Intrinsic Tongue Muscles Research Articles

Anatomic Invasive Depth Predicts Delayed Cervical Lymph Node Metastasis of Tongue Squamous Cell Carcinoma.

Delayed cervical lymph node metastasis (CLNM) is the most negative prognostic factor of tongue squamous cell carcinoma (SCC). This study analyzed the relationship between clinicopathologic factors, including anatomic invasive depth (AID), and CLNM. A total of 212 patients with clinically node-negative (cN0) tongue SCC who had undergone partial glossectomy through the mouth were eligible for this retrospective study. The deepest portions where tongue SCC cells invaded as determined by microscopic analyses were classified into 5 categories, including epithelial and submucosal tissue, lateral extrinsic tongue muscle (ETM), intrinsic tongue muscles (ITM), paralingual and sublingual spaces, and medial ETM according to AID. We examined the relationship between clinicopathologic factors including AID and delayed CLNM. Multivariate analysis demonstrated that AID was an independent predictive factor for delayed CLNM (P=0.0022; odds ratio=7.1). Deeper invasion than ITM, including ITM, paralingual and sublingual spaces, and medial ETM, had high sensitivity and negative predictive value for delayed CLNM (94.4% and 95.7%, respectively). Precise elucidation of AID may be useful for the preoperative decision for performing elective neck dissection. None of 11 patients in whom the deepest portion where tumor invaded to lateral ETM (according to AID) showed delayed CLNM, although tongue SCC T4a tumor is defined by the presence of invasion of cancer cells to ETM. Tumors with invasion to lateral ETM might have to be excluded from the pathologic T4a category.

Beyond mean pharyngeal constrictor dose for beam path toxicity in non-target swallowing muscles: Dose–volume correlates of chronic radiation-associated dysphagia (RAD) after oropharyngeal intensity modulated radiotherapy

Purpose/objective(s)We sought to identify swallowing muscle dose–response thresholds associated with chronic radiation-associated dysphagia (RAD) after IMRT for oropharyngeal cancer. Materials/methodsT1–4 N0–3 M0 oropharyngeal cancer patients who received definitive IMRT and systemic therapy were examined. Chronic RAD was coded as any of the following ⩾12months post-IMRT: videofluoroscopy/endoscopy detected aspiration or stricture, gastrostomy tube and/or aspiration pneumonia. DICOM-RT plan data were autosegmented using a custom region-of-interest (ROI) library and included inferior, middle and superior constrictors (IPC, MPC, and SPC), medial and lateral pterygoids (MPM, LPM), anterior and posterior digastrics (ADM, PDM), intrinsic tongue muscles (ITM), mylo/geniohyoid complex (MHM), genioglossus (GGM), masseter (MM), buccinator (BM), palatoglossus (PGM), and cricopharyngeus (CPM), with ROI dose–volume histograms (DVHs) calculated. Recursive partitioning analysis (RPA) was used to identify dose–volume effects associated with chronic-RAD, for use in a multivariate (MV) model. ResultsOf 300 patients, 34 (11%) had chronic-RAD. RPA showed DVH-derived MHM V69 (i.e. the volume receiving⩾69Gy), GGM V35, ADM V60, MPC V49, and SPC V70 were associated with chronic-RAD. A model including age in addition to MHM V69 as continuous variables was optimal among tested MV models (AUC 0.835). ConclusionIn addition to SPCs, dose to MHM should be monitored and constrained, especially in older patients (>62-years), when feasible.

Tongue electrical impedance in amyotrophic lateral sclerosis modeled using the finite element method

ObjectiveElectrical impedance myography (EIM) of the tongue has demonstrated alterations in patients with amyotrophic lateral sclerosis (ALS) compared to normal subjects. Whether these differences are due to reduced tongue size or diseased-associated alterations in the electrical characteristics of intrinsic tongue muscles is uncertain. MethodsWe employed computer simulations using the finite element method, inputting data from healthy and ALS mouse muscle, to help answer that question, comparing our modeled results to human data. ResultsThe models revealed that much of the electrical current flows superficially in the tongue and that tongue thickness only begins to have a major impact on the measured impedance when substantial atrophy is present. Modeled values paralleled the human tongue data. ConclusionsThese findings suggest that the observed changes in tongue impedance in ALS are mainly due to alterations in the electrical properties of the tongue and are not a mere consequence of tongue volume loss. SignificanceFurther development of EIM for evaluation of bulbar dysfunction in ALS may provide useful information on drug efficacy and could serve as a biomarker in future clinical trials.

