Vagal stimulation of the heart causes

(B) (Increased R-R interval in ECG) (113-Gugton 11th)* Vagus is the parasympathetic supply to the heart its stimulation causes- Decreased heart rate- Decreased force of heart contraction- Decreased cardiac output* R-R Interval is the time interval between consecutive heart beat in the electrocardiogram.So a decrease in heart rate increase the R-R interval* Reverse affects on the heart are noted due to sympathetic stimulation (Noradranaline)* During exercise the diastole is shortened more than systole **Control of Heart by the sympathetic (Noradrenaline) and parasympathetic (vagus) nervesParameterParasympathetic (ACH) StimulationSympathetic (ADR)StimulationForce of cardiac contraction (inotropic effect)Decreased (mainly atria little effect on ventricle)IncreasedConductivityDecreasedEnhancedRate of cardiac contractionDecreased (Bradycardia)Increased (Tachycardia)Vagal (parasympathetic) fibers arc distributed mainly to the atria and not much to the ventricles. Thus the major effect of vagal stimulation is to decreased the heart rate or rate of cardiac contraction (bradycardia) Negative inotropic effect of vagal stimulation is less pronouncedSympathetic fibres are distributed to both the atria and the ventricles. Thus sympathetic stimulation has a strong effect on both the heart rate and the force of cardiac contraction* Complete denervation of heart rate will cause an increase in the resting heart rate.Effect of Denervation of the heart (Ganong; Chaudhuri)* The normal heart rate at rest in young persons is about 70/minute (Range between 50-100/min)* The sinuatrial node (SAN) is the normal pacemaker of the heart and generates a rhythm of about 100/minute* The normal heart rate of about 70.min in a young adult is maintained as a result of autonomic influences on the SAM* When both vagal & sympathetic nerves are removed (denervated heart), the sinuatrial node becomes free from all autonomic (sympathetic & parasympathetic) influences and starts generating its normal rhythm of about 100/min* As the normal resting heart rate is usually less, about 70/min, complete denervation of the heart would cause an increases in the heart rate from 70/min to 100/minNodeIntrinsic Rhythm citySinuatrial node (SAN)Atrio ventricular nodeHis - purkinje system100/min50/min30-40/minDuring exercise the diastole is shortened more then svstole.Changes in Duration of systole and Diastole, when heart rate is increased (Exercise)* Exercise is associated with an increase in the heart rate.* Cardiac muscle has the unique property of contracting and repolarizing faster when the heart rate is high* This leads to a decrease in duration of both systole and diastole'"However the duration of systole is much more fixed than that of diastolic and when the heart rate is increased (eg. Exercise) diastole is shortened to a much greater degree" - Ganong* This longer duration of diastole enables;Superior coronary blood flow to the cardiac musculature Q superior ventricular filling Q