Extreme pain causes neurogenic shock by overexciting the parasympathetic nervous system. This results in a significant decrease in heart rate (Bradycardia); which in turn decreases the pulse and leads to a dangerous drop in blood pressure [shock].
The parasympathetic nervous system is involved in decreasing the heart and pulse rate, thus lowering blood pressure.
The signs and symptoms of neurogenic shock are similar to other types of shock, except the heart rate slows down, as well as warm, dry, and flushed skin due to venous pooling secondary to loss of vascular tone. In non-neurogenic types of shock, the heart and pulse speed up. But in the textbooks, neurogenic shock refers to a state where due to spinal cord or CNS injury peripheral release of catecholamines does not occur. This causes loss of vasomotor tone and resultant accumulation of blood in peripheral vessels and shock. This lack of circulation forces muscles to process energy using a form of metabolism called Anaerobic metabolism. A drop in blood pressure must occur as it is a kind of shock. A drop in heart rate will occur, but only if the spinal cord injury involves areas above (Proximal) vertebrae T-6. Below T-6 the heart rate will not be affected, but blood will accumulate in the lower extremities causing warm, dry, and flushed skin. How severe burn or excruciating pain causes neurogenic shock is not clear.
Overexcitation of the parasympathetic nervous system causing neurogenic shock, doesn't relate to conventional textbooks.
Ways neurogenic shock is managed in the medical field is by Vasopressors to help sustain an adequate blood pressure. Examples of Vasopressors are Dopamine, which acts mainly on the Alpha -1 receptors to cause vasoconstriction which in turn raises blood pressure due to less space in the arteries. Dobutamine, which acts on Beta-1 receptors in the body to cause an increase in heart rate. This increase in heart rate raises blood pressure.