Arytenoid Muscle Research Articles

The incidence, clinical features and risk factors for postoperative retropharyngeal hematoma and related dyspnea following anterior cervical discectomy and fusion: a single-center study of 10615 patients

BACKGROUND CONTEXTPostoperative retropharyngeal hematoma (PRH) and related dyspnea are rare but life-threatening complications following anterior cervical discectomy and fusion (ACDF) that require urgent recognition and treatment. However, current knowledge of PRH after ACDF is limited. Meanwhile, whether the morphological features of upper airway are the risk factors of PRH remains unknown. PURPOSEThe study aimed to investigate the incidence, clinical features, and risk factors, especially the morphological features of upper airway, of PRH and related dyspnea following ACDF. STUDY DESIGNA nested case‒control study. PATIENT SAMPLEConsecutive patients who underwent ACDF at a single institute from January 2010 to December 2021 were retrospectively reviewed. OUTCOME MEASURESThe outcome measures included the incidence, clinical features, intervention, outcome and risk factors for PRH and related dyspnea. METHODSAll patients with PRH were classified into the hematoma group. For each PRH subject, 3 control subjects without PRH were randomly selected as the control group. The clinical features, interventions and outcomes of patients were described. Potential risk factors were evaluated, including demographics, comorbidities, surgical characteristics, coagulation function, blood loss, preoperative blood pressure, and the morphological features of upper airway [prevertebral soft tissue thickness (PVT) and location of transverse arytenoid muscle (TAM) and epiglottis]. Univariate tests and multivariable logistic regression analysis were used to determine the risk factors for PRH. Subgroup analysis was also conducted for PRH patients with and without dyspnea. RESULTSAmong the 10615 patients who underwent ACDF, 18 (0.17%) developed PRH. The median time from the index surgery to PRH formation was 8.5 hours (25 and 75 percentile: 4 hours to 24 hours). All the PRH patients initially presented with wound swelling. Twelve (0.11%) patients presented dyspnea due to PRH, 2 of whom received urgent intubation and 1 of whom received emergent tracheotomy. All patients underwent hematoma evacuation, and most of them presented with completely relieved symptoms after evacuation, except for 1 patient who died from ischemic hypoxic encephalopathy. A level between the epiglottis and the TAM (LET) greater than 2, ossification of posterior longitudinal ligament (OPLL) and higher diastolic blood pressure (DBP) before surgery were found to be risk factors for PRH formation. Subgroup analysis revealed that a smaller prevertebral soft tissue thickness at C5 was associated with the development of dyspnea. CONCLUSIONThis study is the largest study to date focusing on the PRH and related dyspnea after ACDF. Our study showed that the incidences of PRH and related dyspnea after ACDF were 0.17% and 0.11%, respectively. The predominant symptoms of PRH were wound swelling and acute dyspnea. Most PRH cases occurred in the acute postoperative period. We demonstrated the risk factors for PRH to be (1) OPLL, (2) LET≥2 and (3) higher DBP before surgery and advocate paying increased attention to upper airway morphological features for identifying the risk of PRH after ACDF. With urgent recognition and timely intervention, severe clinical outcomes could be avoided.

Amount and spatial arrangement of muscle fibers in the human laryngealMusculus ventricularis.

Textbooks and atlases of human macroscopic and microscopic anatomy of the larynx generally provide, if at all, only sparse information on the laryngeal Musculus ventricularis. However, several studies indicate that this muscle takes over the function of vestibular (ventricular) fold phonation after denervation of the Musculus vocalis. In the present study, 29 laryngeal specimens were coronally dissected at different levels, i.e. the anterior (L1), middle (L2), and posterior third of the vestibular fold (L3), and they underwent histological analysis. In all specimens the vestibular folds of both hemi-larynxes contained striated muscle bundles in variable amounts, representing a ventricularis muscle. These muscle bundles obviously originated from the lateral (external) and thyroepiglottic part of the thyroarytenoid muscle and the aryepiglottic part of the oblique arytenoid muscle, as has been described by other authors. The areas of vestibular folds and their amounts of ventricularis muscle bundles were measured using image analysis software (imageJ) by manual tracing. The mean area of the vestibular folds of both hemi-larynxes was 27.9 mm2 (SD [standard deviation] ± 9.17), and the area occupied by fibers of the ventricularis muscle was 1.5 mm2 (SD ± 1.78). Statistical analysis comparing the areas of both hemi-larynxes and levels resulted in no significant differences, except for the levels 2 and 3. In level 2, significantly more muscle fibers (2.0 mm2 ; SD ± 2.21) were detectable within the vestibular fold than in level 3 (0.9 mm2 ; SD ± 1.43). Level 1 also contained more muscle fibers (1.1 mm2 ; SD ± 1.06) than level 3, however, without significance. In conclusion, the laryngeal ventricularis muscle is present in the majority of reported cases. Since the muscle is of clinical relevance, it should be included in anatomical textbooks by default.

