Cardiac electrophysiology Flashcards
What are the two types of muscles?
conducting-pacemaker cells. coordinate contraction contractile-cardio myocytes
what are the two types of action potential and their location?
slow -SA and AV fast -artial muscle, purkinje fibers, ventricular muscle
what is the rise time?
initial change in the membrane potential, initially as a fast as nerve cell, but have a long plateau
what are the fast AP current?
0=Na influx 1=repolarization via K channels 2=prolonged plateau via L-TYPE Ca CHANNELS 3=Ca channels close and remaining K resets the membrane potential 4=reseting membrane potential
is there a refractory period for fast or slow AP?
Fast -absolute refractory period lasts from phases 0-2 -volrage gated Na channels need to be reset before second AP can be fired
slow -refractory period due to opening of the K channel and resetting of the Ca channels
what are the slow AP currents
0=Ca current rather than Na 1&2=not seen 3=fast due to K 4=use HCN channel (hyper polarization activated cyclic nucleotide gated channel a)this is the location of the funny current b)depolarizes to the thresh hold point of voltage gated sensitive Ca channels
Which cells are faster? What sets the heart rate?
SA>>AV SA node
pacemaker and contractile cells have what between them?explain its function
gap junctions a)conduction- synchronized allowing appropriate timing, via pathway. this determines the “shape” of contraction b)coupled together-keep the cells in=phasic, synchronously.
refractory period
the time the heart cannot respond fast-the Na channels need to reset slow-K channels are open and Ca channels are resetting
what assures the conduction of the signal from one site vs another?
coupling
where does the AP start in the atria vs ventricles during contraction?
atria=base ->apex ventricles= apex->base
How does the SNS and PSNS have on the heart? what are the receptors
SNS- B1 adrenergic, positive chronotropic, dromotropic and inotropic effects PSNS-M2 muscarinic receptor(ACh) negative chronotropic, dromotropic and minor negative inotropic effect
what causes the plateau in fast currents?
Calcium
what causes depolarization in fast and slow currents?
K
explain the following with reference to the SNS and PSNS of the heart 1-chronotropic 2-dromotropic 3-inotropic
1-chronotropic= heart rate changes ( 2-dromotropic=conduction velocity changes 3-ionotropic=changes in strength in contraction SNS- positive affect for all three: increasing heart rate, increasing velocity of contraction and increasing strength of contractions PSNS-negative affect for chronotropic and dromotropic. slight negative for ionotropic
what affect does PSNS have on the chronotrpic effect? Dromotropic effect? inotropic?
chronotropic Ach-
- 1= reduces I-f in SA = longer phase 4
- 2=reduce I-k in SA = shifting resting membrane potential toward a more negative value(hyper polarization?)
- 3=reduces I-ca in SA = longer phase 4. Shift threshold value to a more positive value.
dromotropic 1=ACh
- slows conduction- making it longer for one cell to polarize another
very weak inotropic affect
Where does the PSNS have the greatest effect, AV or SA node?
SA node, b/c this node drives the heart. the AV node is affected by the AV node, but the SA node sets the sets the heart rate.
Which locations contain the slow conducting and fast conducting cells?
Slow= SA and AP Fast=purkinje fibers, atrial muscles, ventricular muscles
how do catecholamines affect the chronotroptic effect? dromotropic affect?
the heart rate is manipulated by catecholamines by a)increasing the I-f in the SA node= shorter phase 4(higher frequency) b)shift threshold value to a more negative value c) increase resting membrane potential by reducing I-k dromotropic a)these current changes all affect the dromotropic affect, velocity of the beats increases
what needs to change in order for the negative/positive affect to be achieved on chronotropic, dromotropic and ionotropic effect?
negative= 1- PSNS- all by ACh a)reduce currents of the “f” and “ca” b)increase current of “k” positive a)increase currents of “f” and “ca” b)decrease current of “k”
Describe what is happening during each phase of the slow AP. explain the two ways that calcium enter the cytoplasm.
0=Influx of Na causes depolarization. activating the voltage sensitive L-type Ca channels on the sarcolemma begin to open
1=K begins to flow out and Na channels close
2=Ca channels open. Also, the calcium induced calcium channel release channel on the SR
3=Ca channels close. K repolarizes the Vm to rest
4=cell is at resting membrane potential
There are two Ca channels - both sources of
1) Ltype voltage sensitve L-type Ca channel on the sarcolemma (extracellular)
2) CICR channel on the sarcoplasmic reticulum (intracellular)
what is the majority of the energy produced by in cardiac muscles?
aerobic metabolism, an abundance of mitochondria
how many times does a cardiomyocyte contract per heart beat?
how do catecholamines affet the myocardiocytes?
once!
unlike skeletal muscle, which recruit more cells (since all cells are recruited each contraction), cardio cytes increase heart beat via INOTROPIC MODULATION(Ca modulation)
inotropic modulation
- catecholamines=
- increase current of Ca, via L-type channels.
- this increases force
- increase CICR
- inducing greater Ca
- increase SERCA
- increase reqequestration activity
- increase affinity of troponin to Ca
- increase current of Ca, via L-type channels.
What are the 3/4 things that are modified by catecholamines in regars to Ca flux in cardiomyocytes?
Ca increase
1-Ltype channels open= increase extracellular Calcium
2-CICR increase = increasing intracellular calcim levels
3-SERCA activity increases = faster resequestration of the
4=increase affinity of troponin C to Ca
Deflection on ECG corresponds to…
Depolarization of the atria/ ventricles
repolarization of the venctricles
describe the events at each segment of the ECG. which interval gets shorter with heart rate?
P=indicative of the SA serving as the pacemaker. Length indicates atrial depolarization.
Pwave=depolarization of the artial muscles
PR=conduction thru AV node and to ventricles
QRS=duration tells us how fast the depolarization spreads throughout the ventricles
QT=interval releals how long the ventricles remain depolarized. gets shorter with increasing heart rate.
Twave=repolarization of both ventricles
describe the starling law and how it applies to cardiomyocytes
sarcomere length where the troponin and myosin overlap determines the contraction force. There is much more fiver around the heart that resists contraction
1- tension is built up very quickly b/c of connective tissue
what is EC coupling?
the process of increasing the inotropic affects on the heart via the L-type and CICR channels. increasing the Calcium channels increase the contracile force…
- what delivers the parasympathetic projections to the heart and where do they influence?
- compare to sympatheticvagus
- vagus
- SA and AV nodes
- sympathetic
- cardiac muscle
sympathetic and parasympathetic operate through what receptors?
sympathetic-B1
PARASYMPATHETIC= M2
