Family Friendly & Specialty Dentists in London, UK
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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.
