Electrical activity of the heart Flashcards
where are the 4 areas of pacemaker cells
SA node
AV bundle
Bundle of His
purkinje fibres
how does the action potential spread from the pacemaker cells into the contractile cells
through gap junctions located at the intercalated disks
what is the resting membrane potential in a cardiac contractile cell
-90mV
what mV is reached when a cardiac cell depolarizes
20mV
what is the function of desmosomes in intercalated disks
they weld the two adjacent cells together
what is the unstable membrane potential of a cardiac auto-rhythmic cell
starts as -60
what gives auto rhythmic cells their ability to generate APs
comes from their unstable membrane potential that starts at -60 and will slowly drift upwards to threshold
what are the channels in auto-rhythmic cells that create the pacemaker potential
If channels
what are If channels leaky for
NA+ and K+
once threshold is reached in an autorhythmic cell what happens next
threshold is reached. IF channels are closed and Ca2+ channels open . Making the cell depolarise further
in autorhythmic cells once the cell has depolarised to 20 mV what channels open
K+ channels open and potassium laves the cell, cell repolarises
what percentage of heart cells are contractile
99%
why does the AV node delay the signal from the SA node
so the atria can finish contracting before the ventricles contract, without this delay all the chambers would squeeze at once and the blood wouldn’t go anywhere.
cardiac muscle has a long refractory period therefore it cannot do what
exhibit tetanic contraction
Ca2+ entry from outside the cell can regulate contraction of cardiac muscle how is this possible
Ca2 release does not saturate the troponin so regulation of Ca2 release can be used to vary the strength of contraction
does the inside or outside of the cell have a higher concentration of K
inside
where is there a higher concentration of Na and Ca, inside or outside the cell
outside
what does the P wave correspond to in an ECG
atrial depolarization
what does the QRS complex correspond to in an ECG
ventricular depolarization
what does the T wave correspond to in an ECG
ventricular repolarisation
in skeletal muscle contraction what does tropinin bind to
Ca2+
what is the purpose of troponin binding to Ca2+ in skeletal muscle
this action causes troponin to pull the tropomyosin away from the actin filament
what binds to the active sites on actin
myosin cross bridge heads
how long is the cardiac action potential
250msec
how long is skeletal muscle action potential
2msec
Ca2+ entry from outside the cell can regulate contraction why is this
as Ca2+ release does not saturate the troponin so entry of more calcium can be used to increase the strngth of contraction
what would Calcium channel blockers do the force of contraction
decrease
what is an example of a cardiac glycocide
digoxin
what do cardiac glycosides do to the force of contraction
increase
what effect does temperature have on the force of contraction
increases it 10 beats/min/ºC
what can too little or too much potassium do to the heart
cause fibrillation and heart block
