Complete transaction of the spinal cord at the C7 level produces all of the following effects except:
## Core Concept
The question tests understanding of spinal cord injuries, specifically the effects of a complete transaction at a specific level, in this case, C7. A complete spinal cord injury results in the loss of all spinal cord function below the level of the injury. This includes loss of motor function, sensation, and autonomic function.
## Why the Correct Answer is Right
A complete transaction of the spinal cord at the C7 level would result in quadriplegia (or tetraplegia), affecting all four limbs, but the extent of respiratory muscle involvement depends on the level of injury. Since the diaphragm (innervated by C3-C5) and some accessory muscles of respiration like the sternocleidomastoid and trapezius (innervated by C2-C7) are still functional, patients can still breathe but may require assistance. The key point here is to identify which of the provided effects is not a consequence of such an injury.
## Why Each Wrong Option is Incorrect
- **Option A:** Loss of motor function below C7. This is a direct consequence of spinal cord injury at C7, as all motor signals below this level are interrupted.
- **Option B:** Loss of sensation below C7. Similar to motor function, sensation (including pain, temperature, touch, vibration, and proprioception) below C7 would be lost due to the interruption of ascending sensory pathways.
- **Option D:** Autonomic dysfunction below C7. This includes loss of bladder and bowel control, as well as sexual dysfunction, due to the interruption of autonomic pathways.
## Clinical Pearl / High-Yield Fact
A critical point to remember is that the level of injury can significantly affect respiratory function. Injuries above C4 often require ventilatory support due to the involvement of the phrenic nerve (C3-C5), which controls the diaphragm. However, at the C7 level, while respiratory function might be compromised, patients might still have some ability to cough and breathe without a ventilator, though they may need assistance.
## Correct Answer: D.