Lecture 21

Question 1

Describe the numbers involved with a cardiac action potential

Answer 1

200msec, goes from -90 to +20

Question 2

Describe the shape of the cardiac action potential and the ionic reasoning behind it

Answer 2

0 = rest, K+ lead channels and Na/K ATPase open
1 = rapid upstroke/depolarization = Na open
2= notch = Na close, fast K channels open
3= plateau = K channels close, Ca channels open
4 = repolarization = Ca channels close, slow K channels open
all channels open at the same time (moment of depolarization) but kinetics of opening at different rate
has 2 refractory periods (relative and absolute)
much longer than other AP to prevent tetanus (approximately same length of time as the muscle twitch)

Question 3

Describe the pacemaker AP

Answer 3

Funny channels (If) (HCN = hyperpolarization-activated cyclic nucleotide gated channels) are open to both Na and K, net depolarization leads to rhythmic action potentials driven by Ca channels

Question 4

Describe EC coupling in cardiac muscles

Answer 4

AP enters from adjacent cell, voltage gated Ca channels open, allows Ca to enter, CICR from RyR at the SR, causes calcium spark that sums into calcium signal (mainly from SR), Ca binds to troponin to initiate contraction
Relaxation through SERCA and NCX

Question 5

Describe the ideal ECG

Answer 5

P wave = atrial depolarization
QRS complex = atrial repolarization and ventricular depolarization
T wave = ventricular repolarization
PR interval = atrial contraction
ST segment = ventricular contraction

Question 6

Describe common arrhythmias

Answer 6

tachycardia = too fast
bradycardia = too slow
fibrillation = not contracting in unison
atrial = hear still functions, ventricular = fatal