What is the specialty of corticonuclear (supranuclear) innervation of the facial (cranial nerve VII) and hypoglossal (cranial nerve XII) nuclei compared to other cranial nerve nuclei?

From the Guidelines

The speciality of corticonuclear (supranuclear) innervation of the facial and hypoglossal nuclei compared to other cranial nerve nuclei is their asymmetric bilateral cortical representation, with the upper facial muscles receiving bilateral cortical innervation and the lower facial muscles and tongue receiving predominantly contralateral cortical input. This unique pattern is crucial for understanding the clinical presentation of patients with upper motor neuron lesions, such as stroke, who may experience weakness in the contralateral lower face and tongue while maintaining the ability to wrinkle their forehead and close their eyes bilaterally 1. The facial nucleus (CN VII) and hypoglossal nucleus (CN XII) have a distinct pattern of innervation, with the upper facial muscles (forehead and orbicularis oculi) receiving bilateral cortical input, whereas the lower facial muscles and tongue receive predominantly contralateral cortical input 1. This anatomical arrangement is essential for localizing lesions and distinguishing between upper motor neuron lesions (central) and lower motor neuron lesions (peripheral) affecting facial and tongue movements.

Some key points to consider:

• The facial nerve (CN VII) is one of the most complex cranial nerves, containing branchial motor, visceral motor, general sensory, and special sensory functions 1.
• The hypoglossal nerve (CN XII) nucleus arises in the dorsal medulla and provides somatic motor innervation to the intrinsic and extrinsic muscles of the tongue (except the palatoglossus muscle) and the infrahyoid strap muscles via the ansa cervicalis 1.
• MRI offers excellent soft tissue contrast and directly images the intracranial and skull base segment of CN XII, making it an essential tool for evaluating hypoglossal nerve palsy 1.
• The clinical presentation of hypoglossal nerve palsy can vary, but typically includes dysarthria and deviation of the tongue to the side of the lesion upon tongue protrusion 1.

Overall, understanding the unique pattern of corticonuclear innervation of the facial and hypoglossal nuclei is essential for accurate diagnosis and treatment of patients with cranial nerve palsies.

From the Research

Corticonuclear Innervation of Facial and Hypoglossal Nucleus

The corticonuclear innervation of the facial and hypoglossal nucleus has distinct characteristics compared to other cranial nerve nuclei. Key aspects of this innervation include:

• Bilateral innervation of the lower facial muscles from both sides of the motor cortex 2, 3
• The presence of both oligosynaptic and polysynaptic pathways to lower facial muscles, with the former being predominantly contralateral and the latter being bilateral 3
• The ability of the corticobulbar tract to innervate perioral muscles bilaterally, which contributes to the relatively mild and incomplete nature of central facial palsy caused by a stroke 2

Comparison to Other Cranial Nerve Nuclei

In comparison to other cranial nerve nuclei, the facial and hypoglossal nuclei receive:

• More complex and bilateral corticonuclear innervation, which allows for finer control over facial expressions and movements 2, 3
• Inputs from both hemispheres of the motor cortex, which enables more flexible and adaptive motor control 2, 3

Clinical Implications

The unique characteristics of corticonuclear innervation to the facial and hypoglossal nucleus have important clinical implications, including:

• The potential for rapid recovery from central facial palsy due to cortical reorganization and the bilateral nature of the innervation 2
• The use of botulinum toxin A injections and half-mirror biofeedback exercises as a treatment strategy for facial sequelae after facial paralysis 4