Central seven

Central seven, also called central facial palsy, is a disease 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 corticobulbar tract between the cerebral cortex and the facial motor nucleus destroy all input to the ventral division, but ipsilateral input (ie, from the same side) to the dorsal division is retained. As a result, central seven is characterized by hemiparalysis of the contralateral muscles of facial expression.

Actor Sylvester Stallone has central seven on the left side of his face, caused by birth complications.