Lecture 9 Flashcards
What is a cardiac conduction cell?
Has a pale and striated appearance with low actin and myosin
How much of all cardiac cells do the conduction cells make up?
1%
What is a cardiac contractile cell?
Had a striated appearance with high actin and mysin
How much of all cardiac cells do the contractile cells make up?
99%
Where does depolarisation begin?
At the sinoatrial node (SAN)
How does depolarisation spread?
Through the gap junctions of the intercalated disks
What is a gap junction?
Pores within the sides of the cells that has low ionic current resistance
In what direction does depolarisation spread?
In all directions because it can spread through both cardiac and contractile cells
What is a functional syncytium?
Many things behaving as one functional unit
What is the pacemaker of the heart?
The sinoatrial node
Where is the SA node located?
In the right atrium
Once an electrical signal has been conducted in the SA node, where does it spread to first?
The left atrium via the interatrial bundle pathway of conduction cells
Why does the electrical signal flow between atria first?
To allow simultaneous contraction of the two atria
How does an electrical signal get to the AV node?
Via the internodal bundles
Why does the electrical signal pause at the AV node?
To allow the atria to stop contracting before the ventricles contract
Where does an electrical signal go after the AV node?
To the Purkinje fibres via the bundle branches
Why does the electrical signal travel to the apex of the heart first?
For the highest efficiency contraction of the ventricles to push as much blood out of the heart as possible
What is quiescence?
When there is no electrical signal, the heart is fully repolarised
What are the steps of relaxation, depolarisation and repolarisation during heart contraction?
Initially at quiescence (all 4 chambers relaxed), excitation spreads from SA node, atria depolarise, atria repolarise and AV node sends excitation to ventricles, ventricles depolarise and contract, ventricles repolarise, heart fully relaxes again
What does an ECG detect?
Changes in polarisation state within the heart
What are the features of an ECG trace?
The P wave, QRS complex, T wave
What is the P wave?
Detection of depolarisation in the atria
What is the QRS complex?
Two things happening at once. Atria repolarising while ventricles depolarise
What is the T wave?
Detection of the repolarisation in the ventricles
What is the cause of the gap between the P wave and QRS complex?
The delay between atrial and ventricular depolarisation, caused by the AV node
Why is the QRS complex the largest wave on the ECG trace?
The ventricles contain the greatest amount of muscle so create a greater depolarisation
What part of an ECG trace is the lubb heart sound associated with?
The S wave - end of the QRS complex - ventricular depolarisation complete and isovolumetric phase begins so the atrioventricular valves close
What part of an ECG trace is the dupp heart sound associated with?
At the end of the T wave - ventricular repolarisation complete and the semilunar valves close
