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Obstructive sleep apnea (OSA) is more common in patients with asthma, and inhaled corticosteroids may contribute to OSA pathogenesis in these patients. This study tested the effects of orally inhaled fluticasone propionate (FP) on extrinsic tongue muscles. Unanesthetized rats were treated with FP or placebo for 28 days. On day 29, tongue retrusive and protrusive functions were tested via hypoglossal nerve stimulation under a state of anesthesia, followed by genioglossus (GG), styloglossus (SG) and hyoglossus (HG) muscle extraction, after euthanasia, for histology [myosin heavy chain (MHC) fibers and laminin content reflecting extracellular matrix (ECM)]. On protrusive testing, FP increased percent maximum tetanic force at 40 Hz ( P = 0.03 vs. placebo) and endurance index ( P = 0.029 vs. placebo). On retrusive testing, FP increased maximum twitch ( P = 0.026 vs. placebo) and tetanic forces ( P = 0.02 vs. placebo) with no effect on endurance index. On histology, FP increased GG cross-sectional area of MHC type IIa ( P = 0.036 vs. placebo) and tended to increase type IIb ( P = 0.057 vs. placebo) fibers and HG MHC IIx fibers ( P = 0.065). The FP group had significantly increased laminin-stained areas, of greatest magnitude in the HG muscle. FP affects tongue protrusive and retrusive functions differently, concurrent with a shift in MHC fibers and increased ECM accumulation. These differential alterations may destabilize the tongue’s “muscle hydrostat” during sleep and promote collapse. NEW & NOTEWORTHY The effects of inhaled corticosteroid on upper airway may contribute to OSA pathogenesis in asthma. In this study, we tested the effects of orally inhaled fluticasone propionate on tongue protrusive and retrusive functions and on tongue extrinsic muscle fiber composition and molecular properties. We found that fluticasone treatment: 1) increased protrusive endurance and retrusive maximum twitch and tetanic force; and 2) on histology, increased cross-sectional area of myosin heavy chain (MHC) type IIa fibers and tended to increase cross-sectional area of MHC type IIb fibers in the protrusive muscle and of MHC IIx fibers in the retrusors. It also increased laminin-stained areas, across extrinsic tongue muscles, of greatest magnitude in the retrusors; and 3) reduced protein degradation and activated pathways associated with increased protein synthesis in the protrusor. These differential effects on the protrusors and retrusors may destabilize the tongue’s “muscle hydrostat” properties during sleep and promote collapse.

Purpose: Exercise-based treatment approaches for dysphagia may improve swallow function in part by inducing adaptive changes to muscles involved in swallowing and deglutition. We have previously shown that both aging and progressive resistance tongue exercise, in a rat model, can induce biological changes in the genioglossus (GG); a muscle that elevates and protrudes the tongue. However, the impacts of progressive resistance tongue exercise on the retrusive muscles (styloglossus, SG; hyoglossus, HG) of the tongue are unknown. The purpose of this study was to examine the impact of a progressive resistance tongue exercise regimen on the retrusive tongue musculature in the context of aging. Given that aging alters retrusive tongue muscles to more slowly contracting fiber types, we hypothesized that these biological changes may be mitigated by tongue exercise.Methods: Hyoglossus (HG) and styloglossus (SG) muscles of male Fischer 344/Brown Norway rats were assayed in age groups of young (9 months old, n = 24), middle-aged (24 months old, n = 23), and old (32 months old, n = 26), after receiving an 8-week period of either progressive resistance protrusive tongue exercise, or sham exercise conditions. Following exercise, HG and SG tongue muscle contractile properties were assessed in vivo. HG and SG muscles were then isolated and assayed to determine myosin heavy chain isoform (MyHC) composition.Results: Both retrusive tongue muscle contractile properties and MyHC profiles of the HG and SG muscles were significantly impacted by age, but were not significantly impacted by tongue exercise. Old rats had significantly longer retrusive tongue contraction times and longer decay times than young rats. Additionally, HG and SG muscles showed significant MyHC profile changes with age, in that old groups had slower MyHC profiles as compared to young groups. However, the exercise condition did not induce significant effects in any of the biological outcome measures.Conclusion: In a rat model of protrusive tongue exercise, aging induced significant changes in retrusive tongue muscles, and these age-induced changes were unaffected by the tongue exercise regimen. Collectively, results are compatible with the interpretation that protrusive tongue exercise does not induce changes to retrusive tongue muscle function.

BACKGROUND AND PURPOSE: When optimising radiotherapy treatments today, the pharyngeal constrictor muscles and the larynx are usually regarded as the swallowing organs at risk (SWOARs). The purpose of this study was to identify and describe additional, previously undefined groups of muscles (functional units) involved in crucial components of swallowing (hyolaryngeal elevation (HLE), tongue base retraction (TBR) and tongue motion), and to emphasise their relevance in radiation-induced dysphagia.MATERIAL AND METHODS: Based on available literature on human anatomy and swallowing physiology, the functional units of muscles involved in HLE, TBR and tongue motion have been identified and described.RESULTS AND CONCLUSION: Functional swallowing units (FSUs) were defined as groups of swallowing muscles sharing their function, that are in close proximity to each other. Seven FSUs involved in HLE, TBR and tongue motion were identified: floor of mouth, thyrohyoid muscles, posterior digastric/stylohyoid muscles complex, longitudinal pharyngeal muscles, hyoglossus/styloglossus muscles complex, genioglossus muscles, intrinsic tongue muscles. The swallowing physiology and anatomy of the FSUs described in this paper will lead to a greater understanding of radiation-induced dysphagia mechanisms and, consequently, to an improvement in the development of swallowing sparing strategies. This article (PART 1) serves as the theoretical foundation for a subsequent article (PART 2), which provides detailed delineation guidelines for FSUs.

Objective To determine whether muscle invasion evident on pretreatment imaging in p16 + oropharyngeal squamous cell carcinoma (OPSCC) correlates with recurrence. Study design Retrospective review. Methods Two-hundred and seventy-six patients with p16 + OPSCC treated at a tertiary referral center from 2003 to 2015 were analyzed. All scans were reviewed by a dedicated neuroradiologist with subspecialty expertise in head and neck imaging. Radiographic evidence of muscle invasion to the genioglossus, hyoglossus, medial pterygoid, and prevertebral muscles was analyzed. Local and regional recurrence rates were compared between the muscle invasion and no muscle invasion groups. Results One hundred and ninety patients met inclusion criteria with adequate follow-up data and pretreatment imaging. Patients were predominantly male (87.5% male) and smokers (65.6% smokers) with a mean age of 56.7 (standard deviation: 9.0 years). Most commonly invaded muscles in the muscle invasion group were hyoglossus (57.8%) and genioglossus (56.3%). There was no statistically significant difference in primary site or nodal recurrence between the combined group, including definite or possible muscle invasion and the group without muscle invasion (P = 0.205 and P = 0.569, respectively). Additionally, no statistically significant difference was present in recurrence-free and disease-specific survival between the two groups at 3- and 5-year follow-up (P > 0.05). Conclusion Radiographic evidence of muscle invasion does not appear to be a predictor of human papilloma virus (+) OPSCC recurrence. Additional studies are needed to validate our findings. Level of evidence 4 Laryngoscope, 129:871-876, 2019.

The tongue is a dense muscular organ, in which the muscles are arranged in a confusing pattern. The intrinsic muscles were gross anatomically investigated in 25 cadavers to clarify their configuration. The superior longitudinal muscle (SLm) ran beneath the dorsal mucosa and was divided into bundles by the other muscles passing through it to the dorsum. The external bundle of the styloglossus, with the palatoglossus, coursed externally to the hyoglossus. Their fibers spread beneath the SLm or attached to the apex and the inferior longitudinal muscle (ILm) ascended from the root and joined them. The genioglossus and the anterior part of the hyoglossus extended internally and externally to the ILm, respectively, to the dorsum, and the vertical muscle was sandwiched between them. The transverse muscle passed laterally from the lingual septum. The fibers of the posterior part of the hyoglossus converged to the root and spread beneath the SLm. The intersections between these vertical and transverse fibers divided one another into bundles or lamellae. The middle bundle of the styloglossus, passing between the two parts of the hyoglossus, was divided into slips by the intersection with the genioglossus. The internal bundle of the styloglossus, with the glossopharyngeus, descended internally to the posterior part to the root. The findings indicate that the intrinsic and extrinsic muscles of the tongue are not independent groups, and their fibers form a three-dimensional latticework. Each muscle contains numerous bundles or lamellae as functional units that can act separately or cooperate across the muscles.

