CVS Physiology 2: Cardiac Electrophysiology And Excitation-contraction Coupling. Flashcards
List the 4 basic properties essential for the heart to function as the central pump?
1- autorhythmicity.
2- conductivity.
3- excitability.
4- contractility.
Definition: generating its own electrical impulse rhythmically.
Autorhythmicity.
Definition: ability to conduct electric impulse.
Conductivity.
Definition: ability to respond to stimuli by producing electrical action potentials.
Excitability.
Definition: a capacity for shortening in response to suitable stimulus.
Contractility.
Electrical impulses are generated and conducted in the _______.
Heart.
Excitation wave starts from _________ _______ (__ m/s), then to __________ ______ (__m/s), the to the ________ _______ (__ m/s), finally to ______ ____ ____ and ____ ____ _____ (__m/s).
Excitation wave starts from sinoatrial node (SAN) = (1m/s).
Then to atrioventricular node (AVN) = (0.05m/s).
Then to the atrioventricular bundle (AVB) = (1m/s).
Finally to:
Right bundle branch (RBB).
Left bundle branch (LBB).
(4m/s).
Which node is the dominant node?
SA node “pacemaker”.
Why does the AV node have a 100-msec delay?
Allows time for ventricular filling.
List the order of pacemaker rates?
SA > AV > bundle of His/purkinje/ ventricles.
List the order of the speed of conduction?
Purkinje > atria > ventricle > AV node.
List the 3 ions in the resting ventricular muscle cell?
1- K+.
2- Na+.
3- Ca2+.
What is the intracellular concentration of K+ in the resting ventricular muscle cell?
135 mEq/L.
What is the intracellular concentration of Na+ in the resting ventricular muscle cell?
10 mEq/L.
What is the intracellular concentration of Ca2+ in the resting ventricular muscle cell?
.0001 mEq/L.
What is the extracellular concentration of K+ in the resting ventricular muscle cell?
4
(Meaning it moves from intracellularly to extracellularly).
What is the extracellular concentration of Na+ in the resting ventricular muscle cell?
145
(Meaning it moves from extracellularly to intracellularly).
What is the extracellular concentration of Na+ in the resting ventricular muscle cell?
2
(Meaning it moves from extracellularly to intracellularly).
What is the equilibrium potential of K+ in the resting ventricular muscle cell?
-94 mV.
What is the equilibrium potential of Na+ in the resting ventricular muscle cell?
+70 mV.
What is the equilibrium potential of Ca2+ in the resting ventricular muscle cell?
+132 mV.
What is the permeability of K+ in the resting ventricular muscle cell?
High.
What is the permeability of Na+ in the resting ventricular muscle cell?
Low.
What is the permeability of Ca2+ in the resting ventricular muscle cell?
Low.
List the 3 main groups of membrane channels?
1- ungated channels.
2- voltage - gated channels.
3- ligand - gated channels.
Which membrane channel is concentration based?
And give an example?
Ungated channels.
E.g: K+ channel.
Which membrane channel is voltage dependent?
And give an example?
Voltage - gated channel.
E.g: Na+ channels, Ca2++ channels, K+ channel.
Which membrane channel is ligand (protein) dependent?
And give an example?
Ligand - gated channel.
E.g: acetylcholine gated.
What is the way of diffusion of ungated channels?
Passive diffusion.
List the 2 types of cardiac muscle fibers?
1- contractile fibers.
2- excitatory and conductive fibers (auto rhythmic cells).
What is the major cardiac muscle fiber?
Contractile fibers.
Which cardiac muscle fiber is responsible for the generation and conduction of the excitation wave of all parts of the cardiac muscle?
Excitatory and conductive fibers (auto rhythmic cells).
Which cardiac muscle fibers constitute the atrial and ventricular walls?
Contractile fibers.
Which cardiac muscle fibers is responsible for the pumping action of the heart?
Contractile fibers.
What do the excitatory and conductive fibers (auto rhythmic cells) include? (5)
1- SAN fibers.
2- AVN fibers.
3- bundle of His = A-V bundle.
4- Rt and Lt bundle branches.
5- purkinje fibers.
Definition: the intracellular potential of the resting cell?
Resting membrane potential (RMP).
What is the resting membrane potential (RMP) of a resting myocyte?
-90 mV.
In atria and ventricular cells, the resting membrane potential is _____, until ______ _____ is applied.
Stable until external excitation is applied.
