4.1 Cellular and Molecular Events in the CVS Flashcards
Describe and explain the shape of a ventricular action potential graph
Steep incline- opening of voltage gated Na+ channels
Small decrease- transient outward K+ current and Na+ channel deactivation
Plateau- opening of voltage gated Ca2+ channels
Steep decline- Ca2+ channels deactivate
What is the purpose of the plateau phase in the ventricular action potential graph?
Allows the whole heart to depolarise and contract at the same time
Describe and explain the shape of the SAN action potential graph
Slow increase- pacemaker potential (funny current) Na+ channels open and inactivate
Steep incline- opening of Ca2+ voltage gated channels
Decline- Opening of voltage gated K+ channels
Which channels allow influx of Na+ ions in the SAN?
Hyperpolarisation-activated cyclic nucleotide-gated channels
HCN channels
Why does the SAN act as the pacemaker in the heart when other areas of the heart can also automatically depolarise?
The SAN depolarises the quickest so sets the rhythm of the heart.
Name 4 features of cardiac muscle
Single, central nucleus
Striated
Branched
Joined at intercalated discs
Describe the process of cell depolarisation to muscle contraction
Ca2+ moves into the cell on depolarisation via L-type channels
CICR channels on the SR are opened by Ca2+ ions
Ca2+ binds to troponin C in an actin filament
The sliding filament theory ensues
How do Ca2+ levels return to normal after contraction?
Pumped back into the SR via SERCA pumps
Some exits via the cell membrane
How is the resting membrane set?
The membrane is permeable to K+
K+ moves OUT of the cell down the concentration gradient but INTO the cell down an electrical gradient.
What controls vascular tone?
The contraction and relaxation of muscles in the tunica media
Explain the process of excitation contraction coupling
Ca2+ binds to calmodulin which activates myosin light chain kinase (MLCK)
This phosphorylates the myosin light chain so it can interact with actin
