Lecture 9 - Electrical and Molecular Events

Question 1

Define the 4 terms from this lecture that describe abnormal states of the heart

Answer 1

Bradycardia - a slow heart rate / slower AP (a sinus bradycardia if SA node fires too slowly)

Tachycardia - fast heart rate / Fast AP (a sinus
Tachycardia if SA node fires too quickly)

asystolic - No heart beat / no AP

fibrilation - Random / irregular heart beat

Question 2

draw the action potentials with values for

1. Cardiac myocytes
2. the SA Node

label the flow of ions at each stage through specific channels

Answer 2

check in lecture

the SA node funny current is called the pacemaker potential - know this - HCN is activated at -50mv

Question 3

what are conditions relating to the heart and K+ conc ?
what values do they occur at ?

outline the effects of these conditions

Answer 3

normal K+ conc - 3.5 - 5.5 mmol/L-1

Hypokalemia - below 3.5
lengthens AP, delays repolarisation - causes
Early After Depolarisations - EAD’s
Ventricular Fibrilation

Hyperkalemia - above 5.5

Depolarises the potential
some Na+ channels inactivated due to this
slope of depolarisaiton is therefore slower
get a slower and shorter AP, slower and shorter contraction

this can cause asystole, after a period of excitability, tray with calcium gluconate

Question 4

outline the system of contraction in the blood vessels

draw this and label it

Answer 4

key things to remember

vessels contain smooth muscle

myosin light chain kinase - MLCK
myosin light chain phosphotase - MLCP

we can phosphorylate MLCK via PKA to deactivate contraction

PKC inhibits MCLP - this stops inactivation and hence is what gives smooth muscle cells their prolonged contractions

Question 5

what is the length of a cardiac AP

Answer 5

280 ms - this is longer than normal - due to the plateu of Ca2+ channels and K+ efflux balancing