BIOL 235 Human Physiology EXAM 3 STUDY GUIDE new solution update Athabasca University

CARDIOVASCULAR SYSTEM • Apply the anatomy of the heart to evaluate the control of cardiovascular function. o Heart pumps the blood throughout the circulatory system o Blood vessels ▪ Arteries carry blood away from the heart ▪ Veins return blood to the heart o Ventricles contract from bottom up so that blood is squeezed out of the top o Between the atria and ventricles there are AV valves & between the ventricles and arteries are the semilunar valves (both valves prevent the backward flow of blood) • Compare and contrastthe action potentials generated in skeletal muscle, myocardial autorhythmic cells, and myocardial contractile cells. o Skeletal muscle— ▪ resting membrane potential at -70 mV and graded potential reaches threshold at -55mV, opens vg-Na+ channels, Na+ enters the cell causing depolarization to +30mV ▪ when membrane reaches +30mV, Na+ channels close and K+ channels open ▪ K+ exits the cell causing repolarization ▪ Excessive K+ efflux causes hyperpolarization and leak of Na+ restores membrane potential to resting state. o Myocardial Autorhythmic cells— (there are no vg-Na+ channels) ▪ Pacemaker potential • If channels open allowing Na+ to enter and slowly depolarize the cell along with a reinforced entry of Ca2+ reaching the threshold (-40mV) • If channels close ▪ Rising phase of action potential (rapid depolarization) due to the rapidly opening Ca2+ channels ▪ When membrane reaches peak at +20mV, Ca2+ channels close and K+ channels open. ▪ Repolarization phase due to K+ efflux ▪ When repolarization reaches -60mV, K+ channels close and If channels open again (Na+ enter) slowly depolarizing the cell. ▪ Sidenote: • If vg-Na+ channels blocked, everything would be fine. No vg-Na+ channels • Ca2+ channels here are different than contractile cells; autorhythmic Ca2+ open rapidly o Myocardial Contractile Cells o Resting membrane potential at -90mV o Wave of depolarization movesinto contractile cell, vg-Na channels open, Na+ rushes in rapid depolarization o When membrane potential reaches -20mV the Na+ channels close and K+ channels open. K+ exits the cell and start of repolarization