electricity and the heart Flashcards
define electrical potential
energy stored in an electric field per unit charge
define voltage
energy required to move a particle from one place to another per unit charge
what 2 factors support movement of ions forming an electrochemical gradient
charge and concentration
during resting potential, what ion is the cell membrane relatively leaky to
potassium
which ion channel is mainly responsible for creating a concentration gradient
sodium potassium channel
3 Na+ out 2K+ in
define equilibrium potential
voltage required to maintain the concentration gradient
why does the inside of the cell generally have a negative electric potential form
it has impermeable negatively charged ions such as phosphate
the movement of positive ions can be enough to change the membrane potential
this can be enough to open voltage gated sodium channels and start an action potential
o
compare the time taken for a cardiac and neurone action potential
cardiac = 300msec
neurone = 1msec
what are pacemaker cells
specialized myocardial cells in atria with an intrinsic ability to depolarize rhythmically and initiate an action potential
automatic firing
SA AND AV NODES
what pump do the SA nodes have to help stimulate an action potential
sodium-potassium atp pump
how do pacemaker cells create an action potential
- sodium potassium atp pump in the node which uses ATP to traansport 3 NA+ OUT the cell and 2 k+ IN the cell
- during that there is additionally leaky potassium pumps pushing K+ out the cell slowly so the resting potential of the cell is around -55mV
- the nodes are also leaky to sodium and calcium
- calcium is concentrated outside of the cell and so the leaky channel causes calcium to leak into the cell and channels also cause sodium to leak into the cell
- because there are positive ions leaking into the cell, it causes the gradual drifting of depolarisation
- once the threshold voltage of -40mV is hit, this stimulated the opening of another calcium channel (but this one brings calcium into the cell quickly)
- this generates a fast stimulus up to around +20mV
- at +20mV more leaky potassium channels open causing heaps K+ to leak out of the cell
- this makes the voltage drop (repolarisation) to around -45/60mV
then the whole thing continually repeats
how many beats per min does the SA node make
60-100
how does the sympathetic system affect cell action potential
the leaky/slow Na+ channel permeability increases causing the steeper depolarisation of the beginning of the action potential (where the leaky calcium and sodium enter)
making the threshold reached faster and action potential hit faster so faster heart rate
how does the parasymstem affect cell action potential
leaky sodium channel permeability decreases causing less sodium entering the cell
beginning depolarisation trough is lowered and becomes flatter
threshold is slower to be met and this decrease rate of action potential / heart rate
under normal conditions the atria and ventricles are electrically insulated from one another
in what direction does the bundle of his occur from
right to left
which does depolarisation happen to first, the epicardium or endocardium
endocardium to epicardium
which action potential is shorter, epicardium or endocardium
epicardium
depolarisation and muscle contraction are not simultaneous
how can you tell theres atrial fibrillation via ECG
the spacing between the QRS are irregular and theres a lack of clear p-wave
can cause stroke
what is ventricular fibrillation and the issues it brings
chaotic and disorganised depolarisation of ventricles
cardiac output is severely reduced and rhythm is incompatible with life
patients put into cardiac arrest and need immediate defibrilisation
what is defibrilation
external electrodes apply current that simultaneously depolarises all cells in heart (so normal electrical acitvity can continue)
what is aystole
hearts electrical system fails causing your heart to stop pumping