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Journal of Paediatrics and Child HealthVolume 50, Issue 11 p. 935-935 Letter to the EditorFree Access Answers First published: 06 November 2014 https://doi.org/10.1111/jpc.12563_2AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Left hypoglossal nerve (cranial nerve XII) palsy Isolated unilateral tongue weakness, in general, implies damage at the level of the hypoglossal nucleus or hypoglossal nerve, rather than a lesion in the cerebral hemisphere. Weakness of the intrinsic tongue muscles allows the contralateral muscles to ‘push’ the tongue towards the side of the lesion. This also applies to the jaw deviation seen with trigeminal (cranial nerve V) nerve palsy, where the weak side is pushed by the contralateral stronger pterygoids, resulting in deviation ipsilateral to the nerve palsy. This is in contrast to the deviation of the angle of mouth seen in facial (cranial nerve VII) and of the uvula seen in vagal (cranial nerve X) nerve palsies, which both deviate contralateral to the side of the pathology. This is well remembered by a mneumonic – Rule of 17 (12 + 5 = 10 + 7). Magnetic resonance imaging brain Hypoglossal nerve palsy is an ominous sign with about 50% patients having an underlying intra- or extra-cranial malignancy.1 It has also been described with varied aetiologies including gunshot wound to the neck, blunt head trauma, stroke, multiple sclerosis, internal carotid artery aneurysm, and post-infectious and post-vaccination neuropathy.2 Surgical trauma due to branchial cyst removal Magnetic resonance imaging of the brain was done and was unremarkable. Hypoglossal nerve palsy resulting from infected neck cysts or its surgical removal has been reported.3, 4 Malformations arising from the second or third branchial cleft remnants are in anatomic proximity to the hypoglossal nerve, making it prone to surgical trauma. The chances of recovery in these cases are low, although patients may continue to be ‘asymptomatic’ as was our patient. References 1Keane JR. Twelfth-nerve palsy. Analysis of 100 cases. Arch. Neurol. 1996; 53: 561– 566. CrossrefCASPubMedWeb of Science®Google Scholar 2Combarros O, Alvarez de Arcaya A, Berciano J. Isolated unilateral hypoglossal nerve palsy: nine cases. J. Neurol. 1998; 245: 98– 100. CrossrefCASPubMedWeb of Science®Google Scholar 3Gatot A, Tovi F, Fliss DM, Yanai-Inbar I. Branchial cleft cyst manifesting as hypoglossal nerve palsy. Head Neck 1991; 13: 249– 250. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar 4Mukherjee SK, Gowshami CB, Salam A, Kuddus R, Farazi MA, Baksh J. A case with unilateral hypoglossal nerve injury in branchial cyst surgery. J. Brachial Plex. Peripher. Nerve Inj. 2012; 7: 2. CrossrefPubMedGoogle Scholar Volume50, Issue11November 2014Pages 935-935 ReferencesRelatedInformation

Nerve terminal distribution in the human tongue intrinsic muscles: An immunohistochemical study using midterm fetuses

Intrinsic tongue muscles, especially the transverse and vertical (T&V) muscles, regulate the shape of the tongue. However, little information is available on the nerve distribution pattern in human T&V muscles. Using S100 protein immunohistochemistry for paraffin-embedded histology, we investigated semiserial sagittal or frontal sections of eight human fetal tongues (180-240 mm crown-rump length: CRL). The height of the T&V muscle bundle showed a threefold difference between specimens with a small and a large CRL. Thus, the T&V muscles were still growing at the stages examined. In the intrinsic longitudinal muscles and all extrinsic tongue muscles, we observed the typical motor endplate band. In lower-magnification views, the T&V muscles also appeared to carry the band in the lateral part of the tongue, where the genioglossus muscle fibers did not cross these muscles. However, in higher magnification views, the nerve terminal distribution in the T&V muscles showed a unique rule: the nerve terminal for the transverse muscle bundle was located distantly from that of the adjacent vertical muscle bundle. This pattern seemed to be established during the stages examined. To provide such "distantly separated nerve terminals," thin nerve twigs took a highly curved course oblique to the T&V muscle bundles. We hypothesize that the unique nerve course and terminal distribution in the T&V muscles are a result of sorting to provide a good functional match between the nerve fiber and the muscle bundle. After sorting, the T&V muscle cells may initiate proliferation to increase the muscle bundle.