Our aim was to find out first whether the extrinsic muscles of the tongue are histologically identifiable, and secondly to what degree the use of the new criteria in the 8th editions of the American Joint Committee on Cancer(AJCC)/Union for International Cancer Control (UICC) manuals (which have recognised the importance of depth of invasion of tumour, rather than invasion of the extrinsic muscles of the tongue and extranodal extension), will alter staging of lingual squamous cell carcinoma (SCC). The histological sections from 165 patients who had had primary resection of lingual SCC were reviewed, and one or more extrinsic muscles of the tongue was identified in 100 patients (61%), with the genioglossus seen the most often (in 96). By contrast, the hyoglossus was identified in only eight patients, the styloglossus in two, and the palatoglossus in none. Identification was straightforward only in extensive resections. Applying the criteria from the 8th edition increased the number of pT3 SCC with a simultaneous reduction in pT4a tumours. The number of pN2b SCC was also reduced, but the new category of pN3b meant that overall 53% of tumours were upstaged. The kappa scores for agreement between the two sets of criteria were 0.221 (weighted 0.410) for the pT values, 0.508 (0.713) for pN values (but 0.227, weighted 0.386, if the pN0 values were removed before calculation), and 0.243 (0.514) for overall stage, indicating poor to fair agreement. We conclude that the removal of invasion of extrinsic muscles of the tongue as a criterion for a pT4a SCC is justified, and that many SCC of the tongue will be upstaged as a result of implementation of the 8th editions.

There are increased risks for deglutition disorders in people with Down syndrome (DS). Although mouse models have been used to study the biological underpinnings of DS in other areas, relatively little is known about swallowing phenotypes in these models. We hypothesized that swallowing performance would be affected in adult mouse models of DS, relative to typical control mice. Videofluoroscopic swallow studies (VFSS) were conducted on adults of two mouse models of DS: Ts65Dn and Dp(16)1Yey, and evaluated in comparison with age-matched controls. Relative to other groups, adult Ts65Dn showed significantly slower swallow rates, longer inter-swallow intervals (ISI), and greater numbers of jaw excursion cycles preceding each swallow. In contrast, adult Dp(16)1Yey mice showed swallowing performance similar to control mice. Exploratory quantitative analyses of the intrinsic tongue (transverse muscle), and extrinsic tongue muscles [genioglossus (GG), styloglossus (SG), and hyoglossus (HG)] showed no significant differences between genotype groups in myosin heavy chain isoform profiles. Collectively, these findings suggest that while swallowing is typical in adult Dp(16)1Yey, swallowing in adult Ts65Dn is atypical due to unknown causes. The finding that adult Ts65Dn may have utility as a model of dysphagia provides new opportunities to elucidate biological underpinnings of dysphagia associated with DS.

Objectives/hypothesis Upper airway stimulation for obstructive sleep apnea (OSA) via implantable hypoglossal nerve stimulation (HGNS) reduces airway obstruction by selectively stimulating nerve fibers that innervate muscles that produce tongue protrusion, while avoiding fibers that produce tongue retraction. This selective stimulation likely depends upon the location, intensity, and type of electrical stimulation delivered. This study investigates the impact of changing stimulation parameters on tongue muscle activation during HGNS using intraoperative nerve integrity monitoring in conjunction with electromyography (EMG). Study design Prospective case series. Methods Ten patients undergoing unilateral HGNS implantation for OSA in a university hospital setting were studied. Data included EMG responses in tongue muscles that produce protrusion (genioglossus), retraction (styloglossus/hyoglossus), and stiffening (transverse/vertical) in response to intraoperative bipolar probe electrical stimulation of lateral and medial branches of the hypoglossal nerve (HGN) and to implantable pulse generator (IPG) unipolar and bipolar settings after placement of the stimulation cuff. Results Stimulation of medial division HGN branches resulted in EMG responses in genioglossus muscles, but not in styloglossus/hyoglossus muscles, whereas stimulation of the lateral division HGN branches drove responses in styloglossus/hyoglossus muscles. Variable responses in transverse/vertical muscles were observed with stimulation of lateral and medial division branches. After electrode cuff placement, unipolar and bipolar HGN stimulation configurations of IPG resulted in unique patterns of muscle activation. Conclusions The relative activation of extrinsic and intrinsic tongue musculature by HGNS is determined by stimulus location, intensity, and type. Intraoperative neurophysiological monitoring of tongue muscle activation enables proper electrode cuff placement and may provide essential data for stimulus optimization. Level of evidence 4 Laryngoscope, 130:1836-1843, 2020.

Three hypothetical models of tongue movement of the walrus during suction feeding are examined. These models encompass the entire range of simple tongue retraction movements possible by examining 1) movement of the tongue directly to the rear following the curvature of the palate, 2) to the rear and ventrally in a straight line, and 3) ventrally in a straight line. The percent of muscular force available from the hyoglossus, genioglossus, and styloglossus that could be applied toward retraction as predicted by each model is calculated. The resistance that the tongue would provide during retraction is calculated using projected tongue areas and is combined with the above data from the muscles to provide an estimate of the percent of the total available force that is needed to retract the tongue for each model. A separate examination of the direction of tongue-induced wear striations on the palatal and lingual aspects of the teeth is used to help support or reject the three models. The model where the tongue is moved directly to the rear is supported by studies of both muscle force and tooth wear. In the mammalian groups that were compared to the walrus, there is a great deal of interspecific variation in movements of the tongue during suction feeding; no two groups can be considered to have identical stereotyped tongue movements.

Little is known about the anatomy and musculature of the gray whale (Eschrichtius robustus), especially related to the anatomy of the tongue and hyoid region. The recovery of an extremely fresh head of a neonatal female gray whale provided an opportunity to conduct the first in-depth investigation of the musculoskeletal features of the tongue and hyoid apparatus. Unlike other mysticetes, the gray whale tongue is strong, muscular, and freely mobile inside the buccal cavity. In particular, the genioglossus and hyoglossus muscles are extremely large and robust making up the majority of the body of the tongue. In addition, the genioglossus had a unique position and fiber orientation in the tongue compared to other mammals. The structure of the hyoid apparatus differs between E. robustus and other mysticete species, although there are similarities among individual elements. We provide the first documentation of fungiform papillae that may be associated with taste buds in Mysticeti. The highly mobile, robust tongue and the presence of well-defined tongue and hyoid musculature are in keeping with observations of gray whale feeding that suggest this group of whales utilize oral suction to draw benthic prey into the buccal cavity. Anat Rec, 298:660–674, 2015. © 2014 Wiley Periodicals, Inc.

The hypoglossal or twelfth cranial nerve is the motor nerve to the extrinsic and intrinsic muscles of the tongue, and the superior root of the ansa cervicalis and the thyrohyoid and geniohyoid branches are delivered through the nerve. This study investigated the muscular branches of the hypoglossal nerve to clarify their spatial relationships with the muscles of the tongue and the neighboring structures. The muscles and the nerve were gross anatomically examined in 42 cadavers. The superior root and the thyrohyoid branch left the nerve near the occipital and lingual arteries, respectively. The extrinsic muscles consisted of some components, and the geniohyoid branch and the lingual branches arose on the hyoglossus. The ascending lingual branches formed a plexus on the anterior part of the hyoglossus and were divided into the proximal and distal groups. They supplied the two parts of the hyoglossus, the three bundles of the styloglossus and the superior and inferior longitudinal muscles and communicated with the lingual nerve. The descending lingual branches supplied the inferior part of the genioglossus, and the terminal branches gave intramuscular twigs to its main part and the transverse and vertical muscles. The findings indicated that the branching pattern of the hypoglossal nerve is characterized by the positional relationships to the components of the extrinsic muscles. The hyoid bone can be an effective marker to identify the branches and affected position if it was used in combination with the morphology of the extrinsic muscles, and the knowledge of their variations is also beneficial. Anat Rec, 302:558-567, 2019. © 2018 Wiley Periodicals, Inc.

