Video Transcript
The flowchart provided outlines the
basic process of electrical activity that generates a heartbeat. What word would correctly replace
the blank in statement 4?
Our hearts are vital organs. They pump blood throughout the
body, beating 70 times a minute on average. The electrical signals that
regulate the heartbeat are said to be myogenic because they are generated in the
cardiac muscle of the heart. These signals manifest in a
predictable pattern of muscle contraction and relaxation called the cardiac
cycle.
This diagram shows us a
representation of the front of the heart, like we would see it when we would look at
the heart of a person opposite us. When we look at the heart in this
way, the heart’s right side is on your left and vice versa. We need to recall some important
terminology before we try to answer the question. To do that, let’s begin by looking
at the four chambers of the heart. The right atrium is located on the
top left of the heart from our perspective, and the left atrium is on the top right
of this diagram. Below each appropriate atria are
the left and right ventricles.
Next, let’s discuss the blood flow
through the blood vessels in the heart. The vena cava brings blood coming
from the body toward the right atrium. When the atrium contracts, the
blood flows into the right ventricle. During ventricular contraction, the
blood is pushed into the pulmonary artery, which delivers the blood from the heart
to the lungs, where it takes up oxygen. The pulmonary vein transports
oxygenated blood from the lungs to the left atrium of the heart. When the left atrium contracts, the
blood flows into the left ventricle. The ventricle then contracts,
pushing blood into the aorta, which leads oxygenated blood away from the heart to
the body cells.
Now that we understand the main
parts of the heart and the blood flow through it, let’s go over the cardiac cycle to
understand how the bioelectricity, which is responsible for contraction and
relaxation, is generated. The cardiac cycle starts when the
atria fill with blood. First, electricity is generated as
an impulse in the sinoatrial node, or SAN, which is found in the wall of the right
atrium, as described in statement 1 in the flowchart. The impulse travels through the
atria, causing them to contract, as described in statement 2 in the flowchart. This pushes blood from the atria
into the ventricles. The impulse then reaches the
atrioventricular node, or AVN, which is found between the right ventricle and the
right atrium.
The impulse is further transmitted
to the bundle of His, in the center of the heart, as is described in statement 3 in
the flowchart. This causes a slight delay, so the
ventricles have time to fill with blood. The bundle of His helps the
electrical impulse travel down and into the Purkinje fibers, as described in
statement 4 in the flowchart. The Purkinje fibers are found in
the walls of the ventricles. The impulse travels up the Purkinje
fibers, which causes the ventricles to contract, as described in statement 5, and
push blood through the arteries.
Now that we understand the cardiac
cycle, we can answer the original question as we know which word should replace the
blank in statement 4. The impulse passes from the bundle
of His to the Purkinje fibers, which are in the walls of the ventricles.