Gross Morphological and Histological Features of Larynx in Yankasa Sheep ‎‎(Ovis aries)‎

The present study, conducted on the larynx of five adult Yankasa sheep of local breed, aimed at exploring its basic anatomy and histological features. The larynx consists of four cartilages; the unpaired epiglottis rostroventral, unpaired thyroid ventrally, dorsal paired arytenoid, and caudal unpaired cricoid. These cartilages presented distinct morphological features and were connected to each other by ligaments. The intrinsic laryngeal muscles include; the dorsal cricoarytenoid and transverse arytenoid muscles. The lateral cricoarytenoid was concealed by the thyroid laminae. The ventrally located thyroarytenoid and cricothyroid muscles. The laryngeal cavity comprised of rostral vestibule, a narrow middle glottic cleft and a wide infraglottic cavity caudally. Histologically, the epiglottis was lined by stratified squamous keratinized epithelium, the thyroid cartilage was lined by pseudostratified columnar epithelium, whereas the arytenoid cartilage was lined by pseudostratified columnar ciliated epithelium with goblet cells. The loose irregular loose connective tissue of the propria submucosa comprised of connective tissue cells mainly fibroblast, and fine blood capillaries, whereas the deeper part presented glandular tissues, ducts, fat cells and cartilages. It is envisaged that the study has provided basic information on gross and histological feature of the larynx in the Yankasa sheep.

Early-Stage Glottic Squamous Cell Carcinoma in the Era of Image-Guided Radiotherapy.

Early-stage squamous cell cancer (SCC) of the glottis has a good prognosis. Therefore, patients have long survival outcomes and may potentially suffer from late toxicities of radiotherapy. Radiotherapy with a conventional parallel-opposed-pair or anterior-oblique beam arrangements for stage 1 and 2 glottic SCC have field borders that traditionally cover the entire larynx, exposing organs-at-risk (e.g. carotid arteries, contralateral vocal cord, contralateral arytenoid and inferior pharyngeal constrictor muscles) to high radiation doses. The potential long-term risk of cerebrovascular events has attracted much attention to the dose that carotid arteries receive. Swallow and respiratory motion of laryngeal structures has been an important factor that previously limited reduction of the radiation treatment volume. Motion has been evaluated using multiple imaging modalities and this information has been used to calculate PTV margins for generation of more limited target volumes. This review discusses the current literature surrounding dose-effect relationships for various organs-at-risk and the late toxicities that are associated with them. This article also reviews the currently available data and effects of laryngeal motions on dosimetry to the primary target. We also review the current limitations and benefits of a more targeted approach of radiotherapy for early-stage glottic SCCs and the evolution of CT-based IGRT and MR-guided radiotherapy techniques that may facilitate a shift away from a conventional 3D-conformal radiotherapy approach.

Geographic variation in the laryngeal morphology of a widely distributed South-American anuran: behavioural and evolutionary implications

AbstractSound-producing organs generate acoustic signals that have a fundamental role in communication systems. In species exhibiting different biogeographic patterns, variations of these structures can explain a large part of interpopulation differences of their signals. Pleurodema thaul is an anuran with an extensive geographic distribution in Chile and presents an evident divergence in its acoustic signals among three genetic/bioacoustic groups (i.e. northern, central and southern). By means of classic histology and 3D-reconstructions, we study the geographic variation in the larynx of P. thaul males from these three groups. In addition, volumes of six laryngeal structures are used as predictors of acoustic characteristics of advertisement calls recorded in previous studies for the same subjects used in the current study. After removing the effect of body size, the arytenoid cartilage, dilator muscle and vocal cords show significant differences between the three bioacoustic groups. Furthermore, arytenoid cartilage and dilator muscle volumes predict some temporal parameters and also the dominant frequency of advertisement calls. Our results show important geographic variation in laryngeal morphology, which is in correspondence with acoustic, behavioural and genetic variation in this species.

