Cardioviscular Physiology 2 Flashcards
What is the conduction system?
-Group of cells important in starting and spreading AP -> leading to the heart contracting
-they are connected to muscle cells through gap junctions
Order of cardiac conduction system
AP spreads from SA node (right atrium) –> AV node –> Bundle of his -> left and right Bundle branch -> AP goes down to the apex -> and ends at the Purkinje fibers
What is a pacemaker?
in the sinoatrial node, top of the right atrium
initiates the AP and spreads to AV node
What is the consequence of an AP in the SA node?
Contraction of the atria and pushing blood downwards to the ventricles
What happens when the AP arrives at the AV node?
There is a delay (AP arrives slowly), allowing the ventricle to get filled with blood before contraction (triggered by AP)
What happens when AP arrives at Purkinje fibers in the ventricles?
Purkinje fibers are connected to muscle cells through gap junctions -> spreading of AP leads to contraction in the ventricles
What is the backup pacemaker
The AV node, but it initiates AP more slowly and the heart rate will be slower
Action potential on ventricular muscle cell
Triggered by AP of SA node
-> Na enters rapidly through rapidly opening voltage-gated sodium channels causing rapid depolarization
-> Ca enters slowly via an L-type channel on T-tubules causing a long-lasting plateau phase where it stays depolarized + K channel close ensure depolarization
-> opening of voltage-gated K channels -> K goes out causing repolarizing to resting
Where are L-type channels located?
T-tubules
How are cardiac muscle cells connected?
Through intercalated discs - anchor and allow passage of ions
Desmosomes: structural anchors muscle cells together
Gap junctions: functional junctions, allow cardiac muscle cells contract together
atrial cells are connected to each other and SA node through gap junctions
ventricular cells are connected to Purkinje cells through gap junctions
Why is the heart muscle considered a syncytium (unit)?
Because atrial cells contract together and ventricles cells contract together
What role does the nervous system play in heart contraction?
The heart is self-excitable (automaticity), but the rate of contraction can be regulated by automatic NS
-> Sympathetic: increases HR
->Parasympathetic: decrease HR
How does cardiac contraction work?
Similar to skeletal muscles: L type channels: Ca binds to Troponin -> Tropomyosin shifts -> Myosinhead binds to actin
Explain the refractory phase due to long-lasting! Ca channels!
Long-lasting channels cause long lasting plateau phase, where we can’t fire another AP, which ensures relaxation after contraction of the heart, no tetanus (constant tension of the muscle)
Action potential within pacemaker (SA node)
Funny F-type Na channel: they open at resting potential, usually we need to get at threshold -> Na comes in
Triggers opening of T-type Ca channel: they are transient, they open and close very quickly -> Ca comes in -> takes us to the threshold
at threshold: Long-lasting Ca channel open -> Ca comes in, depolarization phase - SA AP
then L-type closes and voltage-gated K channels open -> K goes out causing repolarization to rest
