What is the ability of cardiac cells to respond to an impulse by contracting?

Correct Answer: A

Rationale: The correct answer is A: Excitability. Excitability refers to the ability of cardiac cells to respond to an impulse by generating an action potential and contracting. This is the fundamental property that allows the heart to beat. Contractility (B) is the ability of cardiac muscle to contract once stimulated, but it does not specifically refer to the response to an impulse. Rhythmicity (C) is the ability of cardiac cells to generate spontaneous electrical impulses, not directly related to responding to an impulse. Conductivity (D) is the ability of cardiac cells to transmit electrical impulses, not specifically related to the response of cells contracting.

Correct Answer: A

Rationale: The correct answer is A: Carotid body. The carotid body is the major chemoreceptor of the heart, detecting changes in oxygen levels in the blood. It sends signals via the glossopharyngeal nerve to regulate heart rate and blood pressure. The aortic body primarily monitors blood pressure, not chemoreception. The vagus nerve plays a role in regulating heart rate but is not a chemoreceptor. The SA node is the pacemaker of the heart, responsible for initiating the electrical signals for heart contraction, not chemoreception. Therefore, the carotid body is the correct choice for the major chemoreceptor of the heart.

Correct Answer: A

Rationale: Automaticity is the ability of cardiac cells to generate an electrical impulse spontaneously without external stimulation. It is a fundamental property of specialized cardiac cells like pacemaker cells. Contractility refers to the ability of muscle cells to contract in response to an electrical stimulus. Conductivity is the ability of cardiac cells to transmit electrical impulses. Refractoriness is the period during which cardiac cells are unable to respond to a new stimulus. Therefore, in this context, the correct answer is A: Automaticity.

Correct Answer: A

Rationale: The correct answer is A: Purkinje fibers. Purkinje fibers are specialized cardiac muscle fibers that distribute the electrical impulse from the AV node to the ventricles, causing them to contract. They are located in the ventricles and ensure synchronized and efficient contraction. The SA node (B) is the pacemaker of the heart, initiating the electrical impulse. The AV node (C) delays the impulse to allow for atrial contraction before ventricular contraction. The Bundle of His (D) is a pathway for the electrical impulse from the AV node to the bundle branches, which then lead to the Purkinje fibers for ventricular contraction.

Correct Answer: A

Rationale: The correct answer is A: Angina. Angina is characterized by chest pain due to reduced blood flow to the heart muscle, often triggered by physical exertion or stress. It is typically relieved by rest or medication. Myocardial infarction (B) is a heart attack, which results from a complete blockage of blood flow to a part of the heart muscle. Pericarditis (C) is inflammation of the pericardium, the outer lining of the heart, causing sharp chest pain that worsens with breathing. Arrhythmia (D) refers to abnormal heart rhythms and may not necessarily present with chest pain due to reduced blood flow.