Cardiac contraction Flashcards
What does the SA node do?
spontaneously generates electrical potentials
Explain the pattern of conductance
SA node starts, activity goes rapidly to AV node, slow depolarization across the atria (conduction slows across the AV node), Rapid depolarization across the ventricle via the AV bundle. Depolarization spreads upward from the apex via the purkinjee fibers.
In health, do ventricles spontaneously depolarize?
No
Phases of ventricular action potential
know
What are the effects of the parasympathetic nervous system on the heart?
Decrease HR, Decrease conduction velocity, Decrease the excitability of latent
pacemakers.
Ex: Acetylcholine
Symapthetic activity effects on the heart?
Increase HR, Increase conduction velocity, Decrease the threshold of Calcium channels
Ex: Norepinephrine
What is the sequence of events regarding action potentials, intracellular calcium levels, and contraction
An action potential occurs, Intracellular calcium levels rise, contraction occurs
Strength of contraction is regulated by what?
Intracellular calcium levels during action potential
Initial strength of cardiac finbers which determines sensitivity to calcium
Intracellular calcium regulation
Cacium influx into cells
Calcium release from SR
Calcium uptake by SR
Calcium efflux
Catecholamines do what>
Accelerate the rate of cardiac contraction
Intracellular calcium decline
Cardiac relaxation
The greater the sarcomere length, the greater the contraction
true
Increased pre-load equals
inc stroke volume
How does the inc in length lead to increased cardiac force
A fast response to stretch, involving increased calcium sensitivity of myofibrils generated by stretch
A slow response to stretch involving activation of calcium channels by stretch
Basically, increasing length increases calcium sensitivity
What does the vagus nerve deliver to the heart?
parasympathetic innervation
What determines preload
End diastolic volume
