Lecture 13 - The Cardiac Action Potential And ECG Flashcards
What is the only conducting node in the heart
The AV node
What does the AV node introduce
A considerable delay to the spread of excitation
What have the AV node cells developed
Latent powers of rhythmicity and can take over pacemaking if impulses from the SA node fail to reach them
Where are pacemaker cells found
The SA node, AV node, Bundle of His and Purkinjie fibres
How many action potentials does the SA node produce per minute
70-80
How many action potentials does the AV node produce per minute
40-60
How many action potentials does the bundle of His and the Purkinjie fibres produce per minute
20-40
What can alter the SA node discharges
By parasympathetic and sympathetic stimulation
In pacemaker cells what causes depolarisation
The entry of Na+
What channels does the Na+ entry through
Fast Na+ channels
What is early depolarisation caused by
The closure of the fast Na+ channels
What happens in the plateau stage
The slow Ca2+ channels open while most of the K+ channels close
When does late depolarisation close
The Ca2+ channels close and the K+ channels open
What happens during the resting potential phase
The membrane potential remains more or less constant, but the ion distribution across the membrane is restored to its initial state
What does the P wave in an ECG represent
Atrial depolarisation
