How is a complete spinal cord injury defined?

A complete spinal cord injury is characterized by the permanent loss of all spinal cord-mediated functions below the level of the injury. This means that sensory and motor functions are entirely lost below the affected area, leading to total paralysis (quadriplegia or paraplegia, depending on the location of the injury). The defining aspect of a complete injury is that there is no residual functional ability in the affected segments of the body, which distinguishes it from incomplete spinal cord injuries, where some degree of function remains.

The other options describe different scenarios that do not align with the definition of a complete spinal cord injury. For instance, partial loss of function suggests that some capabilities remain, while temporary loss implies that functionality might return over time, which directly contradicts the permanence associated with a complete spinal cord injury. Additionally, loss of upper body functions only does not encompass the complete lack of function that defines a complete injury, which can affect lower body functions as well. Thus, option B accurately captures the essence of a complete spinal cord injury.