12.5.1 Maintaining the Human Heartbeat

Question 1

Maintaining the Human Heartbeat

Answer 1

• The human heartbeat is controlled by the following sequence of events: 1. impulse arrival at the sinoatrial node; 2. spread of depolarization across the atria and to the atrioventricular node; 3. contraction of the atria; 4. impulse delay; 5. movement of the impulse towards the apex of the heart and contraction of ventricular muscle.
• There is a theoretical maximum of 240 beats per minute possible in the human heart. The practical maximum is about 180 beats per minute.
• The ECG allows a cardiologist to diagnose various heart abnormalities.

Question 2

sinoatrial node

Answer 2

• Cells at the sinoatrial node maintain the heart’s beating rhythm by self-exciting at regular intervals.

Question 3

atria

Answer 3

• The sinoatrial node excites and an electrical impulse causes contraction of both atria. Once the signal reaches the atrioventricular node, there is a delay. During this time, blood in the atria flows into the ventricles.

Question 4

apex

Answer 4

• The electrical signal then travels from the atrioventricular node towards the apex of the heart. The signal travels through the Purkinje fibersresulting in a contraction of the ventricles

Question 5

electrokardiogram

Answer 5

• An electrokardiogram is used to record the electrical activity of the heartbeat. In the EKG to the left, the first small peak, P, represents atrial depolarization, which is triggered by the self-excitation of the sinoatrial node.
• Portions QRS represent the depolarization of the ventricle and its associated contraction. The ventrical nerves must then repolarize, shown as portion T in the EKG

Question 6

What is the purpose of the 0.1 second delay at the atrioventricular node?

Answer 6

• The delay allows the blood in the atria to empty into the ventricles.

Question 7

Which of the following statements regarding the human heartbeat is true?

Answer 7

• Both atria simultaneously contract.

Question 8

Cells of the heart’s _______________ maintain the beating rhythm by self-exciting at regular intervals.

Answer 8

• sinoatrial node

Question 9

True or false?

There is a 0.1 millisecond delay at the atrioventricular node.

Answer 9

• false

Question 10

One heartbeat is about _______________ long.

Answer 10

• 0.25 seconds

Question 11

What is the observable, or practical, maximum rate of the heart?

Answer 11

• 180 beats per minute