Autonomic dysreflexia is caused by loss of connection from the brain to which neurons?

• A. Sympathetic preganglionic neurons
• B. Parasympathetic postganglionic neurons
• C. Motor neurons
• D. Sensory neurons

Answer: (A)

Autonomic dysreflexia happens when the brain can no longer modulate the sympathetic nervous system below a high spinal cord injury. Descending pathways from the brain normally dampen the activity of sympathetic preganglionic neurons in the spinal cord. When the connection is lost, a noxious or even minor stimulus below the injury triggers an unrestrained sympathetic discharge, causing vasoconstriction and a dangerous rise in blood pressure. The unregulated activity is centered on the sympathetic preganglionic neurons, which is why that option is correct. The other options don’t fit because dysreflexia is driven by uncontrolled sympathetic outflow, not by parasympathetic postganglionic neurons, motor neurons, or sensory neurons—the problem is the brain’s loss of control over the sympathetic preganglionic neurons.