ECGs Flashcards
what triggers the heart beat
depolarisation via an action potential from the sa node
what is the sa node
autorhythmic cells that initiate action potentials, no resting potential slowly drifts to threshold
how does the sa node trigger an action potential
- funny channels open, slow sodium in 2. transient calcium channels open 3. at threshold funny close, long lasting calcium open 4. peak, long lasting calcium close, potassium opens moves out 5. once repolarised funny opens again
what are cardiomyocytes
contractile cells that carry action potentials but cannot generate their own -90mv resting
how do cardiomyocytes transmit an action potential
- sodium influx = rapid depolarisation, potassium channels open 2. plateau - calcium opens - contraction3. rapid repolarisation by delayed rectifier potassium channels 4. resting potential
what is excitation-contraction coupling
- increase in calcium 2. binds to receptor on sarcoplasmic reticulum - more calcium released 3. calcium and troponin = cross bridge, contraction 4. ryanodine moved Ca back into SR (active) and Na-Ca pump moves Ca out of cell
how do extracellular potassium levels affect resting potentials
high = depolarisation and inactivated channels - arrythmias low = hyperpolarisation - bradycardia
how does calcium homeostasis affect membrane permeability
high calcium = cardiac rhythm abnormalities
how do calcium channel blockers work
reduce contraction force
how does digoxin work
increases cytosolic calcium and contractility
what do ECGs do
assesses electrical activity of heart
what is the p wave
depolarisation of atrium in response to SA
what is the PR segment
delay of av node allowing access to ventricles
what is the QRS complex
ventricular depolarisation
what is the ST segment
ventricular repolarisation