The TNM classification for oral malignancies has been criticized for its upstaging to T4a when tumour involves styloglossus, hyoglossus, palatoglossus and genioglossus. The aims of this study were to (1) create an anatomical computer atlas of extrinsic tongue musculature, and (2) reassess the original staging of pre-treatment archived magnetic resonance images (MRI) of tongue carcinomas using the strict extrinsic muscle criteria. The anatomy of the extrinsic tongue muscles was mapped using images from the Visible Human Project (VHP) to create a computer model of the extrinsic tongue muscles. This was co-registered with 87 archived pre-staging MRI scans of tongue carcinomas to assess tumour ingress of the extrinsic tongue muscles. Of the 87 image sets reviewed, 16 were of superficial tumours not visible on MRI. In the remaining 71 cases that showed positive extrinsic muscle tumour ingress, 52% were upstaged from T1/2/3 tumours to cT4a based upon this finding. Extrinsic lateral and genioglossus muscle invasion did not predict occult cervical lymph node invasion or disease-related survival. In conclusion, tumour invasion of styloglossus or hyoglossus would result in the majority of lateral tongue tumours being staged T4a. Such stratification is of little clinical relevance, and an alternative more reliable method is required.

The base of tongue plays an important role in the pathophysiology of obstructive sleep apnea (OSA), and addressing the tongue base can be an alternative for continuous positive airway pressure and some surgeries done such as uvulopalatopharyngoplasty to treat OSA. One of the options to address the tongue base to treat the OSA is stimulation of human hypoglossal nerve with implantable devices. Thus, one needs to know the physiology of the human hypoglossal nerve to understand the mechanism of such devices. The human hypoglossal nerve is the primary motor nerve that innervates 7 of the 8 extrinsic and intrinsic muscles of the tongue on each side, except palatoglossus muscle, which is innervated by the ipsilateral vagus nerve. At the level of the hyoid bone, the human hypoglossal nerve (the proximal and midthird) is normally unfasciculated, becoming fascicular only in its distal third where it branches. The lateral branch has many small, independent branches that supply the styloglossus, hyoglossus, and inferior longitudinalis muscles. The medial branch innervates the genioglossus, superior longitudinalis, transversalis, and verticalis muscles.

The tongue is a highly muscular organ, and the extrinsic muscles of the tongue overlap one another, which makes their configuration intricate. The aim was to clarify their spatial interrelationships. The extrinsic muscles of the tongue were gross anatomically investigated in 42 cadavers. The hyoglossus consisted of two parts arising from the hyoid body and the greater horn, respectively. They ascended to the tongue external to the genioglossus. The quadrilateral anterior part contained several parallel bundles, and the triangular posterior part comprised of three bundles converging to the insertion. The genioglossus consisted of many compartments. Although its fibers radiated from the mental spine to the tongue internal to the inferior longitudinal muscle, the lateral fibers of the inferior parts passed externally to it, and the most inferior part attached to the hyoid bone and the epiglottis. The chondroglossus arising from the lesser horn ascended internally to the lateral fibers of the inferior parts. The styloglossus arising from the styloid process coursed externally and internally to the hyoglossus and between its two parts. The external and internal bundles fused with the fibers of the palatoglossus and the superior pharyngeal constrictor, respectively. Three bundles were inserted into the apex with the inferior longitudinal muscle or joined the inferior parts of the genioglossus. The extrinsic muscles are subdivided into small groups of fibers depending on their spatial interrelationships, suggesting that they contain many functional units. Some units act separately, and others cooperate across the traditional boundaries of the muscles.

This study reports an investigation of the well-known context-dependent variation in English /r/ using a biomechanical tongue-jaw-hyoid model. The simulation results show that preferred /r/ variants require less volume displacement, relative strain, and relative muscle stress than variants that are not preferred. This study also uncovers a previously unknown mechanism in tongue biomechanics for /r/ production: Torque in the sagittal plane about the mental spine. This torque enables raising of the tongue anterior for retroflexed [Symbol: see text] by activation of hyoglossus and relaxation of anterior genioglossus. The results provide a deeper understanding of the articulatory factors that govern contextual phonetic variation.

UNLABELLED With 8 figures SUMMARY This study aimed at revealing the origin, course and distribution of the hypoglossal nerve in 20 adult male New Zealand rabbits. In all the animals dissected, the hypoglossal nerve arose from the ventrolateral side of the medulla oblongata with two main roots and gave off a descending branch to the ansa cervicalis before reaching the division of the common carotid artery. This branch was not seen on the right side of only one case. At the lateral aspect of the hyoglossus muscle, the nerve then divided into the lateral and medial main branches, sent branches to the styloglossus, hyoglossus, genioglossus and geniohyoideus muscles and terminated in the intrinsic tongue muscles. A communicating branch was observed between the hypoglossal and accessory nerves in the right side of one animal and between the hypoglossal nerve and the ganglion nodosum in the right retropharyngeal area of another animal. An additional branch was observed innervating the stylohyoideus muscle in one animal only. A lateral lingual-hypoglossal communication was also seen between the lateral branch of the hypoglossal nerve and terminal branches of the lingual nerve.

The respiratory central pattern generator distributes rhythmic excitatory input to phrenic, intercostal, and hypoglossal premotor neurons. The degree to which this input shapes motor neuron activity can vary across respiratory muscles and motor neuron pools. We evaluated the extent to which respiratory drive synchronizes the activation of motor unit pairs in tongue (genioglossus, hyoglossus) and chest-wall (diaphragm, external intercostals) muscles using coherence analysis. This is a frequency domain technique, which characterizes the frequency and relative strength of neural inputs that are common to each of the recorded motor units. We also examined coherence across the two tongue muscles, as our previous work shows that, despite being antagonists, they are strongly coactivated during the inspiratory phase, suggesting that excitatory input from the premotor neurons is distributed broadly throughout the hypoglossal motoneuron pool. All motor unit pairs showed highly correlated activity in the low-frequency range (1–8 Hz), reflecting the fundamental respiratory frequency and its harmonics. Coherence of motor unit pairs recorded either within or across the tongue muscles was similar, consistent with broadly distributed premotor input to the hypoglossal motoneuron pool. Interestingly, motor units from diaphragm and external intercostal muscles showed significantly higher coherence across the 10–20-Hz bandwidth than tongue-muscle units. We propose that the lower coherence in tongue-muscle motor units over this range reflects a larger constellation of presynaptic inputs, which collectively lead to a reduction in the coherence between hypoglossal motoneurons in this frequency band. This, in turn, may reflect the relative simplicity of the respiratory drive to the diaphragm and intercostal muscles, compared with the greater diversity of functions fulfilled by muscles of the tongue.

