Final answer:
Even with a severed spinal cord at the base of the skull, a cat can still execute walking movements on a treadmill because of central pattern generators in the spinal cord that can control these movements without direct brain input, thanks to sensory feedback from the treadmill and external support.
Step-by-step explanation:
When a cat's spinal cord is severed at the base of the skull, the connection between the brain and the body below the point of injury is lost, leading to paralysis. However, walking is a coordinated set of muscle contractions that can be mediated by neural circuits within the spinal cord itself, below the level of injury, known as central pattern generators (CPGs). These CPGs can control complex muscle movements without direct brain input.
While the cat cannot stand due to the paralysis caused by the severed spinal cord, when placed on a treadmill, the sensory feedback from the moving belt can activate the CPGs in the spinal cord. As a result, the cat can still execute the motor patterns of walking, trotting, and running, thanks to these intact spinal circuits and the external support provided by the harness.
It's important to note that these movements are not consciously controlled by the cat's brain but are rather reflexive responses due to the stimulation of neural circuits within the spinal cord.