accessory facial motor nucleus

The accessory facial motor nucleus (ACVII) is a small cluster of neurons located dorsal to (above) the main facial motor nucleus in the pontine tegmentum of the brainstem. It contains motor neurons contributing to the facial nerve's (CN VII) motor output.

The accessory facial motor nucleus is situated in the dorsal pons (pontine tegmentum), positioned dorsal to the main facial motor nucleus. Like the main nucleus, it contributes fibers to the facial nerve.

The accessory facial motor nucleus provides additional motor innervation through the facial nerve. The facial nerve controls the muscles of facial expression, the stapedius muscle in the middle ear, the stylohyoid, and the posterior belly of the digastric. This accessory nucleus contributes to these motor outputs.

Lesions affecting the pontine region that include the accessory facial motor nucleus may contribute to lower motor neuron facial palsy (affecting all muscles of facial expression on the same side). Pontine tumors, multiple sclerosis, and vascular events in this region can involve this nucleus.

The main facial motor nucleus is the principal collection of motor neurons for the facial nerve, while the accessory facial motor nucleus is a smaller, supplementary cluster located dorsally. Both contribute to the same nerve, but the accessory nucleus is smaller and may supply a more limited subset of facial muscles.