Tongue movements--brainstem mechanisms and clinical postulates

Area of Science:

• Neuroscience
• Oral Physiology
• Motor Control

Background:

• The hypoglossal nucleus controls tongue movements, crucial for functions like speech and swallowing.
• Understanding neural pathways influencing tongue muscle activity is vital for addressing orofacial disorders.
• Skeletal open-bite malocclusions are often linked to abnormal resting tongue posture.

Purpose of the Study:

• To investigate the specific excitatory and inhibitory neural influences on hypoglossal motoneurons controlling tongue protrusion and retrusion.
• To elucidate the role of sensory input from the temporomandibular joint and oropharyngeal structures in modulating tongue muscle activity.
• To explore the potential of these findings for developing targeted therapies for skeletal open-bite malocclusions.

Main Methods:

• Electrophysiological recordings were performed in cats to study motoneuron responses.
• Stimulation of peripheral nerves, including the auriculotemporal, glossopharyngeal (IX), and superior laryngeal nerves, was employed.
• Responses of genioglossus (GG) single units and protrusive (P) motoneurons were analyzed.

Main Results:

• Stimulation of the auriculotemporal nerve (innervating the temporomandibular joint) activated GG units and P motoneurons.
• Stimulation of glossopharyngeal (IX) and superior laryngeal nerves also activated P motoneurons.
• Tongue stimulation (lingual and IX nerves) elicited retrusive tongue movements.

Conclusions:

• Specific neural pathways from the jaw and oropharynx directly influence hypoglossal motoneurons controlling tongue movement.
• These brainstem mechanisms provide insights into the motor control of tongue posture and movement.
• Findings suggest potential therapeutic targets for skeletal open-bite malocclusions by modulating these neural circuits.