Modified arytenoid muscle electrode recording method for neuromonitoring during thyroidectomy.

Intraoperative neuromonitoring (IONM) is an important application for protecting recurrent laryngeal nerve (RLN) during thyroid surgery. The method for recording arytenoid muscle electromyography (EMG) signals is reported to be feasible and reliable. However, the parameters of EMG signals are not provided. This study aimed to analyze the clinical characteristics of EMG signal parameters by modifying the insertion direction of needle electrodes. A total of 92 patients who were scheduled to undergo thyroidectomy were recruited. Two paired needle electrodes were inserted in bilateral angle points between rectus cricothyroid muscle and inferior margin of thyroid cartilage (TC) intraoperatively, and then the information from the EMG signals was recorded according to four-step method (V1-R1-R2-V2). Pre-and post-operative laryngo-fiberoscopy was performed to confirm the vocal cord function. A total of 122 RLNs were successfully recorded during thyroidectomy, with the mean EMG amplitude and latency were 1,857±1,718/2,347±2,323 µV and 3.89±1.12/2.26±0.05 ms for V1/R1 signals before resection, and 1,924±1,705/2,450±2,345 µV and 3.87±1.17/2.27±0.08 ms for R2/V2 signals after resection. There were no significant changes before and after resection, and a normal vocal cord movement was observed postoperatively. The amplitude of left nerves was higher than that of the right ones. Furthermore, the latency of the right vagus was shorter than the left ones, but there was no difference in the amplitude and latency between age, sex and pathological types. Modified arytenoid muscle EMG recording method was considered to be safe, feasible and reliable. The latency of right vagus EMG signals were shorter than the left ones, and the amplitude of EMG signals might be related to different sides.

Ex vivo investigation of the effect of the transverse arytenoid ligament on abduction of the arytenoid cartilage when performing equine laryngoplasty

ABSTRACTAims: To investigate the effect of the transverse arytenoid ligament (TAL) on abduction of the arytenoid cartilage when performing laryngoplasty.Methods: Modified prosthetic laryngoplasty was performed on right and left sides of 13 cadaver larynges. Increasing force was sequentially applied to the left arytenoid cartilage at 3 N intervals from 0–24 N, when the force on the right arytenoid cartilage was either 0 or 24 N, before and after TAL transection. Digital photographs of the rostral aspect of the larynx were used to determine the left arytenoid abduction angles for these given force combinations and results compared before and after TAL transection. Longitudinal and transverse sections of the TAL from seven other equine larynges were also examined histologically.Results: Increasing force on the left arytenoid cartilage from 0–24 N produced a progressive increase in the angle of the left arytenoid cartilage (p < 0.001) and increasing force on the right arytenoid cartilage from 0–24 N reduced the angle of the left arytenoid cartilage (p < 0.001). Following transection of the TAL the mean angle of the left arytenoid increased from 36.7 (95% CI = 30.5–42.8)° to 38.4 (95% CI = 32.3–44.5)°. Histological examination showed that the TAL was not a discrete ligament between the arytenoid cartilages but was formed by the convergence of the ligament and the left and right arytenoideus transversus muscles.Conclusions: Transection of the TAL in ex vivo equine larynges enabled greater abduction of the left arytenoid cartilage for a given force. These results indicate that TAL transection in conjunction with prosthetic laryngoplasty may have value, but the efficacy and safety of TAL transection under load in vivo, and in horses clinically affected with recurrent laryngeal neuropathy must be evaluated.Abbreviations: Fmax: Force needed to maximally abduct the left or right arytenoid; TAL: Transverse arytenoid ligament

Switching of the Laryngeal Cavity From the Respiratory Diverticulum to the Vestibular Recess: A Study Using Serial Sagittal Sections of Human Embryos and Fetuses

