electrical properties of the heart Flashcards
What is excitation-contraction coupling?
the conversion of an electrical signal into a physical contraction
What is the main difference between skeletal muscle cells and cardiac muscle?
skeletal muscle cells = syncytium
cardiac muscle cells = functional syncytium, as they are not actually fused together but are very tightly bound so that when one cell becomes excited, AP is passed on very quickly through the interconnections
describe how the electrical signal is passed on from cell to cell in cardiac cells
through structures within intercalated discs called gap junctions
what is the difference between a cardiac muscle AP & and a skeletal muscle AP & why
cardiac muscle AP is much longer because;
- calcium comes from outside the cell
- calcium dependant calcium release occurs when calcium enters during the AP
- the force of contraction is dependant on calcium entering aka if less calcium, weaker contraction
can cardiac muscle display tetanus?
no, as it requires a long refractory period. The cardiac cell needs to relax before it can contract again. If a heart displays titanic contraction, you will die
what are the two types of cardiac muscle cells?
pacemaker & non-pacemaker
what is a feature of pacemaker cells & give 3 examples of them
non-stable RMP - around -60mv
SA node
AV node
Bundle of His/Purkinje fibres
what is the process of how an AP triggers CDCR
AP travels along sarcolemma and depolarises cell membrane
this activates voltage gated calcium channels (L-type) and triggers influx of calcium, which then triggers more calcium to be released into cytosol (calcium dependent calcium release)
explain the process of depolarisation & repolarisation in non-pacemaker cells
phase 0- stable resting membrane potential - around -90mv - high permeability to K+ channels
phase 1- rapid depolarisation - influx of Na
phase 2- slow repolarisation (plateau) - influx of Ca+
efflux of K+
phase 3- rapid repolarisation- Ca+ channels shut, efflux of K+ only
describe the process of depolarisation & repolarisation in pacemaker cells
repolarisation- Ca channels closed, K channels open, K+ efflux
slow depolarisation- Na+ channels open
rapid depolarisation- Na+ channels close, Ca channels open
give 7 modulators of electrical activity
- drugs
- temperature
- parasympathetic & sympathetic system
- hyperkalaemia
- hypokalaemia
- hypercalcaemia
- hypocalcaemia
give 2 examples of drugs which can modulate electrical activity of the heart
cardiac glycosides - increase force of contraction e.g. Digoxin
Ca+ channel blockers - fewer cross bridges form so decreased strength of contraction
how does temperature affect electrical activity of the heart
increase in 10bpm for every degree above 37degrees celsius
what is hyperkalaemia, how does it affect the heart, and why
high plasma potassium. May lead to fibrillation and heart block. This is because, since there is high extracellular potassium, the concentration gradient decreases and RMP decreases. If RMP decreases, so too do the number of sodium channels and hence sodium influx decreases. Membrane depolarisation takes longer and therefore conduction is delayed
what is hypokalaemia and what effect does it have on the heart
low plasma potassium. Fibrillation and heart block
