Nina studies an artificial heart model. The model has tubes that supply an electric current to the model. Nina switches on the current that provides an impulse to the heart. She observes that the heart contracts and relaxes. Compare this model with that of a human heart, and place the steps describing how blood flows through the human heart in order. Tiles

signal transferred to the ventriclesthe atria contractelectrical signal travels toward the heartthe ventricles contractsignal by the nodes in the atriumsignal received by the atrioventricular node

* a mechanical component (rhythmic contractions and relaxations): the cardiac cycle, which is the succession of contraction phases (systole) ejecting the blood out of the left ventricle and relaxation phases (diastole) allowing the filling of the cardiac cavity,

* an electrical component (under fores of electric discharges), directly responsible for the mechanical phase with which it is perfectly synchronized.

The right order is

*Electrical signal travels toward the heart.

*Signal received by the nodes in the atrium

*The atria contract

*Signal received by the atrioventricular node

*Signal transferred to the ventricles

*The ventricles contract

Explanation

* The electric current is born at a specific point of the heart (on the order of a few millimeters in diameter), called sinus node, located at the top of the right atrium.

This consists of cells capable of producing an electric current. Starting from the sinus node, the current propagates in the cardiac muscle (including the two atria) causing their contraction. Then, it converges to the septum of the heart, at the level of an electrical relay called atrioventricular node (NAV).

From the atrioventricular node (NAV), the impulse progresses simultaneously in the 2 ventricles, the right and the left, taking very fast conductive pathways (the Hys beam and the Purkinje network), causing contraction of the ventricles.