A cecum-like protrusion of the pharynx (the laryngeal cecum or vestibular recess [VR]) develops immediately anterior to the laryngeal part of the respiratory diverticulum. An expansion of the VR has been well described, whereas the fate of the diverticulum is still obscure, although its pharyngeal opening corresponds to the glottis. We observed sagittal sections of 10 embryos (five specimens at 5-6weeks and another five at 7-8weeks) and eight fetuses at 25-30weeks. At 5-6weeks, a lumen of the laryngeal part of the respiratory diverticulum appeared, and subsequently, the VR opened into the epithelial lamina. Because of this discrete separation, it seemed unlikely that the pharyngeal pouches contributed to the laryngeal epithelium. At 6-7weeks, the VR exhibited a high boot-shaped lumen with canalization to the diverticular lumen at the level of the cricoid cartilage. Thus, in a midline area between the bilateral arytenoid cartilages, double laryngeal lumina were evident, separated by the thick midline epithelial lamina. At 25-30weeks, the inferior part of the VR lumen had become enlarged because of the destruction of the epithelial lamina along the arytenoid and corniculate cartilages. In contrast, candidates for the initial diverticular lumen remained as epithelial slits in the anterosuperior side of the transverse arytenoid muscle. Therefore, the final anterior and lateral laryngeal walls seemed to originate from the VR with canalization, in contrast to the part of the posterior wall derived from the initial diverticular wall.

Analysis of therapeutic methods for treating vocal process granulomas

Conclusion: The combination of laryngeal microsurgery and local injections of botulinum toxin type A (BTA) can increase the cure rate of patients with vocal process granulomas (VPGs). Objective: To analyze the therapeutic effects of conservative treatments, microsurgical resection with suturing and microsurgery in combination with local injections of BTA for the treatment of VPGs. Methods: A retrospective analysis of 168 cases of VPG was performed. All of the patients initially received a conservative treatment. Some of the patients who did not respond to the conservative treatments were treated using microsurgical resection and microsuturing using an 8-0 absorbable filament. Other patients additionally received a four-point injection of BTA into the thyroarytenoid muscle and the arytenoid muscle on the operated side. Results: The lesions of 41.3% (71/168) of the patients who were given the conservative treatments (including acid suppression, vocal rest, and voice therapy) disappeared, and the lesions of 10.7% (18/168) of the patients were reduced. The conservative treatments were unsuccessful for 47% (79/168) of the patients. The cure rate was 78.4% (29/37) for the patients who were treated by microscope resection using a CO2 laser and microsuturing of the surrounding mucosa. Of the eight patients who experienced a recurrence, five of them had lesions that disappeared after 3 months of conservative treatment, whereas the other three patients recovered after a second operation. The cure rate of the 42 patients who were treated using microsurgery combined with local injections of BTA was 95.2% (40/42), with only 2 cases of recurrence at 2 months post-treatment.

Terminal Branch of Recurrent Human Laryngeal Nerve

The importance of the recurrent laryngeal nerve in surgery on the anterior region of the neck has motivated many published papers on critical points of its pathway, relationship with the inferior thyroid artery, penetration in the larynx, division outside the larynx, and branches communicating with the internal branch of the superior laryngeal nerve. We analyze the terminal branches of the recurrent laryngeal nerve and their distribution through the laryngeal muscles. 44 laryngeal nerves had been dissected. Most frequently, the recurrent laryngeal nerve presents a division below or at the level of the lower margin of the cricoid cartilage (outside the larynx). One of these branches forms the communication with the internal branch of the superior laryngeal nerve, and the other penetrates the laryngeal space. Above the lower margin of the cricoid cartilage, the inferior laryngeal nerve issues a variable number of branches to muscles (3 to 7): to the posterior cricoarytenoid muscle; to the oblique and transversal arytenoid muscles; and to the lateral cricoarytenoid muscle and the thyroarytenoid muscle.

