Q5: The Defecation Reflex: Spinal Cord Injury

A 27-year-old male is brought to the emergency department following a motorcycle accident. Imaging reveals a complete spinal cord injury at the T12 level (lowest vertebra in the thoracic region of the spinal cord). In the days following the injury, the patient reports a lack of bowel movements despite a normal diet. A rectal exam shows a distended rectum with stools present, but the patient does not feel the urge to defecate. 

Given your understanding of the neuronal control of the colon, rectum and sphincters during the defecation reflex, EXPLAIN why this spinal cord injury will lead to constipation and involuntary stool leakage. You must describe the specific types of neurons involved in the ‘normal’ defecation reflex in your answer.

[maximum 250 words]