Celullar And Molecular Events In The CVS Flashcards
Why does the K+ gradient maintain the resting potential?
K+ ions move out of the cell down the concentration gradient, and this movement of ions makes the inside of the cell negative with respect to outside.
In cardiac cells, why is the RMP not exactly equal to Ek?
Ek= -95 mV, resting membrane potential= -90mV, due to small amount of permeability to other ions.
How is a cardiac action potential generated?
Upstroke due to the opening of the voltage gated Na+ channels, intiation repolarisation due to rise in outward K+ generation, plateau due to the opening of voltage gated Ca2+ channels, reploratisiatin due to the efflux of K+ through the voltage gated K+ channels.
How is exciation and contraction coupled in cardiac myocytes?
Action potential triggers a rise in the cytocoli ca2+, which is required so that actin and myosin can interact.
What is the pacemaker potential?
This is the gradual depolarisation in the SA node, which reaches a threshold to generate a action potential.
How is the pacemaker potential generated?
HCN channels, (Hyper polarisation activated cyclic nuceltodie gated channels), allow the influx of Na+ that depolarises the cell.
How do the structures of cardiac myocytes facilitate electrical conduction?
Gap Junctions permit movement and allow the electrical coupling of cells. And the cells are joined at the intercalated discs
How is cytosolic calcium increased by an action potential?
Depolarisation opens L type Ca2+ calcium reales channels in the t tubule system, and localised calcium entry opens the calcium induced calcium channels in the sacroplasmic reticulum.
How does calcium cause cardiac muscle contraction?
Ca2+ binds to troponin c, and the confirmational change shifts tropomysoisn to released the ysoin binding site of the actin.
How is (Ca2+) returned to resting levels?
Some exits across the cell membrane, in the sacrolemal Ca2+ATPase, and the Na+/Ca2+ exchanger. Most goes into the sacroplasmic reticul using the SERCA pump that is stiumlated by raised (ca2+) levels.
How does noradrenaline increase the amount of Ca2+ that is realeased into smooth muscle?
The noradrenaline activates the a2 receptors, causing the release of IP3 and release of calcium form the sacroplasmic reticulum
How does Ca2+ cause the contraction of smooth muscle?
Ca2+ binds to calmodulin, which activates the myosin light chain kinase, which phosphorylates the myosin light chain to permit interaction with actin.
How does smooth muscle relax?
Relaxtion occurs as Ca2+ levels decline, and Myson Light chain phosphoyles switches the myosin light chains off.
How is the resting membrane potential maintained in cardiovascular tissue?
At rest, most K+ channels are open making the cell very permeable to K+ ions. (Not the Na=/K+ pump, which just sets the gradients)