Laryngeal nerve “anastomoses”

Laryngeal nerves have been observed to communicate with each other and forma variety of patterns. These communications have been studied extensively and have been of particular interest as it may provide an additional form of innervation to the intrinsic laryngeal muscles. Variations noted in incidence may help explain the variable position of the vocal folds after vocal fold paralysis. This study aimed to examine the incidence of various neural communications and to determine their contribution to the innervation of the larynx. Fifty adult cadaveric en-bloc laryngeal specimens were studied. Three different types of communications were observed between internal and recurrent laryngeal nerves viz. (1) Galen's anastomosis (81%):in 13%, it was observed to supply the posterior cricoarytenoid muscle; (2) thyroarytenoid communication (9%): this was observed to supply the thyroarytenoid muscle in 2% of specimens and (3) arytenoid plexus (28%): in 6%, it supplied a branch to the transverse arytenoid muscle. The only communication between the external and recurrent laryngeal nerves was the communicating nerve (25%). In one left hemi-larynx, the internal laryngeal nerve formed a communication with the external laryngeal nerve, via a thyroid foramen. The neural communications that exist in the larynx have been thought to play a role in laryngeal innervation. The results of this study have shown varying incidences in neural communications. Contributions from these communications have also been noted to various intrinsic laryngeal muscles which may be a possible factor responsible for the variable position of the vocal folds in certain cases of vocal fold paralysis.

Functional role of human laryngeal nerve connections

Current knowledge of the functional role of human laryngeal nerves is based on traditional laryngeal neuroanatomic descriptions or contradictory electromyographic studies. The aim of this study was to clarify the functional role of neural connections between laryngeal nerves by correlating the different electromyographic patterns observed after laryngeal stimulation and the existence of different neural connections. Descriptive. Electromyographic and morphologic study in 13 patients during total laryngectomy procedure. Seven patients showed an additional evoked response from the cricothyroid muscle after recurrent laryngeal nerve stimulation. External laryngeal nerve stimulation resulted in additional responses from the posterior cricoarytenoid muscle in three cases and from the arytenoid muscle in one. The presence of a neural connection was confirmed in all patients who showed an unexpected electromyographic response. The different connections between laryngeal nerves are at least partially of motor nature and play a role in the mobility of vocal folds.

The clinical interest of the ary‐thyro‐cricoid fascicle

The aim of this work was to study the prevalence and form of the ary-thyro-cricoid (ATC) muscular fascicle, a variable muscular slip connecting the oblique and/or transverse arytenoid muscles with the thyroarytenoid (TA) and/or lateral cricoarytenoid (LCA) muscles resembling a sphincter encircling the glottis. Thirty larynges obtained from necropsies of individuals with no known laryngeal pathology were dissected. The ATC fascicle was observed in 96.7% of the larynges. It appeared bilaterally in 60% of subjects and unilaterally in 36.7%. The posterior attachment of the muscular slip was observed to be in common with either the transverse arytenoid (34%), or the oblique arytenoid (28%) or both muscles (38%). Its fibers terminated by intermingling with either those of the LCA muscle (10.6%), or the TA muscle (38.3%) or both (51.1%). These variable attachments mean that there are nine possible variants of this muscular fascicle. The ATC fascicle was supplied by branches originating bilaterally from the recurrent laryngeal (RLN) and internal laryngeal nerves. The existence of this ATC fascicle could explain the variable position (intermediate, paramedian or lateral) adopted by the vocal folds after lesion of the RLN. The bilateral disposition and innervation of the fascicle could also complicate the interpretation of electromyographic techniques used for testing laryngeal nerve function.

Use of a single bipolar electrode in the posterior arytenoid muscles for bilateral monitoring of the recurrent laryngeal nerves in thyroid surgery

The aims were to assess the technical feasibility of using a single electrode in the posterior arytenoid muscles (PAM) for intraoperative monitoring of the recurrent laryngeal nerve (RLN) in thyroid surgery, to validate the new method against the insertion of electrodes placed in the vocal cord muscle, and to report the results of the clinical application of the new concept. A total of 52 patients were enrolled. The handling and safety of RLN monitoring was tested by simultaneous registration of the EMG response from vocal fold electrodes and PAM electrodes. Acoustically and electromyographically we found nearly the same values for the arytenoid muscles as for the vocal folds, although the signals taken from the vocal folds were slightly stronger. PAM recording using a single bipolar electrode is technically feasible and as reliable compared to the standard vocal cord monitoring.

