system
Given the following post, respond as if you're commenting on Reddit:
human
How come diseases and conditions where motor functions of the entire body are lost, but the mind remains intact (such as locked-in syndrome), individuals can still retain minor control over muscles in the face?

Is there a link between muscles in the eyes/cheeks/chin/forehead and the brain that differs from the other muscles in the body? Why is it that even with degenerative diseases, voluntary movement can be entirely lost but still some movement is retained in the head/face/vocal cords?
gpt
So the nerve supply to your face is different than the nerve supply to the extremities. The muscles in your extremities receive innervation, or neurological stimulation, from nerves that originate from motor cortices, while the nerves that innervate the face/cords directly arise from the brain/brainstem itself. To be more clear, the motor cortex itself does not control the face, but it does control the extremities.

This doesn't mean that the cranial nerves themselves won't be affected by the disease, but it means that if the motor cortex is the only thing that has notable damage from the aforementioned disease, then then cranial nerves (CN) may be spared, leaving a portion of the face untouched. 

*as pointed out below, the corticobulbar tract originating in the motor cortex, does provide some innervation to the face.