I get why people can control their eyes while paralyzed, but why can they not control the rest of their face usually? I didn’t think those nerves went through the brain stem either.
In: Biology
The eyes are so directly linked to the brain that the retina might even be called part of it.
Your facial muscles are controlled by nerves that are routed from the brain stem, through a hole in the skull under each ear, and to where they’re needed.
The muscles of your face and senses are controlled via cranial nerves, which all originate at different spots. Cranial nerves 1-6, which include the nerves that control the eyes (2, 3, 4, and 6) are located in the cerebellum and midbrain. The nerves that control the rest of the face, 7 and on (with the exception of 5) are in the brainstem (pons and medulla) which go through the big hole at the base of your skull. Obviously the biggest predictor of function is where that lesion is that caused the paralysis, but generally speaking the eye nerves are in the brain, and the face muscles are in the brainstem/spinal cord.
The degree of paralysis depends on the location of the injury to the nervous system. The nerves that control the eye muscles and movements are in a higher part of the brainstem (mostly midbrain) and facial movements are controlled in a lower part of the brainstem (pons). If there is an injury to the area of the brainstem that controls the facial muscles but not the eye muscles, then the face but not the eye movements are paralyzed. If there is an injury to the area of the brainstem that controls the eye muscles then the eye movements will also be paralyzed.
It gets more confusing because the higher parts of the brain also are involved in these processes but this is ELI5 so won’t go further. Neuroanatomy is hard and extremely complex.
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