The excitable heart Flashcards
What is an electrical cell?
Small proportion, 1%, of our heart cells are electrical, very pale striated appearance and low levels of actin and myosin as they’re not contracting e.g. AV nodal cells and Purkinje cells
What is a contractile cell?
Most, 99%, of our heart cells are contractile, lots of actin and myosin and has a striated appearance e.g. working myocardial cell
What is a Sinoatrial Node (SAN)?
Sinoatrial node has the ability to generate spontaneous depolarisation hence it is where depolarisation begins. This signal (depolarisation) spreads to neighbouring cells (don’t need nerves to spread signal around heart) conduction cells are much faster than nerves at transferring signals to neighbouring cells. Increase cytosolic Ca2+ level when depolarisation reaches a muscle cell, activates cross-bridge attachment and contraction occurs
What are gap junctions?
Gap junctions allow charged particles (ions) to move between cells which allows current flow between adjacent cells. This allows depolarisation to pass through neighbouring cells quickly
How do gap junctions spread impulse?
Along conduction pathways, between electrical and contractile cells, between contractile cells
Increased speed of impulse throughout the heart, millions of cardiac cells behave as one - functional syncytium
Conduction pathway : SA node (sinoatrial)
Action starts in SA node and spreads very rapidly within the right atrium and the interatrial bundle connects the right and left atrium so that whenever something occurs in the SA node (which is essentially located in the right atrium) it will activate the left atrium very quickly as well
Conduction pathway : Internodal bundles
The entry way to the atrium and ventricles is the AV node (atrioventricular node) which receives information from the internodal bundles which passes signal from atria to ventricle
Conduction pathway : AV node (atrioventricular)
AV node conduction is quite slow causing a hold up so that the atria can contract and relax before we start to contract ventricle
Conduction Pathway : AV bundle and branches
The AV bundle spreads the signal from the AV node down to the apex right up into walls of myocardium so that all of the right and left ventricle can be activated essentially simultaneously
Conduction pathways : Purkinje Fibres
Purkinje fibres are ventricular contracting fibres that deliver depolarisation around the ventricle causing ventricular contraction
Excitation and conduction pathways
Quienscene ends as excitation spreads from SA node -> depolarises atria -> repolarises atria AV node sends excitation to ventricles -> atria relax then ventricles depolarise -> ventricles repolarise -> ventricles relax and the heart is back to quiescence
Quienscene means quiet/nothing
What is are leads in relation to ECG’s?
Leads are two electrodes that have a virtual line that can detect changes in voltage and the difference between the two electrodes. Can detect when the heart is depolarising and when it is repolarising
Excitation and conduction pathway ECG
Depolarisation by SA node, P wave occurs (electrical changes in atria). Atrial depolarisation complete, impulse delayed at AV node. Ventricular depolarisation begins at apex causing QRS complex (electrical change in both atria and ventricles). Atrial repolarisation occurs. Ventricular depolarisation complete. Ventricular repolarisation begins at apex causing T wave (electrical change in ventricles). Ventricular repolarisation complete
