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Define Automaticity
The ability of cardiac pacemaker cells to spontaneously depolarise and generate their own action potential
- This is due to the 'leak' of ions that slowly bring the membrane to threshold
Define Excitability
The ability of (all) cardiac cells to respond to (be excited by) an action potential
Define Conductivity
The ability of (all) cardiac cells to conduct an action potential
Define Contractility
The ability of cardiac myocytes to contract
What is the absolute refractory period
The period from when a membrane reaches threshold potential and depolarises, to when it repolarises past threshold potential
- During this time the membrane is absolutely unresponsive to stimuli (you can't bring it to threshold potential if it's already past it)
What is the relative refractory period
The period from when a membrane repolarises past threshold potential, to when it returns to resting potential
- During this time, the membrane is responsive only to strong stimuli
What is an ectopic beat
A beat originating from somewhere other than the pacemaker for the underlying rhythm
What is a premature ectopic and what causes it?
An ectopic beat occurring early in the cardiac cycle, normally caused by 'irritability' of the cardiac cells
What is an escape ectopic and what causes it?
An ectopic beat occurring late in the cardiac cycle, normally as part of the 'escape' failsafe mechanism when the pacemaker does not fire
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