In the SA node cells, membrane potential is ___ _____ and called as the ______ _______, always moving towards the ____ ____ with time.
Not stable and called as the pacemaker potential, always moving towards zero millivolts (mV) with time.
Definition: negative intracellular potential moves towards zero and then becomes positive.
Depolarization.
Give an example of depolarization?
Na+ or Ca2+ influx depolarizes cell.
Definition: negative intracellular potential is re-established after depolarization.
Repolarization.
Give an example of repolarization?
K+ efflux repolarizes cells.
What effect would increasing the extracellular K+ ion has? What is the net result?
Reduce the efflux of K+ ions or even create an influx of K+ ions, the net result will be depolarization.
What effect would decreasing the extracellular K+ ion has? What is the net result?
Accelerate the efflux of K+ ions, the net result of which will be hyperpolarization.
A cell’s resting membrane potential is very sensitive to change in what?
A change in extracellular K+ ions.
What is the response of cardiac action potential in ordinary myocytes?
Fast response.
What is the response of cardiac action potential in nodal muscle fibers?
Slow response.
Where does the fast response of cardiac action potential occur?
Occurs in atrial, ventricular muscles and purkinje fibers.
Where does the slow response of cardiac action potential occur?
Occurs in the SA and AV.
What is membrane potential of SAN?
SA has unstable membrane potential,
(-55:-60).
Which channels open and close with Low K and high Na? (Extracellularly)
Closure of K+ channels.
Opening of “funny” channels (Na+ channels).
Which channels open and close with high Ca?
Opening of voltage-gated Ca++ channels (transient, T-type channels).
Closure of funny channels.
Which channels open and close with high high Ca?
Opening of voltage-gated Ca++ channels (long, L-type channels).
Closure of T-type Ca++ channels.
Which channels open and close with high K and low Ca?
Opening of voltage-gated K+ channels.
Closure of voltage-dependent Ca++ channels (L-type).
List the 2 effects of parasympathetic stimulation?
1- hyperpolarize»_space; increasing conductance out of cell and decrease “funny current” (sodium) and calcium conductance.
2- decrease in the slope if pre potential»_space; takes longer to reach the threshold»_space; intrinsic firing decreases.
List the 2 effects of sympathetic stimulation?
1- activation of beta receptors»_space; increased “funny current” (sodium) and increased calcium influx.
2- increase in the slope of prepotential»_space; threshold is reached sooner»_space; intrinsic firing increases.
Increased Ca2+ premeability in cardiac myocytes has which effects?
Increased contractility and increased SV.
What happens in phase 0 of electrical activity?
Depolarization of the membrane to -65 mv leads to opening of fast Na+ channels, this causes rapid influx of Na+ ions.
What happens in phase 1 of electrical activity?
Brief repolarization caused by K+ efflux.
What happens in phase 2 (plateau) of electrical activity?
Balance between inward Ca++ and outward K+.
What is the importance of the plateau phase?
Important to maintain contraction for adequate time to empty the heart chambers.
What happens in phase 3 of electrical activity?
Rapid repolarization,
Causes:
1- inactivation of Ca++.
2- activation of outward K+ channels (delayed rectifier).
What happens in phase 4 of electrical activity?
Causes: continuous activation of outward K+ channels.
How long does the absolute refractory period lasts?
Lasts almost the entire time of one cardiac muscle twitch (one contraction).
What happens by the time the action potential and muscle contractions are fully over?
No tetany of cardiac muscle possible.
What happens when Ca++ ions enter the cardiac muscles?
Induces Ca++ release from sarcoplasmic reticulum.
The heart is a syncytium of many cells electrically connected at intercalated discs by _______ _______?
Gap junctions.
Cardiac muscle is _______ type and contain __ _____ and highly developed _______ ___ _______.
Striated type and contain T-tubules and highly developed intracellular SR networks.
_____ _____ provide the excitation stimulus used to activate plasma membrane Ca2+ channels causing a substantial ____ ______.
Action potentials.
Ca2+.
Ca2+ induces Ca2+ release (CICR) through which channel?
Ryanodine receptor channels (RyR).
What does local release of Ca2+ cause?
Causes calcium sparks.
Calcium ion binds to what to initiate contraction?
Troponin.
What occurs when calcium unbinds from troponin?
Relaxation.
Ca2+ is pumped back into SR for what?
Storage.
Ca2+ is exchanged with what?
Na+.
Na+ gradient is maintained by what?
Na-K-ATPase pump.
