Lecture 21 Flashcards
What is the path of electrical conductance?
- SA node
- Internodal pathways
- AV node
- Bundle of His
- Right and Left bundle branches
- Purkinje fibers
T or F? Transmission through AV node is slower due to smaller fibers and fewer gap junctions.
True
What is the purpose of the delay through the AV node?
Allows atria to contract before the ventricles contract.
In the ____ ___ ____, conductance of action potential is very fast.
Bundle of his.
_____ node is natural pacemaker of heart.
Sinoatrial (SA) node
____ _____ is a specialized muscle tissue with no contractile proteins and connect directly to “regular” myocardial fibers of atria.
Sinoatrial (SA) node
T or F? Action potential that is generated in AV node travels immediately to atrial fibers resulting in atrial depolarization.
False, SA node not AV nodes
What does not require innervation by SNS to stimulate an action potential?
Fibers of SA Node fire action potentials in rhythmic pattern ~100 beats/min via self-excitation.
What is the mechanism of self-excitation of the SA node?
Fibers of SA node are leaky to Na+.
Is the resting membrane potential of the SA node higher or lower than that of other fibers?
Higher, (-55 mV) in comparison to other fibers (-90 mV)
What is the threshold of the SA node?
-40 mV
During rapid depolarization of autorhythmic cells, (phase 0), ____-type Ca++ channels are opened.
L-type (L = “longlasting”)
T or F? In autorhythmic cells, repolarization (phase 3) is the opening of K+ channels.
True
HR is set by the ____ _____.
Sinoatrial (SA) node
The rate and contractility of the heart can be regulated by the ______
ANS
How is the HR affected by the SNS?
Norepinephrine acts on the SA node to increase Na+ permeability, making the cell reach threshold faster. Increasing HR.
How is contractility affected by the SNS?
In cardiac myocytes, Norepinephrine increases intracellular Ca++ concentration which increases contractility. (Ventricles)
How does the PNS decrease heart rate and contractility?
Acetylcholine is released.
- Increases permeability to K+ causing hyperpolarization which decreases rate of SA node firing and decreases rate of excitability of A-V junctional fibers slowing transmission of impulse
- Decreases intracellular Ca++ in myocytes which decreases contractility
What is phase 0 of the action potential of contractile myocytes?
Depolarization, opening of Na+ channels
What is phase 1 of the action potential of contractile myocytes?
K+ channels open and Na+ channels inactivate
What is phase 2 of the action potential of contractile myocytes?
L-type Ca++ channels open. The outflow of K+ balances the influx of Ca++ causing the plateau in repolarization. The influx of Ca++ is responsible for the initiation of contraction.
What is phase 3 of the action potential of contractile myocytes?
Phase 3: more K+ channels open and Ca++ channels close
What is phase 4 of the action potential of contractile myocytes?
Na/K ATPase has in effect exchanged Na that entered in phase 0 for K+ that left in phase 2 & 3. Ca++ is exported via various Ca++ pumps
The absolute refractory period (ARP) is long lasting which prevents a development of a _____ contraction in the heart.
tetanic
T or F? Any failure of the heart to relax fully would make it an ineffective pump. The ability of the heart to relax is just as important as the ability of the heart to contract.
True
What are the abnormal pacemakers of the heart?
AV node (40-60 beats/min) Perkinje fibers (15-40 beats/min) Atrial or ventricular muscle tissue (~20 beats/min)
What is another name for abnormal pacemaker?
Ectopic pacemakers
What can result from ectopic pacemakers?
An ectopic pacemaker can result in an abnormal sequence of contraction.
What does an electrocardiogram (ECG or EKG)?
Records electrical activity within myocardial muscle fibers (not the conductive system)
T or F? An EKG records the electrical activity within the conductive system.
False, an EKG records electrical activity within myocardial muscle fibers (not the conductive system).
What does the P-wave represent?
Atrial depolarization
What does the QRS complex represent?
Ventricular depolarization ( ≤0.10 seconds) Q wave: first downward deflection (often not present) R wave: first upward deflection S wave: downward deflection following R wave
What does the T wave represent?
Ventricular repolarization
What does the P-Q or P-R interval (0.12-0.20 seconds) represent?
Time it takes from the beginning of P wave (atrial depolarization) to the beginning of QRS complex (ventricular depolarization)
What does the QT interval (<0.45 seconds) represent?
Time between beginning of ventricular depolarization and end of ventricular repolarization
What does the S-T segment represent?
The time between the end of ventricular depolarization and beginning of ventricular repolarization.
On an EKG paper, the X-axis represents time (sec), how many seconds is each small box and each larger box?
Small box = 1mm = 0.04 seconds
Large box = 0.20 seconds
On an EKG paper, the Y-axis represents the voltage (mV), how many mV is each small box and each larger box?
Small box = 0.10 mV
Large box = 0.50 mV
T or F? A wave of depolarization causes a wave of positive charges within the myocardial muscle fibers.
True
T or F? A wave of repolarization causes a wave of negative charges inside of myocardial muscle fibers in the opposite direction.
True
As a wave of ________ charge (depolarization) moves toward positive electrode, get an upward or positive deflection on EKG.
positive
If a wave of depolarization moves away from a positive electrode, you will get a ____ deflection on EKG.
downward (or negative); (in other words, if a wave of positive charges moves towards a negative electrode it results in a downward deflection)
A wave of negative charges moving towards a negative electrode results in a(n) _______ deflection.
upward
T or F? Wave returns to baseline when there is no difference in charge (complete depolarization or repolarization).
True
In a 12-lead EKG, what are the names of the 6 limb leads?
I, II, III, AVR, AVL, AVF
Which of the limb leads are biopolar?
I: right arm (-) to left arm (+)
II: right arm (-) to left leg (+)
III: left arm (-) to left leg (+)
Which of the limb leads are unipolar?
AVF: left foot (+) and both arm electrodes are common ground(-)
AVL: left arm is (+) and right arm & left foot common ground(-)
AVR: right arm is (+) and left arm & left foot common ground(-)
T or F? 6 chest leads (V1-V6): chest electrode is (+) and your back is (-), even though you are not placing an electrode on your back.
True
Which of the chest leads has the QRS mostly upward?
V6
T or F? Most of the chest leads are on the right side of the chest.
False, left side.
T or F? In the chest leads, your back is the negative chest leads.
True
