Cardiovascular system 6 Flashcards
What is a defining physical feature electrical (conduction) cells
‘Pale’ striated appearance - due to low actin and myosin
Why is there less actin and myosin in electrical cells
Electrical signal is conducted using Ca2+ molecules - the same signal used to activate contraction. In the absence of this a signal can travel
How does the signal get conducted
Depolarisation starts at sinoatrial node and spreads to neighbouring cells (Both conduction and contractile)
How does the signal spread
Through intercalated disks
What are intercalated disks
Connect most cells of the heart.
Contain gap junctions - pores with low resistance to ionic current (especially calcium)
What is a syncytium
A cytoplasmic mass containing several nuclei, formed by fusion of cells.
What is Quiescence
When nothing is electrically happening in the heart - Passive filling is occurring
What are the three waves of an ECG
P wave
QRS complex
T wave
What does and ECG measure
The electrical change within the heart (depolarising and repolarising)
What happens during the P wave
Atria depolarise (Initiated by SA node)
What happens after the P wave
The atria is fully depolarised - there is no change and it will be a straight line
What happens during the QRS complex
The atria start to repolarise at the same time as the ventricles start to depolarise
What happens after the QRS complex
The atria are fully repolarised and the ventricles are fully depolarised. There is no change and it will be a straight line
What happens during the T wave
Ventricles start to repolarise - stating at apex
What happens after the T wave
The ventricles are fully repolarised and there is a straight line
What is the sinoatrial (SA node)
The pacemaker - Small bundle of cells that tell the heart when to beat
What are the paths the conduction pathway takes from the SA node
Internodal bundles - Takes to AV node
Interatrial bundle - Takes to left atrium to start contraction
What does the Atrioventricular (AV node) do
Receives signal from SA node and puts a hold on it - this is so the atria can contract before the ventricles
What are the paths the conduction pathway takes from the AV node
Once atria are relaxing sends message into the AV bundle to the bundle branches - gets carried down the interventricular septum to the apex of the heart
What is the final step in the conduction pathway
Purkinje fibres connect to all contractile cells receive the message and start contraction from the apex of the heart
Why does contraction start at the apex of the heart
To try and squeeze out as much blood from the ventricles as possible (think of tube of toothpaste)
