Plan of the facial and intermediate nerves and their communication with other nerves. ("Nucleus of Facial N." labeled at upper left.)
|- style="text-align: center;" class="hiddenStructure"
| colspan="2" |
The nucleus has a dorsal and ventral region, with neurons in the dorsal region innervating muscles of the upper face and neurons in the ventral region innervating muscles of the lower face.
Like all lower motor neurons, cells of the facial motor nucleus receive input from the primary motor cortex in the frontal lobe of the brain. Upper motor neurons of the cortex send axons that descend through the internal capsule and synapse on neurons in the facial motor nucleus. This pathway from the cortex to the brainstem is called the corticobulbar tract.
Interestingly, the neurons in the dorsal aspect of the facial motor nucleus receive inputs from both sides of the cortex, while those in the ventral aspect mainly receive contralateral inputs (i.e. from the opposite side of the cortex). The result is that both sides of the brain control the muscles of the upper face, while the right side of the brain controls the lower left side of the face, and the left side of the brain controls the lower right side of the face.
Effects of lesions
As a result of the corticobulbar input to the facial motor nucleus, an upper motor neuron lesion to fibers innervating the facial motor nucleus results in central seven. The syndrome is characterized by flaccid paralysis of the contralateral lower face. For example, a left corticobulbar lesion results in paralysis of the muscles that control the lower right quadrant of the face.
By contrast, a lower motor neuron lesion to the facial motor nucleus results in paralysis of facial muscles on the same side of the injury. This condition is known as Bell's palsy.
