Origin of the heartbeat Flashcards
The heart muscle is composed of two major cell types - what are these?
- contractile cells (majority of heart cells) = straited
- non-contractile cells with unstable membrane potentials (autorhythmic cells) = aid in electrical conduction
Membranes of non contractile cells depolarises slowly until it reaches a threshold value to generate what?
- generates an action potential
Once an action potential has been generated (after slow depolarisation of non-contractile cell membranes) what happens to the action potential?
- Action potential spreads through cellular gap junctions causing contraction of contractile cells
Where is the primary pacemaker region?
- the sinoatrial node (SA node)
The SA node has the fastest rate of depolarisation why?
- sets pace of heart
Pacemaker activity can be regulated by what?
- can be regulated by autonomic NS
What does the heart not need to contract?
- doesn’t need nerves to contract as it has an intrinsic contraction
What is the cardiac skeleton?
- fibrous connective tissue NOT bone
What does the cardiac skeleton provide?
- provides rigidity and site of attachment for musculature and values
The cardiac skeleton electrically insulates each chamber meaning it needs what for AP propagation?
- wiring for AP propagation
What is the wiring for the AP propagation?
- the conduction system
The SA node spontaneously depolarises - resting heart rate does what between species?
- varies
Autorhythmic cells form a specialised conduction system what does this system allow for?
- faster conduction than possible through gap junctions
- introduce an important delay from atria to ventricles
List the order of conduction through the heart?
- SA node
- Atrial muscle
- AV node
- Bundle of HIS
- Purkinje fibres
- Ventricular muscle
The membrane of the SA node is what?
- unstable
How does the SA function as a pacemaker - describe what happens within the node?
- gradual and slow depolarisation of the membrane potential
- reaches threshold potential triggers rapid depolarisation (action potential)
- action potential in SA node terminated
- gradual depolarisation and drift back towards threshold potential
- these repeated slow depolarisations are called pacemaker potentials
Describe the pattern of a membrane potential (this would be shown on a graph):
- Gradual depolarisation (becomes more positive)
- peak of depolarisation and termination
- repolarisation (becomes more negative)
- starts again
Cell membranes keep ions at different concentrations internally vs externally.
A difference in charge across the membrane does what to it?
- polarizes it
Most animal cells have a stable … what resting membrane potential?
- a stable negative resting membrane
= inside is negative compared to the outside
If ions were allowed they would diffuse .. their concentration gradient
- if ions were allowed they would diffuse down a concentration gradient
if more ions were diffusing in then out of a cell what would happen?
- depolarisation
If more ions were diffusing out a cell than in what would happen?
- repolarisation
What would sodium moving into the membrane do?
- depolarise
Ca moving in would do what to the membrane?
- depolarise