**Core Concept**
Neurogenic shock is a type of shock characterized by vasodilation, bradycardia, and hypotension due to loss of sympathetic tone in the vasculature, often resulting from severe spinal cord injury or high cervical spinal cord lesions.

**Why the Correct Answer is Right**
In neurogenic shock, the sympathetic nervous system's ability to maintain vascular tone is compromised, leading to unopposed parasympathetic activity and subsequent vasodilation. This results in a decrease in systemic vascular resistance (SVR), causing a drop in blood pressure. The body attempts to compensate for this by increasing heart rate, but the resultant bradycardia is a hallmark of neurogenic shock. The loss of sympathetic tone also impairs the body's ability to maintain peripheral vascular resistance, leading to a decrease in blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because neurogenic shock is not primarily characterized by a decrease in cardiac output or a failure of the heart to pump effectively.

**Option B:** This is incorrect because neurogenic shock does not involve an increase in systemic vascular resistance or a constriction of blood vessels.

**Option C:** This is incorrect because neurogenic shock is not primarily caused by anaphylaxis or an allergic reaction.

**Clinical Pearl / High-Yield Fact**
A key feature of neurogenic shock is the presence of bradycardia, which is often a distinguishing feature from other types of shock. A heart rate of less than 60 beats per minute in a patient with suspected spinal cord injury should raise suspicion for neurogenic shock.

**Correct Answer: A. Decreased systemic vascular resistance, bradycardia, and hypotension.**