Ventroaxial Luxation of the Apex of the Corniculate Process of the Arytenoid Cartilage in Resting Horses During Induced Swallowing or Nasal Occlusion

To report ventroaxial luxation of the apex of the left or right corniculate process of the arytenoid cartilage under the contralateral corniculate process during resting endoscopic examination, and morphologic features of the larynx of 1 affected horse. Retrospective study. Horses (n=8). Horses had endoscopic examination as part of a survey of Clydesdale horses (n=7), or investigation of poor performance in Thoroughbred horses (1). One Clydesdale was euthanatized and the larynx examined; 4 cadaver larynges from normal horses were also examined. Ventroaxial luxation of the apex of the left or right corniculate process of the arytenoid cartilage was not detected during quiet breathing but was induced by swallowing or nasal occlusion. Prevalence in Clydesdales was 5.2% (7/133). A Thoroughbred with identical endoscopic appearance of the larynx at rest had progressive ventroaxial luxation of the apex of the arytenoid cartilage during high-speed treadmill endoscopy, associated with abnormal respiratory noise. Necropsy examination of an affected Clydesdale larynx revealed an excessively wide (10 mm) transverse arytenoid ligament that allowed easy separation of the apices of the corniculate processes. In normal cadaver larynges, the apices could not be separated with abaxial traction. The clinical relevance of this laryngeal observation in resting horses is unclear. Ventroaxial luxation of the corniculate process of the arytenoid cartilage during induced swallowing or nasal occlusion in resting horses or during high-speed treadmill exercise may be caused by an abnormally wide transverse arytenoid ligament.

Laryngeal Neurilemmoma: A Case Report

Published reports of benign nerve sheath tumors of the larynx are extremely rare. Because these tumors represent a potential threat to the airway, prompt diagnosis and treatment are vital. We report a case of a neurilemmoma that arose from the right arytenoid muscle adjacent to the arytenoid cartilage. The mass was completely excised, and no recurrence was observed during follow-up. We discuss the diagnosis and management of this rare tumor.

Atypical anastomosis of laryngeal nerves

The larynx and its associated structures derive their chief source of innervation from the superior and recurrent laryngeal nerves. Surgery of the larynx requires a sound knowledge of the normal anatomy as well as variations that may be encountered in this region. We report the presence of rare communications between the right external and internal laryngeal nerves as well as between the right external and inferior laryngeal nerves via a thyroid foramen. In addition, we report on bilateral innervation of the respective ipsilateral aryepiglottic, transverse, and oblique arytenoid muscles by the internal laryngeal nerve, which is contrary to the classical descriptions of this nerve. The anatomic features are described and clinical implications are highlighted.

Variability in Nerve Patterns of the Adductor Muscle Group Supplied by the Recurrent Laryngeal Nerve

Accurate knowledge of the nerve supply of each individual muscle is needed to achieve a successful selective reinnervation of the larynx. The aim of the present work was to study the nerve supply of the adductor laryngeal muscles supplied by the recurrent laryngeal nerve. Morphologic study of human larynges. The muscular nerve supply was studied in a total sample of 75 human larynges obtained from necropsies (47 males and 28 females, age range from 41-95 years) and examined by careful dissection using a surgical microscope. The arytenoid muscle received one branch from each recurrent nerve. In 88% of cases, this branch arose in a common trunk with the upper branch of the posterior cricoarytenoid muscle. In 8% of cases, the nerve for the arytenoid muscle also had a branch going to the lateral cricoarytenoid muscle. The arytenoid muscle also received from one to three pairs of branches from the posterior division of the internal laryngeal nerve; these were interconnected ipsi- and contralaterally and were also connected to the two branches coming from the recurrent laryngeal nerve. The lateral cricoarytenoid muscle received from one to six branches from the recurrent nerve, but in 5.8% of cases, it also received a twig from a connecting branch between the recurrent nerve and the external (5.6%) or the internal laryngeal nerves (0.2%). The thyroarytenoid muscle received from one to four branches from the recurrent nerve, but in 5.6% of cases, it also received a twig from a connecting branch between the recurrent nerve with the external (4.6%) or the internal (1%) laryngeal nerves. No abductor or adductor division of the recurrent laryngeal nerve was found in the present study. In 88% of cases, the nerve supply to the arytenoid muscle (adductor) and the posterior cricoarytenoid muscle (abductor) arose from a common trunk, which in 8% of cases, also had a branch to the lateral cricoarytenoid muscle. Furthermore, the high incidence of branches innervating the adductor muscles from connections between the recurrent laryngeal nerve and the internal and external laryngeal nerves led us to reconsider the contribution of these nerves in the supply to this muscle group.

