Autonomic dysreflexia is caused by loss of connection from the brain to which neurons leading to unstable blood pressure?

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

Answer: (A)

Autonomic dysreflexia happens when brain control over the spinal autonomic pathways is lost, so the body below the injury experiences unopposed sympathetic activity. After a high-level spinal cord injury, noxious or visceral stimuli below the injury send signals upward but can’t reach higher centers to modulate the response. The result is unchecked activation of sympathetic preganglionic neurons in the spinal cord, causing widespread vasoconstriction below the level of injury and a dangerous rise in blood pressure. In response, the body may activate parasympathetic signals above the injury to attempt to compensate, but these cannot reverse the vasoconstriction below the injury because the connection from brain to those sympathetic neurons is severed. Hence, the sympathetic preganglionic neurons are the key players. The other options don’t fit because parasympathetic postganglionic neurons mediate different, above-injury effects; motor neurons control skeletal muscle; and sensory neurons relay information rather than produce the autonomic vascular response.