Which ONE of the following statements about the conduction system of the heart i

Question

Which ONE of the following statements about the conduction system of the heart is INCORRECT? Select one: Electrical events can spread directly between atria and ventricles through gap junctions. The Bundle of His receives impulses from the atrioventricular node. The sinoatrial node is the normal pacemaker of the heart. Purkinje fibres have the fastest rate of conduction of all parts of the conducting system. The atrioventricular node has a slower inherent rate of discharge than the sinoatrial node. Which ONE of the following statements about an action potential generated from a non-pacemaker cardiac cell is INCORRECT? Select one: Depolarisation is initiated by rapid entry of Na^+. The refractory period in ventricular muscle corresponds approximately to the plateau phase of the action potential. Repolarisation occurs as a result of inactivation of K^+ channels. The plateau phase of the action potential is associated with a prolonged increase in Ca^2+ permeability. The resting membrane potential depends to a great extent on the permeability of the cell membrane to K^+. Which ONE of the following parameters, when increased, will cause an increase in cardiac stroke volume? Select one: end-diastolic volume (EDV) after load blood pressure peripheral resistance end-systolic volume (ESV) Closure of the aortic valve is associated with all of the following except: Select one: relaxation of the ventricle. Rapid filling of the left ventricle. The second heart sound. Dicrotic notch on the aortic pressure wave. T- wave of the ECG.

Explanation / Answer

1. Electrical events can spread directly between atria and ventricles through gap junctions. [They must pass through the AV node. The atria are insulated from the ventricles by the atrioventricular groove.]

2. Repolarisation occurs as a result of inactivation of K+ channels. [Repolarisation occurs as a result of activation of K+ channels. ]

3. end-diastolic volume (EDV) [Stroke volume = end-diastolic volume - end systolic volume. So if end-diastolic volume is increased, stroke volume would increase.]

4.rapid filling of the left ventricle. [Closure of the aortic valve is not associated with rapid filling of the left ventricle. Rapid filling of the left ventricle occurs some time after the aortic valve has closed. ]

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