Lecture 9- Electrical And Molecular Mechanisms Flashcards
What determines RMP?
Potassium permeability
What creates the potassium equilibrium potential?
The chemical potential pushing K+ out of the cell and the electrical potential pushing K+ into the cell.
What is required to cause contraction?
A rise in calcium
What’s the difference between the action potentials of the heart and that of axons and skeletal muscles?
They are a lot longer in the heart
Describe the ventricular action potential?
Voltage gated Sodium channels open initially. This causes depolarisation. At a certain point K+ channels open transiently and potassium flows out to depolarise slightly. Then calcium channels open and then K+ channels open again to depolarise
SA node action potential?
Funny current due to sodium influx causes slow depolarisation until a certain point is reached. At this point calcium channels open and depolarisation happens quickly. Then voltage gated potassium channels open and depolarisation occurs. Funny current activates at potential below -50 mv.
Why does the SA node set the heart rate?
It depolarises the fastest although the AV node and cells of the ventricles can take over if needed
What is the term used if no action potentials are generated at all?
Asystole
What causes fibrillation?
Electrical activity becomes random
Hyperkalaemia effect?
Higher potassium concentration outside cell so more moves in. Leads to easier a RMP closer to threshold. Can cause increased excitability at first as easier to depolarise. Later can cause asystole. Means that less voltage gated potassium channels will open if RMP is closer to threshold. This means that action potential depolarisation will be slower and conduction will be slower
Effect of hypokalaemia?
Lengthens AP aand delays depolarisation due to less K+ being present outside the cell.
Can cause early after depolarisations before cell has completely repolarised and this results in ventricular fibrillation
Excitation contraction coupling in cardiac cells?
Action potential travels down T tubule and across cell causing calcium influx. Calcium influx causes calcium release from the sarcoplasmic endoplasmic reticulum through the ryanodine receptor. Calcium then causes contraction
How does excitation contraction coupling in smooth muscle occur?
Depolarisation results in VGCCs opening and Ca2+ entering the cell . Noradrenaline acting at alpha 1 receptors will also cause calcium to enter through the SR. Calcium binds camodulin which binds myosin light chain kinase. This phosphorylates myosin head and activates it. Myosin light chain phosphorylase removes the phosphate and inactivates it unless it is inhibited by PKC.
Myosin light chain kinase can be inhibited by PKA
