heart physiology Flashcards
what is the membrane potential of a cell (Vm)?
potential difference between inside and outside of the cell
what is an action potential?
when tissues excite and cell are stimulated causing a change in potential causing nerve impulse or contraction of muscle
draw diagram of membrane potentials?
slide 3
lecture 8 heart physiology
what is depolarization?
cell becomes more positve
what is repolarization?
returns to negative resting potential
what is hyperpolarization?
more negative than resting potential
what are intercalated discs?
fibres joined end-to-end by specialized functions
what are properties of intercalated discs?
tight interactions
mediate electrical coupling
fibres branch to increase interconnections
one central nucleus
a lot of mitochondria
why are conrtactions synchronized?
to make sure cardiomyocytes work together and that the cardiac muscle works as syncytium
how are gap junctions formed?
by connexin
what is connexin?
integral membrane proteins
what is the purpose of a gap junction?
link cytoplasm to ensure rapid transfer of ions
how does the SA node cause contraction of the heart muscle?
intrinsic waves of excitation spread from SA to node to AV node from right atrium to left atrium via Buchmann’s bundle then to myocytes via bundle of His and purkinje fibres
what is the SA node controlled by?
autonomic system signals
what does the heart muscle consist of?
myocardial and cardiomyocyte fibres
what are the differences between SAN and myocardium?
electrical membrane potentials are different in SAN and myocardium
what happens to pacemaker cells?
If channels open causing depolarization by slow movement of K+ out of cell and faster movement of Na+ into cell occurring and close as threshold potential reached. Some Ca2+ channels open when threshold reached then lots of Ca2+ channels open causing overshoot. Ca2+ channels close and K+ channels open causing repolarization as K+ moves out of the cell and hyperpolarization occurs. K+ channels close and increase in electrical potential causing If channels to open again
draw diagram of action potential of cardiomyocytes?
slide 12
lecture 8 heart physiology
what are the phases in action potential in cardiomyocytes?
Phase 0:Depolarization
action potential triggered causing rise in TMP
Na+ channels open and Na+ enters the cell
threshold reached and rapid depolarization occurs causing overshoot
Na+ channels close and some Ca2+ channels open
Phase 1: early repolarization
TMP slightly positive
Some K+ channels open and K+ leaves cell causing TMP to reach 0 again
Phase 2:Plateau phase
small influx of Ca2+
important in the excitation-contraction coupling process
K+ movement out and down its concentration gradient via delayed rectifier K+ channels
TMP maintained at plateau as its electrically balanced
Phase 3:repolarization
L-type Ca2+ channels close
more K+ ions flow out than Ca2+ flowing in
TMP reaches resting potential
Phase 4:resting phase
outward leak of K+ through inward rectifier channels Na2+ and Ca2+ channels are closed
when is normal transmembrane ionic concentration gradient reached?
when Na+ and Ca2+ are returned to extracellular environment and K+ to the interior
what are the pumps involved in contractile system?
sarcolemmal Na+-Ca2+ exchanger
Ca2+-ATPase
Na+-K+-ATPase
what is the refractory period of cardiomyocytes?
longer than other muscle cells
they have physiological mechanisms that allow for ventricles to empty and refill before next contraction
what are thin filaments composed of?
actin
what are thin filaments composed of?
myosin
