will be
heart rate
What is phase 0 due to in the slow action potential?
Slow L type ca++ channels
slow to open and stay open longer than fast Na+ channels
The slope of Phase 0 is really important in determining what in the heart?
How fast an ap is going to propagate around the heart
what is the slope of phase 3 due to in the slow AP?
L-type Ca++ closing and VG K+ channels opening
Is there a phase 2 in slow action potentials?
Possibly. This depends on the textbook/article. Most leave it out
Is there a phase 1 in slow action potential?
no!
In the AV node, what is the VRM?
more negative than the SA node
Are there HCN channels in the nodal tissue?
yes, highest density in the SA node but there are some in the AV node as well
AP in the ventricular endocardium start _______ AP’s in the epicardium, and the ventricular endocardium tissue is repolarized ________ AP’s in the epicardium.
before
after
repolarization happens in the ventricular epicardial tissue before the repolarization is _____ in the ventricular endocardial tissue
complete
Why is it important to have the more superficial tissues in the heart contracting at the same time as the slower subendocardial tissues?
What does this idea explain?
Because we want a coordinated contraction and efficient ejection
it explains why the ventricular endocardial AP is longer than the ventricular epicardial AP. So the inside and outside of the heart is contracting at the same time.
The atria action potential looks different from nodal tissue and ventricular APs in what way?
the 0 slope is very steep (pretty much straight up an down) the plateau phase is shorter, and the AP in the atrial epicardial tissue and atrial endocardial tissue look the same (bc the atria doesn’t have to pump against a lot of force)
Kind of looks like a mix between a slow action potential and a fast action potential
How long (in seconds) does it take for the SA node to self depolarize and generate an action potential?
.83 seconds
60 seconds in a minute
=72bpm
without any input from the sympathetic chains or vagus stimulation, how fast would the SA node AP be?
110 beats per minute
If you have a normal amount of sympathetic nervous system in a heart rate without vagus stimulation, how fast would the heart rate be?
120
If you have a normal amount of vagal stimulation and you remove the sympathetic stimulation from the heart, how fast would the heart rate be?
60-62 BPM
Which has the most effect on the heart rate ? sympathetic or vagal
vagal
What is the secondary pacemaker?
AV node
If the AV node was the pacemaker of the heart, how fast would your heart rate be?
40-60BPM
If the Purkinje fibers became the pacemaker of the heart, how fast would your heart rate be?
15-30 BPM
what are the purkinje fibers?
The conduction tissue in the ventricles that are buried within the muscle mass
If the timing and order of the electrical system in the heart doesn’t happen the right way, what happens?
muscle tissue that is active or inactive at the wrong time = inefficient heart. Can lead to decrease in BP.
The conduction system of the ventricles are called the
perkinje fibers
The conduction system of the atria are called the
internodal pathways
how many internodal pathways do we have? what are they called?
3
anterior (closest to the left atrium)
middle
posterior
Where are the internodal pathways found?
Right atrium
What ensures that the L atrium gets electrical activity from the SA node?
Interatrial bundle
where does the Interatrial bundle/Bachmann’s bundle come from?
the anterior internodal pathway
How long does it take for an AP to go down the internodal pathway and arrive at the AV node?
.03
3/100
seconds
how long does it take the entire right atria to depolarize under normal conditions?
.07
7/100
seconds
how long does it take the left atria to completely depolarize under normal conditions?
.09
9/100
seconds
What is the P wave?
How long is the P wave?
A graph showing the depolarization of both atria
.09
9/100
seconds
Why does it take so long (.09 sec) for an AP to get to the lower lateral part of the left atrium?
because we don’t have any specialized tissues to conduct action potentials so AP have to go through myofibrils which have a bunch of “stuff” in them clogging up the pathway
In a perfectly healthy heart, the AP can get from the SA node to the last piece of ventricle muscle in what amount of time?
0.22
22/100
seconds
what causes the delay in an AP going from the AV node to the farthest part of the ventricles?
What is the physiological purpose of this?
Fat blob around the AV node
a lack of gap junctions
We want a delay so that the ventricles have time to fill before contracting
The atria sometimes acts as a filter and filters out
errant AP hitting the AV node during a refractory period
how long is the delay at the AV node?
0.12 seconds
what is the bundle of his?
the area that is located just upstream from the two main bundle branches. Between the atria and ventricles at the septum
How long is the delay at the bundle of his?
0.01 seconds
what is the total time it takes for an AP to go from the SA node to each of the main bundle branches?
0.16 seconds
what is the total delay from the AV node to each of the main bundle branches?
0.13 seconds
how long is PR interval?
0.16 seconds
List the order and times of action potentials from the SA node to the top of the interventricular septum.
SA Node
.03 secs
AV node
0.12 seconds
Bundle of His
0.01 seconds
interventricular septum
what helps to protect us from Ventricular tachycardias that originate in the atria?
The AV node
If you have a + electrode on the left foot and a - electrode on the right arm, you would expect to see what type of deflection during depolarization?
positive
what is the angle of the average electrical movement during a typical heart beat?
