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Central facial palsy is a symptom or finding characterized by paralysis or paresis of the lower half of one side of the face. It usually results from damage to upper motor neurons of the facial nerve.
The facial motor nucleus has dorsal and ventral divisions that contain lower motor neurons supplying the muscles of the upper and lower face, respectively. The dorsal division receives bilateral upper motor neuron input while the ventral division receives only contralateral input.
Thus, lesions of the corticobulbar tract between the cerebral cortex and pons and the facial motor nucleus destroy or reduce input to the ventral division, but ipsilateral input to the dorsal division is retained. As a result, central facial palsy is characterized by hemiparalysis or hemiparesis of the contralateral muscles of facial expression, but not the muscles of the forehead.