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The heart is the main organ of the cardiovascular system. The apex of the heart is part of responsible for regulating ventricle contraction. It is formed mostly by the left ventricle, and it points downward, forward, and slightly to the left.
The heart sits more on the left side of the body than on the right side. To find the apex, one should identify the fifth intercostal space. The numbering of intercostal spaces — the space between two ribs — is done according to the upper rib, so the fifth intercostal space is between the fourth and fifth ribs. The apex is found at this level and around 3 to 3.5 inches (8 to 9 cm) from the sternum.
The function of the apex of the heart is to regulate the contractions of the ventricles so they are well-timed to the contractions of the atrium. This timing is the result of a system of fibers that runs from the top of the atrium to the apex, where the fibers break into two pathways leading to the left and right ventricles. These fibers found within the walls of the heart are known as Purkinje fibers.
The function of Purkinje fibers is to conduct impulses rapidly. They are arranged within the heart and contract to make the heart’s rhythm most efficient. The fibers work together with a few nodes that act to stimulate and regulate the impulses.
The sinoatrial (SA) nodes are areas of the heart's atrium that act as the heart's pacemaker. Impulses from the SA node cause the heart’s chambers to contract. Purkinje fibers receive their impulses from the SA node and move the impulse through the heart’s muscles.
Just below the atrium is another node, the atrioventricular (AV) node, which slows the impulses from the SA node. The slower signal proceeds to the apex of the heart and then around to the left and right ventricles. The timing of the impulses from the SA node to the AV node and on to the ventricles is ideally perfect for the flow of blood from the atrium to the ventricles. Once the blood has reached the ventricles, the Purkinje fibers signal for the ventricle to contract.
The apex functions to cause the ventricles to contract from the bottom up. This provides the driving force that sends the blood up and out of the heart. This efficiency is the result of the combined efforts of the nodes, the Purkinje fibers, and the shape of the heart, particularly the way the apex is formed in the left ventricle.