Neurogenic (vasogenic) shock is caused by which mechanism?

• A. Unopposed parasympathetic response due to loss of sympathetic nervous system innervation
• B. Excess sympathetic stimulation
• C. Hypovolemia
• D. Anaphylaxis

Answer: (A)

Neurogenic (vasogenic) shock occurs when there is a loss of sympathetic tone to the blood vessels, usually from spinal injury that disrupts sympathetic outflow. Without sympathetic signaling, the parasympathetic (vagal) system dominates, causing widespread vasodilation, decreased systemic vascular resistance, and pooling of blood in the venous system. This leads to hypotension. Because the heart is still under vagal influence, the heart rate often slows (bradycardia) rather than speeding up.

This differs from other options: excessive sympathetic stimulation would tighten vessels and raise blood pressure, not produce shock. Hypovolemia causes low blood pressure from reduced blood volume rather than from loss of vascular tone. Anaphylaxis causes vasodilation and capillary leakage due to histamine release, but through allergic mechanisms rather than loss of sympathetic innervation.