Cardiac physiology and ECG Flashcards
What is the purpose of desmosomes in cardiac muscle cells
allows the cardiac myocyte to cope with mechanical stress, e.g stretching
What is CICR?
Calcium-Induced-Calcium-Release
What is the funny current activated by?
Hyperpolaristaion
What is the resting potential of the cardiac myocyte cells?
-55mV
What channels lead to repolarisation?
Potassium channels
What is the refractory period?
A period where it is not possible to elicit a new action potential immediately regardless of how much the membrane is depolarised
Why do we need a refractory period in the heart?
So that the heart has enough time to fill in between contractions
What is the absolute refractory period?
The shortest possible time between two consecutive action potentials in a cell
What is the latent period?
time between initiation of an AP and the succeeding
contraction
What does the conduction system in the heart allow for?
Allows for propagation of a nervous impulse rapidly throughout the heart, also ensures there’s a delay in impulse conduction between the atria and ventricles
What is annulus fibrosis?
An electrical insulator that slows down transmission from the atria to the ventricles
What connects cardiac myocytes to eachother?
Intercalated discs
Why are gap junctions important?
they ensure the velocity and safety of propagation of impulse
What are some differences between the action potential of the SAN and a non-pacemaker cell?
Cardiac, -55mv, uses ‘funny channels’, slower rise
What type of cells have a brief refractory period?
skeletal muscle cells
Where would you place ECG’s?
Right and Left forelimb and Left hindlimb
Describe a first degree atrioventricular block
P waves are still present but there is a longer time period between P and R, hence there is a delay in the AV- this can be missed on traces and is usually not a cause for concern
Describe a second degree atrioventricular block
Multiple P waves fire without a QRS Complex, although the Pr interval still stays the same
Describe a third degree atrioventricular block
The atria and ventricles do not communicate with each other so the P wave and QRS wave are independent of each other
What is phase 0 of the cardiac action potential?
Depolaristaion of the membrane due to a strong but brief increase in the permeability of Na+
What is phase 1 of the cardiac action potential?
Na+ channels quickly reactivate causing the membrane to quickly repolarise
What is phase 2 of the cardiac action potential?
Repolarisation is halted due to the opening of voltage gated calcium channels which creates a plateau phase
What is phase 3 of the cardiac action potential?
Repolarisation begins with the opening of K+ channels
What is phase 4 of the cardiac action potential?
K+ channels are open and maintain a resting membrane potential
