The normal pacemaker of the heart is the:
Purkinje fibers.
AV bundle.
Sinoatrial node.
Atrioventricular node.
The Correct Answer is C
The sinoatrial (SA) node is the natural pacemaker of the heart.
It generates electrical impulses that cause the heart’s chambers to contract, setting the heart rate.
The SA node typically generates 60–100 heartbeats per minute when a person is at rest.
Choice A is wrong because Purkinje fibers are part of the electrical conduction system of the heart that carries impulses to the ventricles.
They are not the primary source of impulses.
Choice B is wrong because the AV bundle (also called bundle of His) is another part of the electrical conduction system of the heart that connects the atria and the ventricles.
It is not the natural pacemaker of the heart.
Choice D is wrong because an atrioventricular node is a relay station between the atria and the ventricles that delays the electrical impulses from the SA node.
It can act as a backup pacemaker if the SA node fails, but it is not the normal pacemaker of the heart.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
This means that the electrical activity that causes the atria to contract starts from the sinoatrial node and spreads across the atria.
The P wave on the ECG reflects this atrial depolarization.
Choice A is wrong because repolarization of atrial muscle fibers is not visible on the ECG, as it occurs during the QRS complex when the ventricular depolarization masks it.
Choice C is wrong because the depolarization of ventricular muscle fibers is represented by the QRS complex on the ECG, not the P wave.
Choice D is wrong because the repolarization of ventricular muscle fibers is represented by the T wave on the ECG, not the P wave.
Normal ranges for the P wave are:
Duration: less than 0.12 seconds (less than 3 small squares)
Amplitude: less than 2.5 mm (0.25 mV) in the limb leads, less than 1.5 mm (0.15 mV) in the precordial leads
Axis: between 0° and +75°12
Correct Answer is B
Explanation
Epinephrine, also known as adrenaline, is a hormone that the adrenal medulla secretes in response to stress or low blood sugar levels.
It helps the body react to stress by increasing blood pressure, heart rate, oxygen delivery to muscles, and blood sugar levels.
Choice A is wrong because mineralocorticoids are hormones that the adrenal cortex secretes, not the adrenal medulla.
They help regulate the balance of sodium and potassium in the body.
Choice C is wrong because glucocorticoids are also hormones that the adrenal cortex secretes, not the adrenal medulla.
They help control the body’s use of fats, proteins, and carbohydrates, suppress inflammation, and regulate blood pressure and blood sugar.
Choice D is wrong because aldosterone is a specific type of mineralocorticoid that the adrenal cortex secretes, not the adrenal medulla.
It helps regulate the balance of sodium and water in the body.
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