Obstruction of the upper airway (UA) is associated with episodes of hypoxia and upper airway negative pressure (UANP). In the companion paper it is shown that episodic hypoxia elicits long-term facilitation (LTF) of tongue protrudor, retractor and respiratory pump muscle activity. However, whether repeated exposure to UANP also induces LTF is unknown. We hypothesized that repetitive exposure to UANP would induce LTF of UA and respiratory pump muscle activity and when coupled with hypoxia, as occurs when the UA obstructs, would lead to an even greater facilitation of muscle activity and the response to UANP. Experiments were performed in 24 anaesthetized, spontaneously breathing rats with intact vagi. To induce LTF, UANP stimuli (−10 cmH2O) of 5 s duration were delivered every 30 s for 3 min (± hypoxia). This was repeated eight times over 1 h, each 3 min episode separated by 5 min of normoxia. Genioglossus (GG), hyoglossus (HG) and diaphragm (Dia) muscle activity was recorded before, during and for 1 h following the last exposure to episodic UANP alone (n= 8), UANP and hypoxia together (n= 8) or normoxia alone (n= 8). During the final hour, single pulses of UANP were applied at 1 min and every 10 min thereafter to determine whether LTF of the response to UANP had been induced. Our results show that LTF of GG muscle activity and its response to UANP was induced following exposure to episodic UANP stimuli alone and UANP applied during hypoxia. However, there was no significant difference between these responses. Episodic UANP alone also induced LTF of HG muscle activity but this effect did not manifest until 40 min following the last episode of repeated UANP stimulation. In the presence of hypoxia, no LTF of HG muscle response to UANP was found. In conclusion, episodic UANP stimulation induces LTF of UA dilator and retractor tongue muscles, but no further facilitation occurs when coupled with hypoxia. This response may serve as an important protective mechanism of respiratory homeostasis during sleep, particularly in patients who suffer from obstructive sleep apnoea.

We performed these experiments to determine if repeated exposure to episodic hypoxia induces long term facilitation (LTF) in anaesthetized spontaneously breathing rats. A previous study in spontaneously breathing rats was unable to demonstrate evidence of LTF with repeated hypoxia, but this may have been due to the low number of hypoxic episodes used. We hypothesized that with sufficient exposure, episodic hypoxia LTF of genioglossus (GG), hyoglossus (HG) and diaphragm (Dia) activities would be elicited. Experiments were performed in 24 anaesthetized spontaneously breathing rats with intact vagi. Peak and tonic GG, HG and Dia EMG activities were recorded before, during and for 1 h following exposure to eight (n= 8) or three (n= 8) episodes of isocapnic hypoxia (= 0.1) each of 3 min duration. A third time control series was also performed with exposure to normoxia alone (= 0.28, n= 8). Short-term potentiation of GG and HG muscle activity developed during the early period after repeated exposure to eight and three hypoxic episodes. LTF, however, occurred only after eight hypoxic episodes. This manifested as an increase in peak GG and Dia inspiratory muscle activity and tonic HG activity. LTF of respiratory breathing frequency was also induced, reflected by a reduction in inspiratory and expiratory time. These findings support our initial hypothesis that LTF in the anaesthetized, spontaneously breathing rat is dependent on the number of exposures to hypoxia and show that the responses to repetitive hypoxia are composed of both short and long-term facilitatory changes.

The present study evaluated the effect of coactivation of tongue protrusors and retractors on pharyngeal patency in patients with obstructive sleep apnea. The effect of genioglossus (GG), hyoglossus (HG), and coactivation of both on nasal pressure (Pn):flow relationships was evaluated in a sleep study (SlS, n = 7) and during a propofol anesthesia study (AnS, n = 7). GG was stimulated with sublingual surface electrodes in SlS and with intramuscular electrodes in AnS, while HG was stimulated with surface electrodes in both groups. In the AnS, the cross-sectional area (CSA):Pn relationships was measured with a pharyngoscope to estimate velopharyngeal compliance . In the SlS, surface stimulation of GG had no effect on the critical pressure (Pcrit), HG increased Pcrit from 2.8 ± 1.7 to 3.7 ± 1.6 cmH2O, but coactivation lowered Pcrit to 0.2 ± 1.9 cmH2O ( P < 0.01 for both). In the AnS, intramuscular stimulation of GG lowered Pcrit from 2.6 ± 1.3 to 1.0 ± 2.8 cmH2O, HG increased Pcrit to 6.2 ± 2.5 cmH2O ( P < 0.01), and coactivation had a similar effect to that of GG (Pcrit = 1.2 ± 2.4 cmH2O, P < 0.05). None of the interventions affected significantly velopharyngeal compliance. We conclude that the beneficial effect of coactivation depends on the pattern of GG fiber recruitment: although surface stimulation of GG failed to protrude the tongue, it prevented the occlusive effect of the retractor, thereby improving pharyngeal patency during coactivation. Stimulation of deeper GG fibers with intramuscular electrodes enlarged the pharynx, and coactivation had no additive effect.

The histology and morphology characteristics of the tongue in Scincella tsinlingensis were studied by light and electronic microscopy. Under light microscopy, the tongue consists of tip, lingual body and radix in sequence. Numerous lingual papillae widely distribute on the surface of the dorsal and ventral flanks in the tongue, in addition to some regions of the tip. The papillae's surface is covered with the epithelial layer. The lamina propria and dense connective tissue are distinct existing under the epithelial layer. There are many lingual glands spread over the lamina propria. Tongue muscle is developed and composed of distinct intrinsic muscle, hyoglossus and genioglossus. By scanning electron microscopy, at higher magnification, the epithelial cells of the dorsal surface in the divaricate tongue tips show numerous microvilli, micro-ridges and micro-pores. The surface of dorsal side of the papillae in lingual body is covered with abundant of micro-ridges and taste bud lacuna. On the surface of the papillae in radix, micro-facets and micro-ridges are compactly distributed, as well as scattered mucilage-pores. The lingual epithelium is divided into four layers observed by the transmission electron microscope. Cells of basal layer are irregularly elliptical in shape, with sparse organelles in the cytoplasm. The deep intermediate layer is not always distinct. Small numbers of organelles are scattered into the cytoplasm. The cells of the superficial intermediate layer gradually flatten, as do their nuclei. The cytoplasm contains many keratohyalin granules. Cell membranes are formed processes around cells and joined by abundant desmosomes to the cell membranes of adjacent cells. The cells located on the extreme free-surface side of the keratinized layer have fallen off. The basal lamina is intercalated between the basal layer and the lamina propria. The lamina propria of lingual body contains lingual gland. A large part of the cytoplasm is occupied by mucus granules which located in the distal part of the cell. The connective tissue contains myelinated nerve fibers, vessel and muscle cells.

Background Neurostimulation of the hypoglossal nerve has shown promising results in the treatment of obstructive sleep apnea. This anatomic study describes the detailed topography of the hypoglossal nerve's motor points as a premise for super-selective neurostimulation in order to optimize results and minimize the risk of complications related to main nerve trunk manipulation. Methods Thirty cadaveric hypoglossal nerves were dissected and characterized by number of branches, arborization pattern, and terminal branch motor point location. For each motor point, the distance to cervical midline (x axis), distance to posterior aspect of the symphysis (y axis), and depth from the plane formed by the inferior border of symphysis and anterior border of hyoid (z axis) were recorded. Results The average number of distal branches for each hypoglossal nerve was found to be 9.95 ± 2.28. The average number of branches per muscle was found to be 3.3 ± 1.5 for the hyoglossus muscle, 1.8 ± 0.9 for the geniohyoid muscle, and 5.0 ± 1.6 for the genioglossus muscle. It was found that branches to the genioglossus and geniohyoid muscles were located closer to midline (relative lengths of 0.19 ± 0.07 and 0.19 ± 0.05, respectively) while hyoglossus branches were located more laterally (0.38 ± 0.10 relative length). On the y-axis, the branches to the genioglossus were the most anterior and therefore closest to the posterior symphysis of the mandible (relative length of 0.48 ± 0.11), followed by the geniohyoid (0.66 ± 0.09), and the hyoglossus (0.76 ± 0.16). The branches to the geniohyoid were the most superficial (relative length of 0.26 ± 0.06), followed by the genioglossus (0.36 ± 0.09), and finally, the hyoglossus branches (0.47 ± 0.11), which were located deeply. Conclusion A topographical map of the hypoglossal nerve terminal motor points was successfully created and could provide a framework for the optimization of the neurostimulation techniques.

