Ans. B. Atrial refractory periodMost organ receive dual innervation by both SNS and PNS. The level of activity of an organ at a given moment is the sum of sympathetic and parasympathetic tone. However, refractory period of atrial fibers is decreased by sympathetic as well as parasympathetic influences.OrganSNSPNSHeartIncreases HR, ContractionDecreases HRLungBronchodilationBronchoconstrictionGITDecreased motility, Contraction of sphinctersIncreased muscle motilityRelaxation of sphinctersBlood vesselContraction in cutaneous and splanchnic BV, Relaxation in skeletal muscle BVNo direct effect on BV*.Dilation in coronary BV via releases of EDRF(NO)EyeMydriasisMiosis and accommodation for near visionBladderUrinary Retention (contraction of sphincter)Voiding (Contraction of detrusor; relaxation of trigone)GenitaliaEjaculationErection