ECGs

Question 1

what triggers the heart beat

Answer 1

depolarisation via an action potential from the sa node

Question 2

what is the sa node

Answer 2

autorhythmic cells that initiate action potentials, no resting potential slowly drifts to threshold

Question 3

how does the sa node trigger an action potential

Answer 3

1. 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

Question 4

what are cardiomyocytes

Answer 4

contractile cells that carry action potentials but cannot generate their own -90mv resting

Question 5

how do cardiomyocytes transmit an action potential

Answer 5

1. sodium influx = rapid depolarisation, potassium channels open 2. plateau - calcium opens - contraction3. rapid repolarisation by delayed rectifier potassium channels 4. resting potential

Question 6

what is excitation-contraction coupling

Answer 6

1. 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

Question 7

how do extracellular potassium levels affect resting potentials

Answer 7

high = depolarisation and inactivated channels - arrythmias low = hyperpolarisation - bradycardia

Question 8

how does calcium homeostasis affect membrane permeability

Answer 8

high calcium = cardiac rhythm abnormalities

Question 9

how do calcium channel blockers work

Answer 9

reduce contraction force

Question 10

how does digoxin work

Answer 10

increases cytosolic calcium and contractility

Question 11

what do ECGs do

Answer 11

assesses electrical activity of heart

Question 12

what is the p wave

Answer 12

depolarisation of atrium in response to SA

Question 13

what is the PR segment

Answer 13

delay of av node allowing access to ventricles

Question 14

what is the QRS complex

Answer 14

ventricular depolarisation

Question 15

what is the ST segment

Answer 15

ventricular repolarisation

Question 16

how do beta blockers affect pacemaker cells

Answer 16

slows funny channels - slows heart rate (class 2 VW)

Question 17

how do sodium channel blockers affect cardiomyocytes

Answer 17

slows depolarisation

Question 18

how do calcium channel blockers affect cardiomyocytes

Answer 18

shorten the plateau

Question 19

how do potassium channel blockers affect cardiomyocytes

Answer 19

extend action potential

Question 20

how do beta blockers affect cardiomyocytes

Answer 20

extend resting potential