Answer
Bisecting the spinal cord at the level of C2 causes respiratory arrest because it prevents descending nerve impulses from reaching the phrenic nerve. The diaphragm is the main muscle of breathing, and its contractions are stimulated by impulses carried to it by the phrenic nerve. Consequently, severance of this nerve would mean the cessation of breathing.
Work Step by Step
The phrenic nerve is the most important nerve of respiration. It arises from the anterior rami of the C3 to C5 segements and provides the motor innervation to the central area of the diaphragm. There are two phrenic nerves--one on each side-- but each serves the ipsilateral side of the diaphragm. Damage to one phrenic nerve would result in partial paralysis of the diaphragm with resultant shortness of breath or dyspnea. Mechanical trauma or neuropathies ( as in diabetes) can cause partial diaphragm paraylysis. However, bisecting or severance of the spinal cord at C2 would cut off descending nerve impulses to the diaphragm, the main muscle of breathing. The consequence would be cessation of breathing.
