An upper motor neuron lesion of facial nerve will cause: March and September 2007

Ans. B: Paralysis of the lower half of face on the opposite sideCentral facial palsy is a symptom or finding characterized by paralysis 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 (ie, from both sides of the brain).The ventral division receives only contralateral input (ie, from the opposite side of the brain).Thus, lesions of the coicobulbar tract between the cerebral coex and the facial motor nucleus destroy or reduce input to the ventral division, but ipsilateral input (ie, from the same side) to the dorsal division is retained. As a result, central facial palsy (damage to upper motor neurons of the facial nerve) is characterized by hemiparalysis or hemiparesis of the contralateral muscles of facial expression, but not the muscles of the forehead.