Ans. is 'c' i.e., Increased refractory period Sympathetic stimulationPositive chronotropic (Increased heart rate0):- Sympathetic stimulation increases the slope of phase 4 prepotential (pacemaker potential)Q; therefore, time taken to reach the threshold is decreased and heart rate is increased.Positive ionotropic (Increased contractility )Q.in) Positive dromotropic (Increased conduction velocity' in conductive tissueQ).Decreased in refractory period of all ty pe of cardiac cells (Punjab l0).Positive bathmotropic (Increased automaticity).o Pacemaker potential (prepotential) is mainly due to Na+ influx.o Vagal stimulation causes decrease in slop of prepotention (by decreasing Na~ influx).Effects of ANSo The SA node develops from structures on the right side of the embryo and the AV node from structures on the left. This is why right vagus (parasympathetic) is distributed primarily to SA node and the left vagus (parasympathetic) mainly to AV nodeQ. Similarly, the sympathetic innervation on the right side is distributed primarily to the SA node and the sympathetic innervation on the left side primarily to AV node,o Effects of ANS on cardiac physiology are as follow: -Parasy mpathetic (vagal) stimulatio nNegative chronotropic (decreased heart rateQ) : - Vagal stimulation cause decrease in slope (flattening) of prepotential (pacemaker potential) and therefore the time taken to reach the threshold level is increased - Heart rate is decreased.Negative dromotropic (decreased conduction).Increased refractory period of all type of cardiac cells.Sympathetic stimulationPositive chronotropic (Increased heart rateQ):- Sympathetic stimulation increases the slope of phase 4 prepotential (pacemaker potential) Q; therefore, time taken to reach the threshold is decreased and heart rate is increased.Positive ionotropic (Increased contractility ) Q.Positive dromotropic (Increased conduction velocity in conductive tissue6).Decreased in refractory period of all type of cardiac cellsQ.Positive bathmotropic (Increased automaticity).