Lecture 3 Flashcards
If a cell has a resting membrane potential, it means that it is what?
polarised
What is the resting membrane potential for a cell compared to the outside of the cell?
it is negatively charged
Does a cell have a high or low K+ permeability? What does this mean?
it has a high K+ permeability which means that K+ can easily flow out to keep the resting membrane potential negative
Does a cell have a high or low Na+ permeability? What does this mean?
it has a low Na+ permeability which means that it can’t enter easily to keep the resting membrane potential negative
Does a cell have a high or low Ca2+ permeability? What does this mean?
it has a low Ca2+ permeability which means that it can’t enter easily to keep the resting membrane potential negative
If a depolarisation reaches threshold, what does this cause?
an action potential
What is a conduction?
a depolarisation wave
At resting membrane potential, the inside of the cell is negatively charged compared to the outside of the cell. What happens when the cell depolarise?
this changes so the inside of the cell is positively charged compared to the outside of the cell
Where does the conduction system start in the heart?
at the pacemaker cells in the sinoatrial node
Where is the sinoatrial node located?
it is located at the top of the right atria (atria on the left of the diagram)
From the sinoatrial node, the depolarisation propagates down the atria to where?
the atrioventricular node
What is the purpose of the AV node?
to conduct the siganl from the atria to the ventricles
Where is the AV node located?
in the right atria, up against the boundary of the atria and the ventricles
At the border between the atria and the ventricles, you have the fibrocartilaginous tissue (valves). What do these act as and what does this mean?
these act as an insulator which means that an electrical signal cannot pass through this structure and go from the atria to the ventricles without going through the AV node
Once the signal moves through the AV node, we go through a structure known as the what? Where is this located?
bundle of His
adjacent to the annulus of the tricuspid valve, distal to the atrioventricular node, and slightly proximal to the right bundle branch and left bundle branch
After going through the bundle of His, where does the signal go?
It splits into the left and right bundle branches and travels down the septum to the heart to the apex
At the apex of the heart, where does the signal go?
It wraps up around the heart through the purkinje fibres and then into individual cardiomyocytes
How is the structure of the cardiomyocyte specialised for the conduction of action potentials?
Each cell is interwoven and branch at either end. There are intercalated discs with gap junctions to allow rapid ion flow between cels so that all the cells can interact and contract together in a functional syncytium
At what rate per minute is the SA node generating action potentials?
100 APs per minute
At what speed are action potentials conducted through the atrium?
0.5 ms-1
At what speed are action potentials conducted through the AV node?
0.05 ms-1
Why are action potentials conducted more slowly through the AV node than the SA node?
This delay allows full depolarisation and contraction of the atria before depolarisation and contraction of the ventricles
Why does the heart contract from the apex, upwards?
in order to push the blood upwards to the arteries to leave the heart
At what speed does the action potential spread through the ventricular myocardium?
0.5 ms-1
At what speed does the action potential spread through the bundle of His, bundle branches, Purkinje fibres?
5 ms-1
Why is the spread of action potential through the ventricular myocardium slower than in the bundle of His, bundle branches, Purkinje fibres?
because it allows synchronous depolarisation and contraction of all ventricular regions
The speed of conduction of the action potential spreads slowest in the what?
AV node
What are the two types of cells that conduct action potentials in the heart? Where are these located generally?
pacemaker cells (in the SA node)
follower cells (such as the cardiomyocytes in the apex of the ventricles, although it is the same diagram for the atria)
How many phases are there of the pacemaker cells in the SA node?
3
What are the names of the 3 phases in the pacemaker cells in the SA node?
4, 0, 3
Of the three phases of the pacemaker cells, what one reflects the “resting” membrane potential? Why is this in inverted commas?
This is phase 4
This is the pre potential phase 4 and the “resting” membrane potential fluctuates between -60mV and -70mV (so it is not really resting which is why is in inverted commas)
Why is phase 4 o a pacemaker cell not really resting?
It is unstable because of funny Na+ channels.
What is the effect of funny Na+ channels in the pacemaker cells?
they cause a slow influx of Na+ which means the MP increases which causes the unstable RMP