Origin, Course and Distribution of the Hypoglossal Nerve in the New Zealand Rabbit (Oryctolagus cuniculus L)

With 8 figures 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.

Proton magnetic resonance spectroscopy of the intrinsic tongue muscles in patients with myasthenia gravis with different autoantibodies

Objective To assess lipid composition of the intrinsic tongue muscles in patients with myasthenia gravis (MG). Methods This study included 15 MG patients with antibodies against muscle-specific kinase (MuSK), 15 matched MG patients with antibodies against acetylcholine receptor (AChR) and 15 matched healthy subjects. Middle posterior region of the tongue was analyzed by single voxel point-resolved proton magnetic resonance spectroscopy (MRS) using 1.5 T MRI scanner. Results MRS obtained from subject with AChR MG showed a broad resonance arising from methylene groups of lipids (PMN) with no observable shoulder attributed to methyl groups (PML). Full-width at half maximum (FWHM) of PMN + PML peak showed higher value in patients with AChR MG in comparison to healthy subjects and MuSK MG patients (p < 0.05). In patients with MuSK MG, the shape and FWHM of PMN + PML peak was similar as in healthy subjects (p > 0.05), with tendency toward increased ratio between PMN and resonance from vinyl protons of lipids (PV). In both AChR and MuSK MG, total creatine resonance (creatine + phosphocreatine, CP) was almost absent with significant increase of PMN/CP ratio in comparison to healthy subjects (p < 0.05). Conclusion MRS is useful in revealing muscle lipid composition in MG. In patients with AChR MG, MRS showed increased lipid content in the tongue muscles due to the lipid migration from intra- to extramyocellular space. Finding in patients with MuSK MG might reflect intramyocellular lipid deposition in the tongue. CP decrease in tongue muscles indicated impairment of oxidative metabolism in both AChR MG and MuSK MG.

Capillary Supply in Relation to Myosin Heavy Chain Fibre Composition of Human Intrinsic Tongue Muscles

The capillary supply and myosin heavy chain (MyHC) composition of three different intrinsic tongue muscles was analysed in the anterior and posterior regions of the human tongue with biochemical and immunohistochemical techniques. Mean capillary density for the whole tongue was 796 ± 82 cap/mm², without regional differences. The overall number of capillaries around each fibre (CAF) was higher in the posterior than in the anterior region (2.5 vs. 2.1, p = 0.009). However, correcting for regional differences in fibre size, CAF per fibre area was higher in the anterior region (4.3 vs. 3.0, p < 0.001). Muscle fibres containing fast MyHCs predominated in the anterior region (78.7%), consisting of MyHCIIa (58.5%), MyHCIIx (1.0%), MyHCIIa+MyHCIIx (11.3%) and MyHCI+MyHCIIa (7.9%). Fibres containing slow MyHC predominated in the posterior region (65.2%), consisting of MyHCI (45.5%) and MyHCI+MyHCIIa (19.7%). A minor fibre population (<2%) contained unusual MyHC isoforms, namely MyHC foetal, MyHC slow-tonic, MyHC α-cardiac or MyHC embryonic. The microvascularization of the human tongue was twice as high as in human limb muscles. Regional similarities in capillary supply, but differences in fibre phenotype composition, suggest that human tongue muscle fibres are fatigue resistant independently of MyHC content. High frequency of hybrid fibres, that is fibres co-expressing two or more MyHC isoforms, indicates a wider spectrum of fibre contractile properties than in limb muscles. In conclusion, human intrinsic tongue muscles showed internal specialization in distribution of MyHC isoforms and capillary supply, but not in the expression of unusual MyHCs.