Rationale: Historically, respiratory-related research in sleep apnea has focused exclusively on the extrinsic tongue muscles (i.e., genioglossus, hyoglossus, and styloglossus). Until recently, the respiratory control and function of intrinsic tongue muscles (i.e., inferior and superior longitudinalis, transverses, and verticalis), which comprise the bulk of the tongue, were unknown. Objectives: The current study sought to determine if extrinsic and intrinsic tongue muscles are coactivated in conditions of hypoxemia comparable to that experienced by adults with obstructive sleep apnea. Measurements: Esophageal pressure and EMG activity of an extrinsic (hyoglossus) and an intrinsic (superior longitudinal) tongue muscle were studied in anesthetized, tracheotomized, spontaneously breathing rats. Average EMG activity was compared in a control gas condition (PaO2, 160 ± 12 mm Hg) and in mild isocapnic hypoxia (PaO2, 69 ± 7.2 mm Hg), with and without brief (3-breath) airway occlusions, pre- and postbilateral vagotomy. Main Results: (1) intrinsic and extrinsic tongue muscles are coactivated in mild hypoxia, (2) airway occlusion increased the activities of intrinsic retractor muscles in mild hypoxia, and (3) extrinsic retractor muscles have a steeper rate of rise of activity and an earlier burst onset relative to intrinsic retractor activities in mild hypoxia. Conclusions: These findings support our working hypothesis that airway patency is maintained not simply by activation of extrinsic tongue muscles but by the coactivation of intrinsic and extrinsic protrudor and retractor muscles.

Laboratory rats were acutely implanted with an electrode array composed of eight independently controllable contacts applied to ventral and dorsal aspects of the left and right hypoglossal nerves (HGNs) and their branches. Bipolar intramuscular electromyographic (EMG) electrodes were implanted into the left and right genioglossus, hyoglossus and styloglossus muscles to identify which muscles were activated during stimulation via the contacts. Elicited movements, including changes in the position of the tongue and in the size and the shape of the airway, were documented video-graphically through a surgery microscope and an endoscope. Constant current electrical stimulation activated various combinations of electrode contacts and the stimulation patterns were correlated with corresponding oral movements, airway sizes, and EMG activities. Results demonstrate that graded responses and differential activation of the various tongue muscles are achievable by stimulation of specific contacts in the electrode array. These effects are interpreted to result from the targeted activation of regions of the nerve lying under and between the electrodes. Further testing established that the muscle responses elicited by unilateral electrical stimulation with the present approach can be smoothly graded, that the muscle responses resulted in opening of the airway and could be reliably maintained for long durations.

Obstructive sleep apnea (OSA) patients have increased upper airway muscle activity, including such lingual muscles as the genioglossus (GG), geniohyoid (GH), and hyoglossus (HG). This adaptation partially protects their upper airway against obstructions. Rodents are used to study the central neural control of sleep and breathing but they do not naturally exhibit OSA. We investigated whether, in chronically instrumented, behaving rats, disconnecting the GH and HG muscles from the hyoid (H) apparatus would result in a compensatory increase of other upper airway muscle activity (electromyogram, EMG) and/or other signs of upper airway instability. We first determined that, in intact rats, lingual (GG and intrinsic) muscles maintained stable activity levels when quantified based on 2 h-long recordings conducted on days 6 through 22 after instrumentation. We then studied five rats in which the tendons connecting the GH and HG muscles to the H apparatus were experimentally severed. When quantified across all recording days, lingual EMG during slow-wave sleep (SWS) was modestly but significantly increased in rats with surgically altered upper airway [8.6 ± 0.7% (SE) vs. 6.1 ± 0.7% of the mean during wakefulness; p = 0.012]. Respiratory modulation of lingual EMG occurred mainly during SWS and was similarly infrequent in both groups, and the incidence of sighs and central apneas also was similar. Thus, a weakened action of selected lingual muscles did not produce sleep-disordered breathing but resulted in a relatively elevated activity in other lingual muscles during SWS. These results encourage more extensive surgical manipulations with the aim to obtain a rodent model with collapsible upper airway.

International audience; Agamid lizards use tongue prehension for capturing all types of prey. The purpose of this study was to investigate the functional relationship between tongue structure, both surface and musculature, and function during prey capture in Pogona vitticeps. The lack of a detailed description of the distribution of fibre-types in the tongue muscles in some iguanian lizards has hindered the understanding of the functional morphology of the lizard tongue. Three methodological approaches were used to fill this gap. First, morphological analyses were performed (i) on the tongue surface through scanning electron microscopy, and (ii) on the lingual muscle by histological coloration and histochemistry to identify fibre-typing. Secondly, kinematics of prey capture was quantified by using high-speed video recordings to determine the movement capabilities of the tongue. Finally, electromyography (EMG) was used to identify the motor pattern tongue muscles during prey capture. Morphological and functional data were combined to discuss the functional morphology of the tongue in agamid lizards, in relation to their diet. During tongue protraction, M. genioglossus contracts 420 ± 96 ms before tongue-prey contact. Subsequently, Mm. verticalis and hyoglossus contract throughout tongue protraction and retraction. Significant differences are found between the timing of activity of the protractor muscles between omnivorous agamids (Pogona sp., this study) and insectivorous species (Agama sp.), despite similar tongue and jaw kinematics. The data confirm that specialisation toward a diet which includes more vegetal materials is associated with significant changes in tongue morphology and function. Histoenzymology demonstrates that protractor and retractor muscles differ in fibre composition. The proportion of fast glycolytic fibres is significantly higher in the M. hyoglossus (retractor muscle) than in the M. genioglossus (protractor muscle), and this difference is proposed to be associated with differences in the velocity of tongue protrusion and retraction (5 ± 5 and 40 ± 13 cm s(-1) , respectively), similar to Chamaeleonidae. This study provides a way to compare fibre-types and composition in all iguanian and scleroglossan lizards that use tongue prehension to catch prey.

1. Our purpose was to examine the effects of chemoreceptor stimulation and lung inflation on neural drive to tongue protrudor and retractor muscles in the rat. 2. Inspiratory flow, tidal volume, transpulmonary pressure, compliance and electromyographic (EMG) activity of genioglossus (GG), hyoglossus (HG) and inspiratory intercostal (IIC) muscles were studied in 11 anaesthetized, tracheotomized and spontaneously breathing rats. Mean EMG activity during inspiration was compared with mean EMG activity during an occluded inspiration, at each of five levels of inspired CO(2) (0, 3, 6, 9 and 12 %). 3. Lung inflation suppressed EMG activity in all muscles, with the effect on both tongue muscles exceeding that of the intercostal muscles. Static elevations of end-expiratory lung volume evoked by 2 cmH(2)O positive end-expiratory pressure (PEEP) had no effect on tongue muscle activity. 4. Despite increasing inspiratory flow, tidal volume and transpulmonary pressure, the inhibition of tongue muscle activity by lung inflation diminished as arterial PCO2 (P(a),CO(2)) increased. 5. The onset of tongue muscle activity relative to the onset of IIC muscle activity advanced with increases in P(a),CO(2) but was unaffected by lung inflation. This suggests that hypoglossal and external intercostal motoneuron pools are controlled by different circuits or have different sensitivities to CO(2), lung inflation and/or anaesthetic agents. 6. We conclude that hypoglossal motoneuronal activity is more strongly influenced by chemoreceptor-mediated facilitation than by lung volume-mediated inhibition. Hypoglossal motoneurons driving tongue protrudor and retractor muscles respond identically to these stimuli.

Repeated electrical or hypoxic stimulation of peripheral chemoreceptors has been shown to cause a persistent poststimulus increase in respiratory motoneuron activity, termed long-term facilitation (LTF). LTF after episodic hypoxia has been demonstrated most consistently in anesthetized, vagotomized, paralyzed, artificially ventilated rats. Evidence for LTF in spontaneously breathing animals and humans after episodic hypoxia is equivocal and may have been influenced by the awake state of the subjects in these studies. The present study was designed to test the hypothesis that LTF is evoked in respiratory-related tongue muscle and inspiratory pump muscle activities after episodic hypoxia in 10 spontaneously breathing, anesthetized, vagotomized rats. The animals were exposed to three (5-min) episodes of isocapnic hypoxia, separated by 5 min of hyperoxia (50% inspired oxygen). Genioglossus, hyoglossus, and inspiratory intercostal EMG activities, along with respiratory-related tongue movements and esophageal pressure, were recorded before, during, and for 60 min after the end of episodic isocapnic hypoxia. We found no evidence for LTF in tongue muscle (genioglossus, hyoglossus) or inspiratory pump muscle (inspiratory intercostal) activities after episodic hypoxia. Rather, the primary poststimulus effect of episodic hypoxia was diminished respiratory frequency, which contributed to a reduction in ventilatory drive.

