Text Translation 12th of Sep
The facial nerve receives impulses from multiple brain areas. Lower face muscles are represented more fully in the motor cortex than the upper face, allowing for more voluntary and learned control of the lower face; this provides the fine controls of that facial region required for speech articulation. The amount of bilateral v. contralateral fibers to the facial muscles differs depending on region, with the lower face being primarily contralateral and bilateral fibers increasing in the upper face. (Note that there are large individual differences in this regard, and that involuntary expressions for the most part provide bilateral activation.) Voluntary and involuntary expressions are under the control of different neural tracts, with voluntary expressions controlled by impulses from the motor strip through the pyramidal tract, and involuntary expressions controlled by impulses from subcortical areas through the extrapyramidal tract. The activation of facial movements that have become habitual, although acquired voluntarily, might resemble involuntary activation, but no research on this has been reported.