Long-term impact of tongue reduction on speech intelligibility, articulation and oromyofunctional behaviour in a child with Beckwith–Wiedemann syndrome

The purpose of the present case study was to determine the long-term impact of partial glossectomy (using the keyhole technique) on overall speech intelligibility and articulation in a Dutch-speaking child with Beckwith–Wiedemann syndrome (BWS). Furthermore the present study is meant as a contribution to the further delineation of the phonation, resonance, articulation and language characteristics and oral behaviour in a child with BWS. Detailed information on the speech and language characteristics of children with BWS may lead to better guidance of pediatric management programs. The child's speech was assessed 9 years after partial glossectomy with regard to ENT characteristics, overall intelligibility (perceptual consensus evaluation), articulation (phonetic and phonological errors), voice (videostroboscopy, vocal quality), resonance (perceptual, nasometric assessment), language (expressive and receptive) and oral behaviour. A class III malocclusion, an anterior open bite, diastema, overangulation of lower incisors and an enlarged but normal symmetric shaped tongue were present. The overall speech intelligibility improved from severely impaired (presurgical) to slightly impaired (5 months post-glossectomy) to normal (9 years postoperative). Comparative phonetic inventory showed a remarkable improvement of articulation. Nine years post-glossectomy three types of distortions seemed to predominate: a rhotacism and sigmatism and the substitution of the alveolar /z/. Oral behaviour, vocal characteristics and resonance were normal, but problems with expressive syntactic abilities were present. The long-term impact of partial glossectomy, using the keyhole technique (preserving the vascularity and the nervous input of the remaining intrinsic tongue muscles), on speech intelligibility, articulation, and oral behaviour in this Dutch-speaking child with congenital macroglossia can be regarded as successful. It is not clear how these expressive syntactical problems demonstrated in this child can be explained. Certainly they are not part of a more general developmental delay, hearing problems or cognitive malfunctioning. To what extent the presence of expressive syntactical problems is a possible aspect of the phenotypic spectrum of children with BWS is subject for further research. Multiple variables, both known and unknown can affect the long-term outcome after partial glossectomy in a child with BWS. The timing and type of the surgical technique, hearing and cognitive functioning are known variables in this study. But variables such as children's motivation, the contribution of the motor-oriented speech therapy, the parental articulation input and stimulation and other family, school and community factors are unknown and are all factors which can influence speech outcome after partial glossectomy. Detailed analyses in a greater number of subjects with BWS may help further illustrate the long-term impact of partial glossectomy.

Genioglossus and Intrinsic Electromyographic Activities in Impeded and Unimpeded Protrusion Tasks

Eight muscles invest the human tongue: four extrinsic muscles have external origins and insert into the tongue body and four intrinsic muscles originate and terminate within the tongue. Previously, we noted minimal activation of the genioglossus tongue muscle during impeded protrusion tasks (i.e., having subjects push the tongue against a force transducer), suggesting that other muscles play a role in the production of tongue force. Accordingly, we sought to characterize genioglossus tongue muscle activities during impeded and unimpeded protrusion tasks (i.e., having subjects slowly and smoothly move the tongue out of their mouth). Electromyographic (EMG) and single motor-unit potentials of the extrinsic genioglossus muscle were recorded with tungsten microelectrodes and EMG activities of intrinsic tongue muscles were recorded with hook-wire electrodes inserted into the anterior tongue body. Tongue position was detected by an isotonic transducer coupled to the tongue tip. Protrusive force was detected by a force transducer attached to a rigid bar. Genioglossus and intrinsic tongue muscles were simultaneously active in both impeded and unimpeded protrusion tasks. Genioglossus whole muscle EMG and single motor-unit activities changed faithfully as a function of tongue position, with increased discharge associated with protrusion and decreased discharge associated with retraction back to the rest position. In contrast, during the impeded protrusion task drive the genioglossus muscle remained constant as protrusion force increased. Conversely, intrinsic tongue muscle activities appropriately followed changes in both tongue position and force. Importantly, we observed significantly higher levels of intrinsic muscle activity in the impeded protrusion task. These observations suggest that protrusion of the human tongue requires activation of the genioglossus and intrinsic protrudor muscles, with the former more important for establishing anterior-posterior tongue location and the latter playing a greater role in the generation of protrusive force. A biomechanical model of these actions is provided and discussed.

