THE MANY FACETS OF THE TONGUE

RELATIONSHIP BETWEEN THE TONGUE AND OTHER BODY SYSTEMS

• During respiration, the hyoid bone moves in a craniocaudal direction, due to the action of the extrinsic muscles of the tongue, causing the pharyngeal space to dilate. In general,  the anterior part of tongue is considered important for non-respiratory activities, while the posterior part is important for respiration.

• Al l the tongue muscles, extrinsic and intrinsic muscle groups, always work synergistically and not separately. The tonus of those muscles must be well-balanced; otherwise dysfunction can occur, resulting in an alteration in the position of the hyoid bone and the functionality of the tongue.

• The tongue position influences the body. If the tongue is positioned against the palate, the parasympathetic system will reduce it systemic activity (for ex., heartbeats and respiratory rhythm increase), but if positioned against the soft palate, the sympathetic system will reduce its activity.

• Tongue movement, generally postero-lateral activate the  anterior Cingulate Cortex (ACC), which plays an important role in the sensory, cognitive, and emotional information and pain processing. ACC is often concerned with visceral sensations.

• The tongue has control on the posture, thanks to its greater tactile sensitivity than the finger.

• The tongue position and its voluntary and involuntary strength might vary with lung volume. Changes in the tracheal traction at different lung volumes may alter the mechanics of the tongue muscles and their ability to produce protrusion force, and these changes in the lung volume alter tension transferred through the trachea to the hyoid arch.

• Tonic tongue muscle activity and movements related to spontaneous respiration increase significantly in the supine position with respect to the upright position.

THE UPPER AIRWAY MUSCLES.

• The upper airway can collapse at one or multiple sites: the pharyngeal structures that can contribute to airway crowding and collapse include the genioglossus, soft palate, lateral pharyngeal walls, and epiglottis.

• The human pharynx is vulnerable to collapse during sleep. There are 20 muscles in the upper airway that are involved in respiratory and non respiratory tasks. A subset of these muscles play a predominant role in airway stability during breathing.

• Activation of the upper airway dilator muscles is effective in opposing the collapsing pressures generated during inspiration. However, during sleep, state-dependent reduction in muscle activity combined with anatomical susceptibility can induce airway collapse.

• The genioglossus, the largest pharyngeal dilator muscle, receives up to 6 different patterns of drive, the summation of which typically results in activation of the muscle. But its activity is reduced during sleep, unlike the tensor palatine muscle (palatal muscle) that is active throughout the breathing cycle.

• Activation alone of the genioglossus is not sufficient to re-open the airway, which goes to show that the involvement of all the upper airway muscles is required for breathing.

source: physio-pedia.com