electricity and the heart Flashcards
concentration of calcium in the plasma ( extracellular )
2
conc of calcium intracellualryl
0
what are the 3 specific needs of the hart
Simultaneous , intermittent contraction of all fibres - pump out of ventricles
Prevention of sustained ( tetanic) contraction - fill up to allow second beat
Ability to change rate according to circumstance - ie when you start exercising you can step up the hr - role of calcium
what does a cardiac myocyte AP start at and rise to
-85mV and rises to +20mV - little depolarisation then plateau
the graph looks like a quif
in a cardiac myocte action potential in phase 0 what channels allow inflow of ion
sodium ions enter through fast sodium channels
in initial repolarisation(1) phase what channels open
potassium
sodium close
in phase 2 the plateau occurs why
increased calcium ion permeability
decreased potassium ion permeability
in phase 3 of a cardiac myocyte AP what happens
calcium channels close and slow potassium channels open so K leave and return the cell membrane potential to resting level
Role of calcium in AP - separate from the role of calcium in the SR involved int eh contraction process
Extended duration of AP ensures total ventricular depolarization
where are the pacemaker cells found
The sinoatrial (SA) node or sinus node is the heart’s natural pacemaker. It’s a small mass of specialized cells in the top of the right atrium (upper chamber of the heart). It produces the electrical impulses that cause your heart to beat.
what does a pacemaker cell action potential start at
-60mV
which ap has no resting phase
pacemaker cell action potential
Starts at -60mV with slower upward trajectory
Sodium inflow is slow and with end calcium inflow
When it hits -40mV hits a higher and quicker depolarization
Repolarization is with potassium otuflow
true or false
true
when the sympathetic system affect HR what happens
slow sodium channel permeability increases
and the slope of phase 4 so depolarisation becomes stepper so threshold is reached sooner therefore incresing the HR
when the parasympathetic system affects HR what happens
increases the resting potassium permeability
trough potential is then lowered and the phase 4 slope becomes flatter so threshold is reached later therefore decreasing the HR
does the AV node slow conduction by 100ms? what does this time allow and prevent
allows time for atrial emptying and protects the ventricles from atrial tachyarrhythmias
His-purkinje system → ventricles - depolarize from in to out ( opposite of perfusion)
Myometirum - interconnected webbing so can spread the signal
Branching nature of cardiac muscle alos enables synchronous ventricular contraction
on an ECG describe the polarity of impulses
Positive if towards recording electrode
Negative if away from recording electrode
negative to positive is depolarisation
which leads should be the strongest
V2
most postive signal
when
the main electrical flow is away from the aVR so produce what kind of signal
negative signal
so ECG thing upside down
main electrical impulses are towards what electrode giving a positive signal
lead II
the main electrical flow is at 90 degrees t o this lead so signal is largely neutral
lead III - so small like one bump in the ECG
what leads are lateral
I
aVL
V5
V6
what leads are inferior
II
III
AvF
AvR - recriporcla view
what leads are anterior
V3,4
count big squares between QRS complex determines what and divide that into 300
HR
