CVS 1 Flashcards
(14 cards)
Describe the heart’s autorhymicity
The heart contracting rhythmically as a result of action potentials it generates itself
What are the two types of cardiac cell
Contractile: - Do not normally initiate APs
Autorhythmic: -Do not contract, initiate and conduct APs
Describe the activity of cardiac auto rhythmic cells
They do not have a resting membrane potential, but display pacemaker activity
Pace maker activity is an autorhythmic cell membrane’s slow drift to threshold
Autorhythmic cells cyclically innate APs which spread through the heart to trigger contraction without any nervous stimulation
Name the four sites where specialised non-contractile cells demonstrate autorhythmicity
- SA node
- AV node
- Bundle of his
- Purkinje fibres
What dictates the rate at which contractile cells contract?
The SA node since the cells of the heart are linked electrically, so the rate of the fastest will be the rate of all, and it fires APs most frequently
What can alter the SA node discharge frequency?
Parasympathetic and sympathetic stimulation
What are the functions of the AV node?
- It forms the only conducting pathway between the atrial muscle and the bundle of his and hence the ventricles
- It induces a considerable delay to spread of excitation. This allows time for blood to move from the atria to the ventricles
- AV node cells have well developed latent powers of rhythmicity and can take over pace making if impulse from the SA node fail to reach them
What does an ECG measure?
The overall spread electrical activity across the heart at any time
What the P wave on an ECG show?
Atrial depolarisation
What the PR segment on an ECG show?
AV nodal delay
What the QRS complex on an ECG show?
Ventricular depolarisation (atria are depolarising simultaneously)
What the ST segment on an ECG show?
Time during which ventricles are contracting and emptying
What the T wave on an ECG show?
Ventricular repolarisation
What the TP interval on an ECG show?
The time in which ventricles are relaxing and filling
