Cardio: electrophysiology and contraction of muscles Flashcards
Major role fo potassium channels (Ik) in cardiac myocytes
repolarization pahse in all cardiac myocytes (determined by a series of K channels that open and close at various times)
how is the baseline maintained in cardiac myocytes?
“inward rectifying K+ current” IK1 - pumps- pumps K out of the cell at or near resting potential to maintain stability
desmosome
attachment site for cytoskeleton
“Trigger” Ca
the calcium that enters the cell through t-tubules in order to bind ryanodine and cause more calcium release from the SR
during the depolarization stage of cardiac myocyte action potential which channels open (and when)
Rapid sodium influx results in the sharp rise. L-type (slow) calcium channels open at -40 and start to cause a slow and steady influx of calcium (L-type remain open) . T-type calcium channels open at -50 and then close quickly. The Na channels then close as the voltage approaches membrane potential and we move to phase 1
define refractory period
deminsished capacity to respond to a stimulus
Describe phase 2 of the cardiac myocyte action potential
IT01 closes at the end of phase 1 but other potassium channels remain open (k out) and offset the influx of Ca - results in the plateau stage
Ventricular intercalated discs
end to end connection, integrates electormechanical function between cells
myocte triad
T-tuble and lateral sacs of sarcoplasmic reticulum
Starlings law (the quick and dirty)
The more you stretch the heart ( increase preload/amout of blood entering) the stronger the force contraction (to a certain point) Ex: faster pitch in baseball - you can hit it further
Relationship between gap junctions and conduction
more gap junctions = more rapid conduction
Major role of calcium channels (Ica) in cardiac myocytes
Contributes to atrial and ventricular depolarization and contraction (L-type and T-type)
Preload
passive tension prior to muscle contraction - determined by the state of stretch (volume of blood in the ventricle just prior to contraction= end diastolic volume EDV)
importance of the myocardial connective tissue matrix
interconnects myoctes and blood vessels, structural support of the heart, prevents damage by limiting stretching during diastole (due to overfilling), major pathway for force transmission across the heart, determines resting tension (ventricular diastolic pressure), “Holds” vessels open during contraction to limit the impact of surround pressure
which channel is responsible for the change seen in phase 1 of cardiac myocyte action potential
IT01 opens and is responsible for the early repolarization
The heart is made up of two electrical ____ connected by ______
the heart is made up of two electrical syncitium connected by unidirectional conduction through the AV node
Supranormal or Dangerous period
breif period of tue at the end of relative refractory when ANY stimulus (even subthreshold) can generate an action potential resulting in abnormal activation or arrythmias
which phases of the cardiac myocyte action potential are absolute refractory
Phase 1 and Phase 2
when the ___ gate is closed the cell cannot respond to a stimulus no matter how great the intensity
h gate
Main differences between Cardiac and Skeletal Muscles -
All cardiac cells function in conduction, some function to produce force (working Myocytes), Automaticity, smaller and shorter than skeletal mucle, GAP JUCNTIONS, contained within a connective tissue matrix that supports its function of a pump
which principle (law) represents the ventricles ability to increase stroke volumbe with increased preload in the heart
Frank-Starling Law of the Heart
Effect of increasing preload on contractility
NONE!! Increasing preload will increase force generation (frank starling) but with NOT change the contractility (remember: contractility is the ionotropic state of the heart)
sodium channel gates in the absolute refractory period
Phase 1 and 2 - m gates open and h-gates closed
Isovolumic contraction
tension is developed in the myocardium by there is no change in ventricular volume