59 degrees
If the deflection on the EKG is taller than normal, you can assume there is ______ tissue for the AP to cross over.
more
like hypertrophy or the tissue is stretched out
Which part of the heart is completely depolarized during the QT interval? which part may be repolarized before the end of the QT interval?
the deeper parts of the heart
the more superficial part of the heart
if we were to put the electrodes closer to the heart, you would expect what?
a larger deflection of depolarization on the EKG
(like you see in V1-V6)
what does the QT interval correspond to?
the length of time that we have depolarization happening the ventricular tissue.
at the beginning of the EKG you have no ________.
why?
deflection. the Heart is at rest.
what do you see on an EKG when the SA node generates an AP?
a P wave
how big is the P wave? (in boxes)
2.5 boxes wide
2.5 boxes tall
If the P wave started at the AV node and traveled retrograde, what kind of deflection would you see?
negative
If you have an inverted P wave, what is happening?
the AP is starting in the wrong place
what causes an exaggerated (high) p wave?
something wrong with the right atria.
usually Hypertrophy, sometimes it is stretched out
if the p wave is too long, what is happening?
it is a conduction problem stemming from something happening in the L atrium
(if the L atrium is all stretched out)
if the height of the p wave is a problem it is d/t a problem with the _______ atrium
right
“height right”
If the length of the p wave is a problem, it is d/t a problem with the ________ atrium
Left atrium
“long left”
if there is a really big problem in the left atrium, what might you see?
a double hump in the p wave
d/t an electrical block preventing the AP from spreading correctly to the L atrium
what is the q wave?
a negative deflection before the r wave
what is the r wave?
a positive deflection showing depolarization of the ventricles
do all leads have a q wave?
no
what is the pr interval?
the time between the P (initiation of an AP in the atrium) and R (initiation of an AP in the ventricles) wave
Because we don’t always have Q waves it is not called the PQ wave
how long is the pr interval?
0.16 seconds
what is the s wave?
a negative deflection after the r wave?
how long should a QRS be?
0.06 seconds ideally
typically it is longer than this in real life
what is the magnitude of the QRS complex?
the total electrical activity during the QRS complex
1.5 mV
if we have a QRS that is really tall, what is happening?
- electrodes might be placed really close to the heart
- the heart tissue is bigger than normal (enlargement of the ventricles)
What makes a QRS complex longer than normal?
enlargement of the ventricles (makes EKG deflection tall and long)
dilated cardiomyopathy( more stretched out)(just makes the EKG deflection long)
What is at the end of the QRS complex?
What is going on here?
J or Isoelectric point
when all of the ventricular muscles mass has been electrically excited and is now depolarized
If we have an injured portion of the heart, what would you expect to see at the J-point? After the T wave?
The injured and healthy heart tissue to be depolarized
After the T wave you would expect to see the healthy tissue repolarized and the injured tissue to still be depolarized. (it is unable to get enough energy to repolarize)
what is the source of an odd tracing between the T and next P wave?
the injured cells sending out new AP
what do we compare the repolarized portion of the EKG to when the repolarized portion is showing abnormal currents?
repolarized portion of EKG= time between the T wave and P wave.
the J-point
What is the QT interval?
How long is the QT interval?
What else could you call this?
The time between the beginning of ventricular depolarization to the end of ventricular repolarization.
The 0.25-0.35 seconds
The duration of the fast action potential in the endocardium
what is the ST segment?
What does this segment tell us?
the period of time between the end of the S wave and start of the T wave
periods of injury, ischemia, and infarct.
what is the T wave?
upward deflection showing repolarization of the ventricles spreading from epicardial layers to endocardial layers.
repolarization moving retrograde of depolarization making it a positive deflection. (double negative=positive)
if you have a physiologic increase in HR, (being active) what will shorten in the EKG?
- ST segment
QT interval ( because the ST segment is a part of the QT interval) - The time between the end of T wave and the beginning of the P wave
what is a positive Lusitropy agent?
Something that repolarizes the ventricle faster than it normally does by shortening the ST and QT intervals.
what is Inotropy?
more Ca+ coming into the heart and being released from the SR. Makes for a stronger contraction
what is Chronotropy
refers to the HR
what is Dromotropy
speed of conduction of the AP. Entirely dependent on Na+ current.
(more Na+ = faster the hr)
what is the R-R interval?
the time between the 2 adjacent QRS complexes
what is the formula for a hr based off an EKG?
60seconds/0.83 (R-R interval)= 72BPM
Big boxes on an EKG is how many mV?
0.5mV
Small boxes on an EKG is how many mV?
0.1mV
5 small boxes in 1 big box
Before modern electronics, paper was sent though a machine and a pen would draw out EKG’s to be spit out on the other side.
How fast was the movement of the paper, and how is this still pertinent to us today?
25mm of paper per 1 second.
Today our EKG’s are measured in a period of 1 second, being separated out by 5 big boxes and 5 small boxes within that.
=25mm
what percentage does one big box represent on an EKG?
what percentage does one small box represent on an EKG?
0.2 seconds
0.04 seconds
Each small box moving horizontally is how many seconds?
0.04 seconds
What kind of experiments did Smidt do in labs that used paper EKGs?
goat experiments
In research, you’re supposed to keep all records of your research for how long?
as long as you’re in business
what is the refractory period?
the time after an AP when the heart is resetting itself. If you were to stimulate a heart cell during this time, you probably wouldn’t see an AP at all or you might see a premature AP that is smaller than normal.
if we don’t allow the cell to reset all the way, what period are you in?
the relative refractory period
not all the way reset
can you get an ap during the relative refractory period?
yes but it won’t be very strong and the pumping action of the heart will take a hit. It will show up as a small depolarization
as long as we wait for the heart to completely reset, you can create an AP ________
Earlier than normal
what is the absolute refractory period?
when the cardiac muscle hasn’t reset enough to generate an new AP at all.
Why isn’t there much of a slope in phase 4 of a fast action potential of the ventricle?
There aren’t many HCN or leaky sodium or Ca++ channels in the ventricles.
what has a greater slope during phase 4, a fast or slow action potential?
slow action potential ( has more HCN channels)
how does the slope of phase 0 in a slow AP compare to the slope of phase 0 in a fast AP?
Why?
It is less steep in a slow AP
Fast AP phase 0 is just about straight up and down because fast Na+ channels are involved
spell the alternate name for the interatrial bundle
Bachmann’s bundle
