Structure and Function of the Facial Motor Nucleus - The nucleus is located in the ventrolateral pontine tegmentum. - Its axons form the motor component of the facial nerve. - Neurons in the dorsal region innervate muscles of the upper face, while neurons in the ventral region innervate muscles of the lower face. - The facial motor nucleus is part of the special visceral efferent (SVE) cell column. - It innervates muscles derived from pharyngeal arches. - It receives cortical input from the primary motor cortex. - Upper motor neurons send axons that synapse on neurons in the facial motor nucleus.

Cortical Input to the Facial Motor Nucleus - Cells of the facial motor nucleus receive cortical input from the primary motor cortex. - Upper motor neurons descend through the internal capsule. - Neurons in the dorsal aspect receive inputs from both sides of the cortex. - Neurons in the ventral aspect mainly receive contralateral inputs. - Both sides of the brain control the muscles of the upper face.

Clinical Significance of Facial Motor Nucleus Lesions - An upper motor neuron lesion to fibers innervating the facial motor nucleus results in central seven. - The syndrome is characterised by spastic paralysis of the contralateral lower face. - A lower motor neuron lesion to the facial motor nucleus results in paralysis on the same side of the injury. - Idiopathic palsy is the term used when the cause cannot be identified. - Bells palsy is the term used when the cause is known.

Mechanism of Facial Nerve Upper vs Lower Motor Neuron Lesions - Lesions within the corticobulbar tract are upper motor neuron lesions. - Lesions affecting the individual branches are lower motor neuron lesions. - The facial nerve branches leave the facial motor nucleus via different routes. - The temporal branch receives motor input from both hemispheres. - The zygomatic, buccal, mandibular, and cervical branches receive input from only contralateral hemispheres.

Additional Details about the Facial Motor Nucleus - The nucleus has a dorsal and ventral region. - Its axons travel dorsally and loop around the abducens nucleus. - It is considered along with the trigeminal motor nucleus, nucleus ambiguus, and spinal accessory nucleus.