4. Conduction System Flashcards
What is the difference between depolarisation and hyperpolarisation?
Depolarisation making the membrane potential more positive
Hyperpolarisation making the membrane potential more negative
Define channel, pump and carrier proteins
Channel - protein pore that allows facilitated diffusion of ions
Pump - moves ions against concentration gradient by a conformational change in the membrane spanning protein using ATP
Carrier - proteins that transfer ions or molecules by a conformational change in the membrane spanning protein
Why is there a difference in electrical potential inside vs outside of the cell?
Differences in concentrations of ions inside and outside of the cell
Selectively permeable
What are the two main membrane pumps in the CV system?
Na-K-ATPase
Ca-ATPase
What happens to the electrochemical potential inside of a cell when potassium ions leave?
[also known as the cells resting potential]
Becomes more negative
True/false
The cardiac action potential underlies myocardial function
True
LOOK ON OSMOSIS FOR CARIDAC ACTION POTENTIAL
How are cardiomyocytes electrically linked?
Via gap junctions
What is a syncytium? With regard to the heart
A network of electrically connected cardiac muscle cells
What is connexin 45 Cx45?
A gap junction [pore] linking two cells
What stops cells from firing spontaneous action potentials?
The cells ‘recover’ from the action potentials with refractory periods
Where does the spread of excitation start?
Sinoatrial node
Describe the pathway of the wave of excitation from the SA node
Sa node
Atria
Av node
Purkinje fibres
Ventricular tissue
Describe the process by which spontaneous action potentials that control heart rate are fired.
Unstable baseline that gradually depolarises [slow leak of Na+]
Threshold reached for opening voltage gated T type calcium channels
The further depolarisation causes opening of L type calcium channels
Voltage gated potassium channnels open to restore the membrane potential to a negative level
Process starts again
What is the funny current?
The slow Na+ leak into the cell
What does an ECG measure?
The movement of charge through the myocardium
What is the theoretical membrane potential?
What the membrane potential would be for a membrane that is perfectly selective for a specific ion with known intracellular and extracellular concentrations
What is the equation used for theoretical membrane potential?
Nernst equation
Why is the resting membrane potential never at Ek ?
There is always movement of other ions
The opening of potassium channels leads to _______ of the membrane which causes relaxation of muscle
Hyperpolarisation
Opening channels that pass either calcium or sodium ions causes ________ of the membrane which causes contraction of muscles
Depolarisation
Describe the electrical activity before a heart beat in non pacemaker cells.
Phase 0 - Sodium channels open causing depolarisation
Phase 1- Rapid transient outward current [ITo] of potassium - initial Repolarisation
Phase 2 - ca and k both moving at same time so plateau phase. Long lasting Ca current [sustained depolarisation] from L type calcium channels [Ica]
Phase 3- calcium channels start to close, rapidly activating K+ current [IKr] & slowly activating K+ current [IKs] cause polarisation
Phase 4- inwardly rectifying K+ current IK1
What phase of the cardiac action potential is depolarisation?
0
How long is the phase 2 of the cardiac action potential [long lasting depolarisation]
200-300 milliseconds long
