<prompt> TRUE regarding human heaConduction of impulse from endocardium to inwardsDuring exercise duration of systole is reduced more than diastoleHR increases with parasympathetic denervationVagal stimulation decreases force of contraction  <response>: C i.e. Hea rate increases with parasympathetic denervationThe duration of systole is much more fixed than that of diastole and when the hea rate is increased eg. in exercise, diastole is shoened to a much greater degree.QSympathetic parasympathetic innervationVagal parasympathetic fibres are mainly distributed to atria not much to ventricles. This explains the fact that the main effect of vagal stimulation is to decrease hea rate rather than to decrease the strength of hea contraction greatly which is dependent on ventricleSympathetic noradrenergic fibres are distributed to both atria ventricle. So its stimulation has a strong effect on both hea rate chronotropic force of contractionionotropicFeatureSympatheticadrenergicstimulationParasympatheticcholinergicstimulationHea ratechronotropicIncreasedDecreased mainConductionIncreasedDecreasedForce ofcontractionlonotropicIncreasedDecreased to alesser extentDenervation- At rest, there is a moderate amount of tonic discharge in cardiac sympathetic nerves, whereas vagal tone tonic discharge is of good amount.- So when vagi are cut or parasympatholytic drug eg atropine is given the normal resting hea rate rises from 70 to 150-180 beatsmin due to unopposed sympathetic tone. Q- If both noradrenergic cholinergic systems are blocked, the hea rate is -100 beats min. 