Electrical Activity Flashcards
What is Excitation Contraction Coupling?
The process by which all muscle, skeletal and cardiac contracts
The binding of Actin and Myosin cross bridges modulated by entry of Ca into the cell.
What are intercalated discs?
Alternation of Desmosomes and Gap Junctions, to allow impulses to flow but keep the cells together.
What is a Syncytium?
Multinucleate cell formed when a group of cells merge.
Is the cardiac muscle a syncytium?
It is a FUNCTIONAL syncytium not a true syncytium.
Differences in Cardiac muscle compared to Skeletal Muscle.
1) Longer Action Potential
2) Sub maximal contraction in cardiac muscle
3) Unstable RMP in pacemaker cells
4) No tetanic contraction due to longer refractory period.
What are the benefits of Sub-maximal contraction?
Allows regulation of Ca influx into the cell, force of contraction and therefore Stroke Volume
Pacemaker VS Non-pacemaker
Not two types= a range across the spectrum. From stable to unstable RMP
How do non-pacemaker cells work?
1) Na channels open= rapid depolarisation
2) Slow increase in permeability to Ca and decreased permeability to K= PLATEAU
3) Na shut & K open= REPOLARISATION
How do Pacemaker cells work?
AP= increase in permeability to Ca (l-type) Pre-potential= gradual increase in PK, early increase in PNa, and late increase in Pca (T-type)
What is autorrhymicity?
If you remove the heart it will still beat if in saline- due to random depolarisation of Pacemaker cells.
How does temperature affect Heart Rate?
1 degree increase= 10 BPM
So fever = increased HR
What drugs affect force of contraction?
Ca channel blockers= decrease
Cardiac Glycosides= Increase
Effect of Plasma K+
High= fibrillation and heart block Low= fibrillation and heart block
Effect of Plasma Ca2+
High= increased HR and force of contraction Low= decrease
What is heart block?
When the Action Potentials are travelling so slowly that the action of the AVN stops them completely.