This study was designed to investigate the influence of hypoxia-evoked augmented breaths (ABs) on respiratory-related tongue protrudor and retractor muscle activities and inspiratory pump muscle output. Genioglossus (GG) and hyoglossus (HG) electromyogram (EMG) activities and respiratory-related tongue movements were compared with peak esophageal pressure (Pes; negative change in pressure during inspiration) and minute Pes (Pes × respiratory frequency = Pes/min) before and after ABs evoked by sustained poikilocapnic, isocapnic, and hypercapnic hypoxia in spontaneously breathing, anesthetized rats. ABs evoked by poikilocapnic and isocapnic hypoxia triggered long-lasting (duration at least 10 respiratory cycles) reductions in GG and HG EMG activities and tongue movements relative to pre-AB levels, but Pes was reduced transiently (duration of 2 to the hypoxic inspirate had no effect on the frequency of evoked ABs, but this prevented long-term declines in tongue muscle activities. Bilateral vagotomy abolished hypoxia-induced ABs and stabilized drive to the tongue muscles during each hypoxic condition. We conclude that, in the rat, hypoxia-evoked ABs 1) elicit long-lasting reductions in protrudor and retractor tongue muscle activities, 2) produce short-term declines in inspiratory pump muscle output, and 3) are mediated by vagal afferents. The more prolonged reductions in pharyngeal airway vs. pump muscle activities may lead to upper airway narrowing or collapse after spontaneous ABs.

This anatomical investigation in the rat was designed to illustrate the detailed organization of the tongue's muscles and their innervation in order to elucidate the actions of the muscles of the higher mammalian tongue and thereby clarify the protrusor subdivision of the hypoglossal-tongue complex. The hypoglossal innervated, extrinsic styloglossus, hyoglossus, and genioglossus and the intrinsic transversus, verticalis and longitudinalis linguae muscles were observed by microdissection and analysis of serial transverse-sections of the tongue. Sihler's staining technique was applied to whole rat tongues to demonstrate the hypoglossal nerve branching patterns. Dissections of the tongue demonstrate the angles at which the extrinsic muscles act on the base of the tongue. The Sihler stained hypoglossal nerves demonstrate branches to the styloglossus and hyoglossus emanating from its lateral division while branches to the genioglossus muscle exit from its medial division. The largest portions of both XIIth nerve divisions can be seen to enter the body of the tongue to innervate the intrinsic muscles. Transverse sections of the tongue demonstrate the organization of the intrinsic muscle fibers of the tongue. Longitudinal muscle fibers run along the entire circumference of the tongue. Alternating sheets of transverse lingual and vertical lingual muscles can be observed to insert into the circumference of the tongue. Most importantly in clarifying tongue protrusion, we demonstrate the transversus muscle fibers enveloping the most superior and inferior portions of the longitudinalis muscles. Longitudinal muscle fascicles are completely encircled and thus are likely to be compressed by transverse muscle fascicles resulting in elongation of the tongue. We discuss our findings in relation to biomechanical studies, that describe the tongue as a muscular hydrostat and thereby define the "elongation-protrusion apparatus" of the mammalian tongue. In so doing, we clarify the functional organization of the hypoglossal-tongue complex.

"#$%!&$ The movements of the tongue, hyoid, and jaw were recorded cineradiographically in preweaning pigs as they suckled bariumized milk from a veterinary teat or drank it from a bowl. The movements were quantified by measuring the X, Y coordinates of radioopaque markers embedded in the tongue and attached to both jaws and to the hyoid. EMG activity in masseter, anterior digastric, geniohyoid, genioglossus, hyoglossus, sternohyoid, stylohyoid, and omohyoid muscles was recorded synchronously with cineradiography at 100 frames/sec. In both suckling and drinking, the movements were characterized by minimal movements of the jaw and hyoid but extensive movements of the tongue. In suckling, the movements were largely confined to the mid- posterior part of the tongue. A seal was formed between the posterior tongue and soft palate while a depression formed in the mid-tongue; this was associated with fluid moving into the depression probably because of a reduced intraoral pressure. The depression was associated with increased EMG activity in the genioglossus muscle and overlapping activity in digastric, geniohyoid, hyoglos- sus, and sternohyoid muscles. In drinking cycles, significant movement occurred in all parts of the tongue; milk ingestion was associated with tongue movements that combined elements character- istic both of suckling (mid-tongue depression with a posterior seal) and of lapping (extensive antero- posterior movements within the tongue itself). In drinking, compared to suckling, there was a major reduction in EMG activity in masseter, digastric, geniohyoid, and sternohyoid muscles. Af- ter milk had accumulated in the valleculae, swallows usually occurred in every other cycle during suckling and in every third or fourth cycle during drinking. The emptying of the valleculae was an event that was embedded in the early jaw-opening phase of an otherwise normal suckling or drinking cycle. Emptying of the valleculae was associated with posteriorly directed movement of the back of the tongue and increased EMG activity in hyoglossus, styloglossus, and omohyoid muscles. No differences were noted in the kinematics associated with swallowing in the two activi- ties, but, in the normalized and averaged EMG data, there were significant differences in the timing of genioglossus activity and in the relative balance of hyoglossal and stylohyoid activity. '( )*+(,-../(,01234 © 1998 Wiley-Liss, Inc.

Physiological articulatory models have evolved from simpler forms to complex ones, while recent models preserve traits of oversimplification and anatomical unreality. This work combines MRI observations at ATR-BAIC and Johns Hopkins University to point to the issue for advancing extrinsic tongue muscle modeling. The genioglossus, previously thought to arise from the genial tubercle of the mandible, has direct fiber attachments on the short tendon of the tongue. The posterior genioglossus, being regarded as a functional division of the muscle, can be given anatomical definition to the horizontal bundle arising from the inferior aspect of the short tendon. The styloglossus has been modeled as linear strings traveling 'free in air' before inserting into the tongue, but the extralingual part is actually restrained by the surrounding soft tissues to lack mobility. The intralingual styloglossus forms anterior and posterior slings in the tongue tissue, possibly with the distal fibers of the hyoglossus. Combined styloglossus and hyoglossus shortening via the slings may be a factor shaping the tongue into various forms.

The influence of lingual muscle activity on airflow dynamics in the upper airway was examined in nine patients with obstructive sleep apnea. Muscles that retract the tongue (hyoglossus and styloglossus) and protrude the tongue (genioglossus) were selectively stimulated electrically during sleep with fine wire electrodes placed intramuscularly transorally. We confirmed that stimulation with 50 Hz and 40-microseconds pulse duration did not elicit changes in electroencephalographic patterns or heart rate or alter airflow after the stimulation burst had ceased. The highest stimulus intensity that did not arouse patients from sleep was then utilized to examine the effect of lingual muscle recruitment on airflow dynamics during steady-state periods of inspiratory airflow limitation. When applying a stimulus burst during single inspirations, maximal inspiratory airflow decreased by 239 +/- 177 ml/s (P < 0.05) during retractor stimulation, whereas maximal inspiratory airflow increased by 217 +/- 93 ml/s during protrusor stimulation (P < 0.001) compared with breaths immediately before and after the stimulated breath. When consecutive inspirations were stimulated repeatedly, protrusor stimulation decreased the frequency of obstructive breathing episodes in four patients breathing at 3.9 +/- 3.4 (SD) cmH2O nasal pressure. The findings suggest that stimulation of the lingual muscles can increase or decrease airflow depending on the specific muscles stimulated without arousing patients from sleep.