Quantitative Contributions of the Muscles of the Tongue, Floor-of-Mouth, Jaw, and Velum to Tongue-to-Palate Pressure Generation

The purpose of this investigation was to evaluate the relationship between tongue-to-palate pressure and the electromyography (EMG) measured from the mylohyoid, anterior belly of the digastric, geniohyoid, medial pterygoid, velum, genioglossus, and intrinsic tongue muscles. Methods Seven healthy adults performed tongue-to-palate pressure tasks at known percentages of their maximum pressure while intramuscular EMG was recorded from the muscles stated above. Multiple regression analysis was performed. Predictors of pressure included the posterior fibers of the genioglossus, mylohyoid, anterior belly of digastric, medial pterygoid, and intrinsic tongue. Increasing tongue-to-palate pressure coincides with increased muscle activity. Activation of the floor-of-mouth, tongue, and jaw closing muscles increased tongue-to-palate pressure. These findings support the use of a tongue-press exercise to strengthen floor-of-mouth muscles, tongue, and jaw-closing muscles.

FEM simulation of tongue deformation for /i/ with a four‐cube model applied to tagged cine‐MRI data

Roles of extrinsic and intrinsic tongue muscles in the production of vowel /i/ were examined using a finite element method (FEM) applied to the tagged cine‐MRI data. It has been thought that tongue tissue deformation for /i/ is mainly due to the combined actions of the genioglossus muscle bundles advancing the tongue root to elevate the dorsum with a mid‐line grooving. A recent study with the tagging‐MRI revealed earlier, faster and greater tissue deformation at anterior top of the tongue than posterior part during /ei/ production. This result implies the contribution of the intrinsic tongue muscle (transverse anterior) with an independent hydrostat mechanism from that of the genioglossus muscle bundles. In this study, a simple four‐cube model is built to examine the co‐contraction effect of the genioglossus and transverse muscles using using the FEM. The simulation result with the anterior transverse muscle (Ta) showed good agreement with the pattern of the tongue deformation obtained from the tagged‐MRI...

Roles of intrinsic and extrinsic tongue muscles in feeding: Electromyographic study in pigs

The performance of tongue muscles in various feeding behaviours is not well defined. This study was undertaken to examine the role of the intrinsic and extrinsic tongue muscles during natural drinking, food ingestion and chewing. Ten 12-week-old Yucatan miniature pigs (5 in each gender) were used. Under anesthesia, fine-wire electrodes were inserted into three intrinsic (verticalis and transversus [V/T]; superior and inferior longitudinalis [SL and IL]) and two extrinsic (genioglossus [GG] and styloglossus [SG]) tongue muscles and two jaw muscles (masseter [MA] and anterior digastricus [DI]). Electromyogram (EMG) and jaw movement were recorded and synchronized when pigs were drinking water, ingesting and chewing food freely. Chewing frequency (CF), onset of activation, burst duration and integrated activity (IEMG) were assessed quantitatively, and EMG activities during drinking and ingestion were examined qualitatively. Results indicate that during chewing, the V/T and GG had one phase of activity starting at early jaw opening, and the V/T activity lasted through late of jaw closing. The SL, IL and SG had double phases with the first starting at jaw opening and the second at late jaw closing phases. The three intrinsic tongue muscles and the SG were active during 35–48% of the chewing cycle. IEMG values of the SL, IL and SG of both sides were significantly greater compared to the other muscles ( p < 0.05–0.01). Both the SL and the IL showed significantly higher activities in the contralateral than ipsilateral sides ( p < 0.05). The timing sequences of both extrinsic and intrinsic muscles were similar between ingestion and chewing, but amplitudes of the GG and IL were greatly enhanced and those of the MA and SL were reduced during ingestion. The simultaneous activation of the MA, GG and V/T were seen during drinking, along with major activity in the GG and V/T. These results suggested that the majority of activity in the intrinsic and extrinsic tongue muscles occurred during jaw opening and the occlusal phases of chewing. The activity of the GG and IL played a major role during ingestion, whereas simultaneous activation of jaw, extrinsic and intrinsic tongue muscles and major activity in the GG and V/T occurred during drinking.

