SA node acts as a pacemaker of the heart because of the fact that it:

Correct Answer: D

Rationale: The SA node (D) fires fastest (~60-100 bpm), outpacing others. A is true but general, B and C are partial (it has both innervations).

Correct Answer: D

Rationale: The vagus nerve (D) (parasympathetic) slows heart rate via acetylcholine. Cardiac accelerator (A) (sympathetic) increases it, hypoglossal (B) and spinal accessory (C) are unrelated.

Correct Answer: C

Rationale: Anxiety and fear (C) increase heart rate via sympathetic activation. Pain (A) and cold (B) may slow it via vagal reflexes, grief (D) varies.

Correct Answer: B

Rationale: The ventricles (B) are the lower, pumping chambers. Atria (A) receive, auricles (C) extend atria, coronary sinuses (D) are veins.

Correct Answer: B

Rationale: Systolic pressure (B) is the pressure during ventricular contraction (~120 mmHg). Diastolic (A) is relaxation, pulse (C) is the difference, mean (D) is average.