TRUE regarding human hea
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 ventricle)Sympathetic (noradrenergic) fibres are distributed to both atria & ventricle. So its stimulation has a strong effect on both hea rate (chronotropic) & force of contraction(ionotropic)FeatureSympathetic(adrenergic)stimulationParasympathetic(cholinergic)stimulationHea rate(chronotropic)IncreasedDecreased (main)ConductionIncreasedDecreasedForce ofcontraction(lonotropic)IncreasedDecreased (to alesser extent)Denervation- 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 beats/min due to unopposed sympathetic tone. Q- If both noradrenergic & cholinergic systems are blocked, the hea rate is -100 beats / min.
Conduction of impulse from endocardium to inwards
During exercise duration of systole is reduced more than diastole
HR increases with parasympathetic denervation
Vagal stimulation decreases force of contraction