Tongue deformation, jaw movement and muscle activity during mastication in pigs

This study was undertaken to address the lack of information about tongue functional deformation in relation to jaw movement and muscle activity. Dimensional changes in tongue anterior and base widths, body length and base thickness were measured using six ultrasonic crystals implanted into the tongue in eight Yucatan minipigs. Jaw movements were captured on videotape and digitized, and electromyography (EMG) of tongue intrinsic (verticalis/transversus [V/T], superior and inferior longitudinalis [SL, IL]), extrinsic (genioglossus and styloglossus [GG, SG) and jaw (masseter and digastricus [MA, DI]) muscles were recorded. Signals from these three sources were synchronized. Tongue dimensions showed stereotyped and rhythmic changes during chewing cycles, with the largest changes in the body length and base thickness of the contralateral (non-working) side. The anterior tongue widened during jaw opening while the tongue base widened and thickened during jaw closing. The body lengthening accompanied base widening and ended at early power stroke, while base thickening lasted through most of the power stroke. Significant associations were found between changes of anterior width, body length and base thickness and integrated EMGs of VT, SL, SG, GG, MA and DI, but not IL. Thus, majority of tongue dimensional expansions occur during jaw closing. Intrinsic tongue muscle activities are not correlated more with tongue dimensional changes than are extrinsic tongue and jaw muscle activities.

Anatomic consequences of intrinsic tongue muscle activation

We recently showed respiratory-related coactivation of both extrinsic and intrinsic tongue muscles in the rat. Here, we test the hypothesis that intrinsic tongue muscles contribute importantly to changes in velopharyngeal airway volume. Spontaneously breathing anesthetized rats were placed in a MRI scanner. A catheter was placed in the hypopharynx and connected to a pressure source. Axial and sagittal images of the velopharyngeal airway were obtained, and the volume of each image was computed at airway pressures ranging from +5.0 to -5.0 cm H2O. We obtained images in the hypoglossal intact animal (i.e., coactivation of intrinsic and extrinsic tongue muscles) and after selective denervation of the intrinsic tongue muscles, with and without electrical stimulation. Denervation of the intrinsic tongue muscles reduced velopharyngeal airway volume at atmospheric and positive airway pressures. Electrical stimulation of the intact hypoglossal nerve increased velopharyngeal airway volume; however, when stimulation was repeated after selective denervation of the intrinsic tongue muscles, the increase in velopharyngeal airway volume was significantly attenuated. These findings support our working hypothesis that intrinsic tongue muscles play a critical role in modulating upper airway patency.

Normal Uptake of F-18 FDG in the Sublingual Gland

A symmetric inverted “V” pattern of high uptake in the floor of the mouth is a consistent normal finding on F-18 FDG PET. There is no general agreement on the nature of this highly FDG-avid structure. Mylohyoid muscle, insertion site of the genioglossus muscle, other intrinsic tongue muscles, and the sublingual gland have been suggested. I-123 SPECT and F-18 FDG PET scans were performed on the same day in a patient with papillary thyroid carcinoma. Both the I-123 SPECT and F-18 FDG PET showed the same inverted “V” pattern in the floor of the mouth, corresponding to the sublingual gland typically seen on magnetic resonance imaging.

PO2-dependent Changes in Intrinsic and Extrinsic Tongue Muscle Activities in the Rat

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. 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. 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 (Pa(O2), 160 +/- 12 mm Hg) and in mild isocapnic hypoxia (Pa(O2), 69 +/- 7.2 mm Hg), with and without brief (3-breath) airway occlusions, pre- and postbilateral vagotomy. (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. 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.

Pharyngeal airway wall mechanics using tagged magnetic resonance imaging during medial hypoglossal nerve stimulation in rats

To better understand pharyngeal airway mechanics as it relates to the pathogenesis and treatment of obstructive sleep apnoea, we have developed a novel application of magnetic resonance imaging (MRI) with non-invasive tissue tagging to measure pharyngeal wall tissue motion during active dilatation of the airway. Eleven anaesthetized Sprague-Dawley rats were surgically prepared with platinum electrodes for bilateral stimulation of the medial branch of the hypoglossus nerve that supplies motor output to the protrudor and intrinsic tongue muscles. Images of the pharyngeal airway were acquired before and during stimulation using a gated multislice, spoiled gradient recalled (SPGR) imaging protocol in a 4.7 T magnet. The tag pulses, applied before stimulation, created a grid pattern of magnetically imbedded dark lines that revealed tissue motion in images acquired during stimulation. Stimulation significantly increased cross-sectional area, and anteroposterior and lateral dimensions in the oropharyngeal and velopharyngeal airways when results were averaged across the rostral, mid- and caudal pharynx (P < 0.001). Customized software for tissue motion-tracking and finite element-analysis showed that changes in airway size were associated with ventral displacement of tissues in the ventral pharyngeal wall in the rostral, mid- and caudal pharyngeal regions (P < 0.0032) and ventral displacement of the lateral walls in the mid- and caudal regions (P < 0.0001). In addition, principal maximum stretch was significantly increased in the lateral walls (P < 0.023) in a ventral-lateral direction in the mid- and caudal pharyngeal regions and principal maximum compression (perpendicular to stretch) was significantly increased in the ventral walls in all regions (P < 0.0001). Stimulation did not cause lateral displacement of the lateral pharyngeal walls at any level. The results reveal that the increase in pharyngeal airway size resulting from stimulation of the medial branch of the hypoglossal nerve is predominantly due to ventral displacement of the ventral and lateral pharyngeal walls.

