Lecture 21 Flashcards
Transmission through AV node is ______ due to smaller fibers and fewer gap junctions
Slower
True or false? Delay through AV node allows atria to contract before the ventricles contract.
True
Bundle of His conducts the action potential very fast or very slow?
Very Fast
Bundle of His is also know as what?
AV bundle
This is the natural pacemaker of the heart
SA Node
True or false? The SA node has contractile proteins
False
True or false? The SA node specialized muscle tissue
True
Fibers of SA node connect directly to what?
Regular myocardial fibers of atria
Action potential that is generated in SA node fibers travels immediately to atrial fibers and causes what to happen?
Atrial depolarization
The fibers of the SA node fire action potentials in rhythmic pattern of about 100 bpm via what mechanism?
Self-excitation
True or false? The fibers of the SA node are not permeable to Na+
False - the SA node fibers allow Na+ to leak in
True or false? Resting membrane potential of SA node is less negative in comparison to other fibers
True - resting membrane potential in SA node is -55 mV compared to -90 in other fibers.
- Depolarization up to threshold- mostly due to slow Na+ influx
- Rapid depolarization- opening of L(“longlasting”)-type Ca++ channels
- Repolarization- opening of K+ channels
Action potential of autoarythmic cell
Heart rate is set by the __ _______
SA node
_____ increases heart rate and contractility
SNS
_____ decreases heart rate and contractility
PNS
SNS releases what NT?
Norepinephrine
In SA node, Norepi _______ Na+ permeability, which increases restimg membrane potential, and increases rate of drift towards threshold
increases
In cardiac myocytes, Norepi _______ intracellular Ca++ concentration which _______ contractility
Increases, increases
Vagus nerve releases what NT?
acetylcholine
Acetylcholine release from Vagus nerve causes what?
Increase in permeability to K+, causing hyperpolarization
Hyperpolarization causes _____ rate of SA node firing and ______ excitability of AV jucntional fibers
Decreased, decreased
Hyperpolarization _____ intracellular Ca++ in monocytes, which decreases contractility
decreases
During exercise are you using SNS or PNS more?
SNS
At rest, are you using SNS or PNS more?
PNS
What is phase 0 of an action potential of a contractile monocyte?
Opening of Na+ channels
What is phase 1 of an action potential of a contractile monocyte?
K+ channels open and Na+ channels inactivate
What is phase 2 of an action potential of a contractile monocyte?
L-type Ca++ channels open
When does K+ outflow balance influx Ca++ causing repolarization plateau
When L-type Ca++ channels open
What is responsible for initiation of contraction?
Influx of Ca++ from L-type Ca++ channels
What is phase 3 of an action potential of a contractile monocyte?
More K+ channels open and Ca++ channels close
What is phase 4 of an action potential of a contractile monocyte?
- 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
This long-lasting period prevents development of a tetanic contraction
Absolute refractory period (ARP)
True or false? Any failure of the heart to relax fully would make it an ineffective pump.
True
True or false? The SA node is the only pacemaker of the heart.
False
AV node, Perkinje fibers, and atrial or ventricular muscle tissue are all ______ pacemakers
Abnormal or ectopic
________ can result in abnormal sequence of contraction
Ectopic (abnormal) pacemakers
This records the electrical activity within the myocardial muscle fibers
Electrocardiogram (EKG, ECG)
P-wave represents what part of the cardiac cycle?
Atrial depolarization
QRS complex represents what part of the cardiac cycle?
Ventricular depolrization
T-wave represents what part of the cardiac cycle?
Ventricular repolarization
P-Q or P-R interval represents what part of the cardiac cycle?
The rate of transmission through the AV node
Q-T interval represents what part of the cardiac cycle?
Time between beginning of ventricular depolarization and end of ventricular repolarization
S-T segment represents what part of the cardiac cycle?
Time between the end of ventricular depolarization and beginning of ventricular repolarization
X axis of EKG represents what?
time
Y axis of EKG represents what?
Voltage (mV)
A wave of depolarization causes a wave of ______ charges within the myocardial muscle fibers
Positive
Wave of repolarization causes a wave of ______ charges inside of myocardial muscle fibers
Negative
If a wave of charges is moving toward a like charged electrode, there will be an ______ deflection (ex: positive charge moving toward positive electrode)
Upward deflection
If a wave of charges is moving toward an opposite charged electrode, there will be an ______ deflection (ex: positive charge moving toward negative electrode)
Downward deflection
Leads I, II, III, AVR, AVL, AVF are which type of leads?
6 limb leads
Leads I, II, III are _____ leads
Bipolar leads – formed by two electrodes
AVR, AVL, AVF are ____ leads
Unipolar leads – only one electrode placed, the other is common ground (negative)
Leads V1-V6 are which type of leads?
6 chest leads
In 6 chest leads, chest electrode is ____ and the back electrode is ___
Chest is positive and back is negative
V1 QRS is negative or positive?
Negative
V5 and V6 will be mostly negative or positive?
Positive