The ability of a 2‐D biomechanical model of the tongue to reproduce kinematic properties of human tongue movements in V‐V transitions is assessed. The model consists of a finite elements description, and simulates the main agonist/antagonist muscle pairs (posterior Genioglossus/Hyoglossus and anterior Genioglossus/Styloglossus). The external geometrical shape of the model has been adapted from X‐ray data, to fit the tongue contours of a French native speaker. Movement data were collected on this speaker with an electromagnetometer (Carstens Electronics, AG100) for the tokens[i‐a], [i‐e], [i‐e], [a‐i], [e‐i], [e‐i], [i‐e‐e‐a], [a‐e‐e‐i], [y‐œ], [y‐o], [y‐u], [u‐y], [o‐y], [œ‐y], [y‐œ‐o‐u], [u‐o‐œ‐y]. For each token, the speaker was asked to keep the lip shape constant. The jaw was held in a constant position with a small bite‐block (5 mm). For the simulations, according to Feldman’s equilibrium‐point hypothesis [A. Feldman, ‘‘Once more Equilibrium‐Point Hypothesis for motor control,’’ J. Motor Behav. 18 (1...

The current T4a subclassification of the TNM staging system for oral malignancies has been criticised as based almost exclusively on anatomical data. The aim of this study was to provide anatomical confirmation of the muscular constraints of T4a classification of oral tongue tumours.A detailed anatomical study describing and measuring the adjacency of the named extrinsic tongue muscles to the lateral tongue surface was completed on the Visible Human Female (VHF). The distance of styloglossus and hyoglossus to the over lying mucosa were determined.The appearance, position, orientation and anatomical relationships of the lateral tongue extrinsic muscles, with comparison to their classical descriptions are described. The right VHF styloglossus was 1.3 mm (0.33-1.48) and left 2.91 mm (0.66-7.68) from the mucosal surface in the axial plane. The right VHF hyoglossus was 2.93 mm (1.48-4.96) and left 4.33 (1.68-8.71) from the mucosal surface in the axial line.In the lateral tongue, styloglossus and hyoglossus are very superficial. The inclusion criteria of hyoglossus and styloglossus in the T4a staging does not appear justified based upon their anatomical position.

The intrinsic lingual neural interconnections are overlooked. It was hypothesized that intralingual anatomically well defined anastomoses interconnect the somatic and autonomic neural systems of the tongue. It was thus aimed to evaluate the intralingual neural scaffold in human tongues. Human tongue samples (ten adult and one pediatric) were microdissected (4.5 magnification). In the interstitium between the genioglossus and hyoglossus muscles, the branches of the lingual nerve (LN) and the medial trunk of the hypoglossal nerve (HN) had a layered disposition of the outer and inner side, respectively, of the lingual artery with its periarterial plexus. Anastomoses of these three distinctive neural suppliers of tongue were recorded, as also were those of the LN with the lateral trunk of the HN and the anastomoses between successive terminal branches of the LN. Successive ansae linguales were joining the LN branches and the medial trunk of the HN. The intrinsic neural system of the tongue supports integrative functions and allows a better retrospective understanding of various experimental studies. The topographical pattern is useful for an accurate diagnosis of intralingual nerves on microscopic slides.

To demonstrate the relationship between lingual myoarchitecture and mechanics during swallowing, we performed a finite-element (FE) simulation of lingual deformation employing mesh aligned with the vector coordinates of myofiber tracts obtained by diffusion tensor imaging with tractography in humans. Material properties of individual elements were depicted in terms of Hill's three-component phenomenological model, assuming that the FE mesh was composed of anisotropic muscle and isotropic connective tissue. Moreover, the mechanical model accounted for elastic constraints by passive and active elements from the superior and inferior directions and the effect of out-of-plane muscles and connective tissue. Passive bolus effects were negligible. Myofiber tract activation was simulated over 500 ms in 1-ms steps following lingual tip association with the hard palate and incorporated specifically the accommodative and propulsive phases of the swallow. Examining the displacement field, active and passive muscle stress, elemental stretch, and strain rate relative to changes of global shape, we demonstrate that lingual reconfiguration during these swallow phases is characterized by (in sequence) the following: 1) lingual tip elevation and shortening in the anterior-posterior direction; 2) inferior displacement related to hyoglossus contraction at its inferior-most position; and 3) dominant clockwise rotation related to regional contraction of the genioglossus and contraction of the hyoglossus following anterior displacement. These simulations demonstrate that lingual deformation during the indicated phases of swallowing requires temporally patterned activation of intrinsic and extrinsic muscles and delineate a method to ascertain the mechanics of normal and pathological swallowing.

The tongue is an intricately configured muscular organ that undergoes a stereotypical set of deformations during the course of normal human swallowing. In order to demonstrate quantitatively the relationship between 3D aligned lingual fiber organization and mechanics during swallowing, the tissue's myoarchitecture and strain rate were imaged before and during the propulsive phase of a 3.0ml water bolus swallow. Mesoscale fiber organization was imaged with high-resolution diffusion tensor imaging (DTI) and multi-voxel myofiber tracts generated along maximum diffusion vectors. Tissue compression/expansion was obtained via lingual pressure-gated phase-contrast (PC) MRI, a method which determines local strain rate as a function of the phase shift occurring along an applied gradient vector. The co-alignment of myofiber tract direction and the localized principal strain rate vectors was obtained by translating the strain rate tensor into the reference frame with the primary axis parallel to the maximum diffusion vector using Mohr's circle, resulting in the generation of fiber-aligned strain rate (FASR). DTI tractography displayed the complete fiber anatomy of the tongue, consisting of a core region of orthogonally aligned fibers encased within a longitudinal sheath, which merge with the externally connected styloglossus, hyoglossus, and genioglossus fibers. FASR images obtained in the mid-sagittal plane demonstrated that bolus propulsion was associated with prominent compressive strain aligned with the genioglossus muscle combined with expansive strain aligned with the verticalis and geniohyoid muscles. These data demonstrate that lingual deformation during swallowing involves complex interactions involving intrinsic and extrinsic muscles, whose contractility is directed by the alignment of mesoscale fiber tracts.

This study was performed to assess the feasibility of investigating the complex lingual myoarchitecture through segmentation of muscles from diffusion tensor imaging (DTI) data. The primary eigenvectors were found to be adequate for delineating the superior and inferior longitudinalis, genioglossus, and hyoglossus. The tertiary eigenvector orientations effectively revealed the homogeneous and systematic change of muscle orientation in the tongue core. In the longitudinalis near the tongue tip, the secondary eigenvectors were oriented in the radial direction. Lingual muscles were segmented using two methods: modified directional correlation (DC) and tensor coherence (TC) methods. The DC method, based on one eigenvector, was found to be inadequate for lingual muscle segmentation, whereas the TC method, based on the tensor shape and orientation, was used successfully to segment most lingual muscles. The segmentation result was used to report the diffusion tensor properties of individual lingual muscles. Also found was a continuous change in skewness of the intrinsic tongue core from negative in the anterior region to positive in the posterior region. DTI and the proposed segmentation method provide an adequate means of imaging and visualizing the complex, compartmentalized musculature of the tongue. The potential for in vivo research and clinical applications is demonstrated.

Postnatal development of hyoglossus and styloglossus motoneurons was studied in this investigation of the hypoglossal nucleus. Our findings show separate and distinct locations for hyoglossus and styloglossus motoneurons within the retrusor (dorsal) subdivision of the hypoglossal nucleus for all age groups. Hyoglossus and styloglossus motoneuron cross-sectional area reached their adult size at different times (by weeks 2 and 3, respectively). Cell roundness, as measured by form factor (measure of cell perimeter relative to its area), decreased with advancing postnatal age for both populations of motoneurons. Differences in the direction of the dendritic projection between hyoglossus and styloglossus motoneurons were found. Hyoglossus and styloglossus motoneuron development was compared to genioglossus motoneuron postnatal development.