Coordination of intrinsic and extrinsic tongue muscles during spontaneous breathing in the rat

The muscular-hydrostat model of tongue function proposes a constant interaction of extrinsic (external bony attachment, insertion into base of tongue) and intrinsic (origin and insertion within the tongue) tongue muscles in all tongue movements (Kier WM and Smith KK. Zool J Linn Soc 83: 207-324, 1985). Yet, research that examines the respiratory-related effects of tongue function in mammals continues to focus almost exclusively on the respiratory control and function of the extrinsic tongue protrusor muscle, the genioglossus muscle. The respiratory control and function of the intrinsic tongue muscles are unknown. Our purpose was to determine whether intrinsic tongue muscles have a respiration-related activity pattern and whether intrinsic tongue muscles are coactivated with extrinsic tongue muscles in response to respiratory-related sensory stimuli. Esophageal pressure and electromyographic (EMG) activity of an extrinsic tongue muscle (hyoglossus), an intrinsic tongue muscle (superior longitudinal), and an external intercostal muscle were studied in anesthetized, tracheotomized, spontaneously breathing rats. Mean inspiratory EMG activity was compared at five levels of inspired CO2. Intrinsic tongue muscles were often quiescent during eupnea but active during hypercapnia, whereas extrinsic tongue muscles were active in both eupnea and hypercapnia. During hypercapnia, the activities of the airway muscles were largely coincident, although the onset of extrinsic muscle activity generally preceded the onset of intrinsic muscle activation. Our findings provide evidence, in an in vivo rodent preparation, of respiratory modulation of motoneurons supplying intrinsic tongue muscles. Distinctions noted between intrinsic and extrinsic activities could be due to differences in motoneuron properties or the central, respiration-related control of each motoneuron population.

Three-dimensional architecture of the intrinsic tongue muscles, particularly the longitudinal muscle, by the chemical-maceration method

Muscle bundles of the transverse and vertical muscles of the tongue become flat when they enter the longitudinal muscle layers of the tongue, where they form a tunnel-like structure that surrounds the longitudinal muscle of the tongue. However, the three-dimensional architecture of longitudinal muscle fibers of the tongue has not been clarified. In the present study, we evaluated the function of the intrinsic muscles of the tongue by studying the three-dimensional architecture of the longitudinal muscle. Muscle bundles of the longitudinal muscle of the anterior part of a rabbit's tongue were exposed by the chemical-maceration and modified chemical-maceration methods and examined by scanning electron microscopy. In the longitudinal muscle of the tongue, muscle bundles running in the anteroposterior direction were arranged at regular intervals. These muscle bundles bifurcated or ramified at a sharp angle at each level from the superficial layer to the deep layer and joined or fused with adjacent muscle bundles. In addition, these ramified muscle bundles ran obliquely into shallower or deeper layers of the muscle, as well as in the same plane. Consequently, the longitudinal muscle of the tongue as a whole had a three-dimensional mesh-like structure. The transverse and vertical muscles of the tongue entered this mesh-like structure of muscle bundles of the longitudinal muscle as flat muscle bundles. The transverse and vertical muscles showed no ramification in the center of the tongue, where there is no longitudinal muscle. These results suggest that the three intrinsic muscles of the tongue are interlaced with one another and are bound tightly in the longitudinal muscle. This structure may enable the dorsum of the tongue to harden for pressing food during mastication and shifting the food posteriorly for swallowing.