Functional Anatomy of the Human Intrinsic Laryngeal Muscles

BACKGROUND: Since the beginning of the Christian era, numerous reports have dealt with the construction and functional organization of the larynx, thus stressing its role as the keystone of vocalization in vertebrates. The purpose of this review is to provide a comprehensive summary of basic anatomical facts and to point out certain new aspects of the innervation of laryngeal muscles. METHODS: The data presented herein were collected from a preliminary gross anatomical study performed in six human individuals at our institute, and from published literature. RESULTS: The basic framework of the human larynx is composed of the hyaline thyroid, cricoid and arytenoid cartilages, the fibroelastic epiglottis and the hyoid bone. Two pairs of synovial articulations, i.e. the cricothyroid and cricoarytenoid joints, provide the mobility needed to adjust the tension of the vocal ligaments. The intrinsic laryngeal muscles may be divided into three functional groups: (i) muscles varying the rima glottidis (the transverse arytenoid as well as the lateral and posterior cricoarytenoid muscles); (ii) muscles regulating tension in the vocal ligaments (i.e. the cricothyroid, posterior cricoarytenoid as well as the compound thyroarytenoid and vocalis muscles) and (iii) muscles modifying the laryngeal inlet (the so-called ‘sphincter aditus’, which is formed by the oblique arytenoid and aryepiglottic muscles and counteracted by the thyroepiglottic muscle). They are innervated by the superior and inferior laryngeal nerves branching off the vagus nerve. The external branch of the superior laryngeal nerve exclusively supplies the cricothyroid muscle. There is strong evidence that the lateral cricoarytenoid and the thyroarytenoid muscles are solely supplied by the inferior laryngeal nerve. All other intrinsic laryngeal muscles seem to receive motor fibres either from both laryngeal nerves or from the internal branch of the superior laryngeal nerve alone. CONCLUSIONS: Thus, the traditional concept of motor innervation of the larynx seems to be out of date. In fact, the internal branch of the superior laryngeal nerve should no longer be seen as purely sensory but rather – as also the inferior laryngeal nerve – as a mixed nerve containing sensory as well as motor fibres.

Non-invasive monitoring of functionally distinct muscle activations during swallowing

Objectives: Dysphagia is an important consequence of many diseases. As some of the muscles of deglutition tend to be deep to the surface, needle electrodes are typically used, but this limits the number of muscles that can be simultaneously recorded. Since control of swallowing involves central pattern generators (CPGs) which distribute commands to several muscles, monitoring several muscles simultaneously is desirable. Here we describe a novel method, based on computing the independent components (ICs) of the simultaneous sEMG recordings (Muscle Nerve Suppl 9 (2000) 9) to detect the underlying functional muscle activations during swallowing using only surface EMG (sEMG) electrodes. Methods: Seven normal subjects repeatedly swallowed liquids of varying consistency while sEMG was recorded from 15 electrodes from the face and throat. Active areas of EMG were excised from the recordings and the ICs of the sEMG were calculated. Results: The ICs demonstrated less swallow-to-swallow variability than the raw sEMG. The ICs, each consisting of a unique temporal waveform and a spatial distribution, provided a means to segregate the complex sequence of muscle activation into rigorously defined separate functional units. The temporal profiles of the ICs and their spatial distribution were consistent with prior needle EMG studies of the cricopharyngeal, superior pharyngeal constrictor, submental and possibly arytenoid muscles. Other components appeared to correspond to EKG artifact contaminating the EMG recordings, laryngeal excursion, tongue movement and activation of the buccal and/or masseter musculature At least two of the components were affected by the consistency of the liquids swallowed. Re-testing one subject a week later demonstrated good intertrial reliability. Conclusions: We propose that the ICs of the sEMG provide a non-invasive means to assess the complex muscle sequence activation of deglutition.