This study explores the following hypothesis: forward looping movements of the tongue that are observed in VCV sequences are due partly to the anatomical arrangement of the tongue muscles, how they are used to produce a velar closure, and how the tongue interacts with the palate during consonantal closure. The study uses an anatomically based two-dimensional biomechanical tongue model. Tissue elastic properties are accounted for in finite-element modeling, and movement is controlled by constant-rate control parameter shifts. Tongue raising and lowering movements are produced by the model mainly with the combined actions of the genioglossus, styloglossus, and hyoglossus. Simulations of V1CV2 movements were made, where C is a velar consonant and V is [a], [i], or [u]. Both vowels and consonants are specified in terms of targets, but for the consonant the target is virtual, and cannot be reached because it is beyond the surface of the palate. If V1 is the vowel [a] or [u], the resulting trajectory describes a movement that begins to loop forward before consonant closure and continues to slide along the palate during the closure. This pattern is very stable when moderate changes are made to the specification of the target consonant location and agrees with data published in the literature. If V1 is the vowel [i], looping patterns are also observed, but their orientation was quite sensitive to small changes in the location of the consonant target. These findings also agree with patterns of variability observed in measurements from human speakers, but they contradict data published by Houde [Ph.D. dissertation (1967)]. These observations support the idea that the biomechanical properties of the tongue could be the main factor responsible for the forward loops when V1 is a back vowel, regardless of whether V2 is a back vowel or a front vowel. In the [i] context it seems that additional factors have to be taken into consideration in order to explain the observations made on some speakers.

To help understanding tongue shape and motions, a physical figure model of tongue muscles using viscoelastic material of urethane rubber gel were made by improving previous models. Compare to previous shape tongue models that had been made and presented, the new model is constructed from tongue body (consisting of Transversus linguae, Verticalis linguae, Longitudinalis linguae superior, and Longitudinalis linguae inferior), and individual extrinsic tongue muscles (consisting of Genioglossus anterior, Genio glossus posterior, Hyoglossus, Styloglossus, and Palatoglossus) parts. Therefore, each muscle’s shape, starting and ending points, and relation to other muscles and organs inside mouth are more understandable than previous ones. As the model is made from viscoelastic material similar to human skin, reshaping and moving tongue are possible by pulling or pushing some parts of the tongue muscle by hand, that is, tongue shape and motion simulations by hand can be done. The proposed model is useful for speech science education or a future speaking robot using realistic speech mechanism.

Whether electrical microstimulation of a rat’s striatal jaw region (SJR) in fact induced tongue or facial muscle activity in addition to jaw muscle activity was tested. Microstimulation of SJR-evoked EMG activity in a jaw-opener (anterior digastricus) and tongue-protruder (genioglossus). No activity was evoked in jaw-closers (temporalis or masseter), tongue-retractor (hyoglossus) or in facial muscles. In addition, the EMG effect could still be induced after extensive ablation of the neocortex; it was reproduced by microinjection of 50 mM kainic acid into SJR. The effective sites were histologically localized to a small central striatal region adjoining the anterior commissure. These findings may be of considerable value in understanding the striatal mechanism of orolingual dyskinesia involving involuntary jaw and tongue movements.

The influence of systemic hypoxia on the endurance performance of tongue protrudor and retractor muscles was examined in anesthetized, ventilated rats. Tongue protrudor (genioglossus) or retractor (hyoglossus and styloglossus) muscles were activated via medial or lateral XII nerve branch stimulation (0.1-ms pulse; 40 Hz; 330-ms trains; 1 train/s). Maximal evoked potentials (M waves) of genioglossus and hyoglossus were monitored with electromyography. Fatigue tests were performed under normoxic and hypoxic (arterial[Formula: see text] = 50 ± 1 Torr) conditions in separate animals. The fatigue index (FI; %initial force) after 5 min of normoxic stimulation was 85 ± 6 and 79 ± 7% for tongue protrudor and retractor muscles, respectively; these values were significantly lower during hypoxia (protrudor FI = 52 ± 10, retractor FI = 18 ± 6%; P < 0.05). Protrudor and retractor muscle M-wave amplitude declined over the course of the hypoxic fatigue test but did not change during normoxia ( P < 0.05). We conclude that hypoxia attenuates tongue protrudor and retractor muscle endurance performance; potential mechanisms include neuromuscular transmission failure and/or diminished sarcolemmal excitability.

The tongue manipulates food while chewing and swallowing, dilates the airway during inspiration, and shapes the sounds of speech in humans. While performing these functions the tongue morphs through many complex shapes. At present it is not known how the muscles of the tongue perform these complex shape changes. The difficulty in understanding tongue biomechanics is partly due to gaps in our knowledge regarding the complex neuromuscular anatomy of the tongue. In this study the motor and sensory nerve anatomy of four canine tongues was studied with Sihler's stain, a technique that renders most of the tongue tissue translucent while counterstaining nerves. An additional tongue specimen was serially sectioned to provide a reference for the muscle structure of the tongue. The hypoglossal nerve (XII) has approximately 50 primary nerve branches that innervate all intrinsic and extrinsic tongue muscles. Two extrinsic muscles, the styloglossus and hyoglossus, are innervated by about three to four branches from the lateral division of the XII. The third extrinsic muscle, the genioglossus, is composed of oblique and horizontal compartments, which receive about ten nerve branches from the medial division of the XII. The intrinsic muscles are composed of many neuromuscular compartments. On each side, the superior longitudinal muscle had an average of 40 distinct muscle fascicles that spanned the length of the tongue. Each of the fascicles is supplied by a nerve branch. The inferior longitudinal muscle had a similar organization. Each of the transverse and vertical muscles is composed of over 140 separate muscle sheets, and every sheet is innervated by a separate terminal nerve. The muscle sheets from the vertical and transverse alternate their orientation 90 degrees throughout the length of the tongue. It is concluded that the intrinsic canine tongue muscles are actually composed of groups of neuromuscular compartments that are arranged in parallel (longitudinal muscles) or in a precise alternating sequence (transverse and vertical muscles). This arrangement suggests that the compartments from the different tongue muscles could cooperate to control the three-dimensional contractile state of their local area. This hypothesis could explain how many different tongue shapes are formed, and is supported by physiologic evidence.

1. The purpose of these experiments was to examine the mechanisms by which either co-activation or independent activation of tongue protrudor and retractor muscles influence upper airway flow mechanics. We studied the influence of selective hypoglossal (XIIth) nerve stimulation on tongue movements and flow mechanics in anaesthetized rats that were prepared with an isolated upper airway. In this preparation, both nasal and oral flow pathways are available. 2. Inspiratory flow limitation was achieved by rapidly lowering hypopharyngeal pressure (Php) with a vacuum pump, and the maximal rate of flow (VI,max) and the nasopharyngeal pressure associated with flow limitation (Pcrit) were measured. These experimental trials were repeated while nerve branches innervating tongue protrudor (genioglossus; medial XIIth nerve branch) and retractor (hyoglossus and styloglossus; lateral XIIth nerve branch) muscles were stimulated either simultaneously or independently at frequencies ranging from 20-100 Hz. Co-activating the protrudor and retractor muscles produced tongue retraction, whereas independently activating the genioglossus resulted in tongue protrusion. 3. Co-activation of tongue protrudor and retractor muscles increased VI, max (peak increase 44 %, P < 0.05), made Pcrit more negative (peak decrease of 44 %, P < 0.05), and did not change upstream nasopharyngeal resistance (Rn). Independent protrudor muscle stimulation increased VI,max (peak increase 61 %, P < 0.05), did not change Pcrit, and decreased Rn (peak decrease of 41 %, P < 0.05). Independent retractor muscle stimulation did not significantly alter flow mechanics. Changes in Pcrit and VI,max at all stimulation frequencies were significantly correlated during co-activation of protrudor and retractor muscles (r2 = 0.63, P < 0.05), but not during independent protrudor muscle stimulation (r2 = 0.09). 4. These findings indicate that either co-activation of protrudor and retractor muscles or independent activation of protrudor muscles can improve upper airway flow mechanics, although the underlying mechanisms are different. We suggest that co-activation decreases pharyngeal collapsibility but does not dilate the pharyngeal airway. In contrast, unopposed tongue protrusion dilates the oropharynx, but has a minimal effect on pharyngeal airway collapsibility.