electrical events in the cardiac cycle

Question 1

action potentials

Answer 1

• resting membrane pot of all cells is electronegative- inside surface -ve with respect to outside)
• excitable cells such as neurons and muscle can undergo rapid cycle changes in membrane potential caused by changes in permeability of the membrane to various ions; called APs
• if the permeability of the membrane to Na+ and Ca2+ increases, this causes depolarisation
• if the permeability of the membrane to K+ increases, this causes repolarisation
• in muscle, APs cause contractions of the cell

Question 2

cardiac myocyte APs

Answer 2

all myocytes are spontaneously active to some degree- atrial and ventricular hardly at all.
the rate of discharge and shape of the AP varied depending on which ions carry the current and channels they use

Question 3

autonomic effect

Answer 3

sympathetic activation- increases slope of pacemaker potential- mediated by increased opening of funny channels, means that the SA node APs arise more frequently
parasympathetic activation both hyperpolarises the SA node cells and decreases the slope of the pacemaker potential. both of these effects are mediated by increased opening of K+ ion channels

Question 4

K+ disturbances and heart rhythms

Answer 4

K+ ion channels and concentrations are very important in determining the ability of cardiac myocytes to repolarise and setting resting membrane potential