Intrinsic Laryngeal Muscles Research Articles

Asymmetric triangular body-cover model of the vocal folds with bilateral intrinsic muscle activation.

Many voice disorders are linked to imbalanced muscle activity and known to exhibit asymmetric vocal fold vibration. However, the relation between imbalanced muscle activation and asymmetric vocal fold vibration is not well understood. This study introduces an asymmetric triangular body-cover model of the vocal folds, controlled by the activation of bilateral intrinsic laryngeal muscles, to investigate the effects of muscle imbalance on vocal fold oscillation. Various scenarios were considered, encompassing imbalance in individual muscles and muscle pairs, as well as accounting for asymmetry in lumped element parameters. Measurements of amplitude and phase asymmetries were employed to match the oscillatory behavior of two pathological cases: unilateral paralysis and muscle tension dysphonia. The resulting simulations exhibit muscle imbalance consistent with expectations in the composition of these voice disorders, yielding asymmetries exceeding 30% for paralysis and below 5% for dysphonia. This underscores the relevance of muscle imbalance in representing phonatory scenarios and its potential for characterizing asymmetry in vocal fold vibration.

Transcriptome Analysis of Left Versus Right Intrinsic Laryngeal Muscles Associated with Innervation.

Recurrent laryngeal nerve injury diagnosed as idiopathic or due to short-term surgery-related intubation exhibits a higher incidence of left-sided paralysis. While this is often attributed to nerve length, it is hypothesized there are asymmetric differences in the expression of genes related to neuromuscular function that may impact reinnervation and contribute to this laterality phenomenon. To test this hypothesis, this study analyzes the transcriptome profiles of the intrinsic laryngeal muscles (ILMs), comparing gene expression in the left versus right, with particular attention to genetic pathways associated with neuromuscular function. Laboratory experiment. RNA was extracted from the left and right sides of the rat posterior cricoarytenoid (PCA), lateral thyroarytenoid (LTA), and medial thyroarytenoid (MTA), respectively. After high-throughput RNA-Sequencing, 88 samples were organized into 12 datasets according to their age (P15/adult), sex (male/female), and muscle type (PCA/LTA/MTA). A comprehensive bioinformatics analysis was conducted to compare the left-right ILMs across different conditions. A total of 774 differentially expressed genes were identified across the 12 experimental groups, revealing age, sex, and muscle-specific differences between the left versus right ILMs. Enrichment analysis of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways implicated several genes with a left-right laryngeal muscle asymmetry. These genes are associated with neuronal and muscular physiology, immune/inflammatory response, and hormone control. Bioinformatics analysis confirmed divergent transcriptome profiles between the left-right ILMs. This preliminary study identifies putative gene targets that will characterize ILM laterality. N/A Laryngoscope, 134:3741-3753, 2024.

Don't Throw the Baby Out with the Bathwater: The Muscular Basis for Register Adjustment

Abstract: Registration in singing has long been considered to have its basis in adjustments of the intrinsic laryngeal musculature, but most pedagogues also agree that there is an acoustic or resonance component to the production or perception of vocal registers. Shifts in thinking about register adjustment may have led some pedagogues to concentrate on resonance adjustments to produce a particular quality, sometimes without adequate attention to balanced muscle use. This article provides some context for pedagogic consideration of pitch/register adjustment and examples of what can happen if muscular balance is not optimized in singing training for all genres.

Presentation of Arteria Lusoria with Non Recurent Laryngeal Nerve.

Non-recurrent laryngeal nerve (NRLN) is an anatomic variation seen in about 0.52-0.7% patients, generally on right side. It exits the vagus nerve having a direct route to the larynx, unlike usual recurrent laryngeal nerve, supplying intrinsic laryngeal muscles except cricothyroid. It is sited over left side on extremely rare occasions, that is, 0.04% of the cases. Some cases of NRLN co-exists with aberrant right subclavian artery which courses behind the esophagus, also known as 'arteria lusoria'. Here we present a case of 60-years old patient, diagnosed as goiter presented to us in june 2023 at the department of head and neck surgery at a tertiary care setup of Karachi Pakistan. Intra-operatively, non-recurrent nerve was encountered, whose association was found with arteria lusoria, observed in pre-operative CT-scan. The nerve was saved and no post-operative complications were seen in patient. The association of arteria lusoria in this case emphasize its importance in predicting NRLN via pre-operative imaging techniques which can prevent its injury intra-operatively.

Netrin-1 as A neural guidance protein in development and reinnervation of the larynx

Neural guidance proteins participate in motor neuron migration, axonal projection, and muscle fiber innervation during development. One of the guidance proteins that participates in axonal pathfinding is Netrin-1. Despite the well-known role of Netrin-1 in embryogenesis of central nervous tissue, it is still unclear how the expression of this guidance protein contributes to primary innervation of the periphery, as well as reinnervation. This is especially true in the larynx where Netrin-1 is upregulated within the intrinsic laryngeal muscles after nerve injury and where blocking of Netrin-1 alters the pattern of reinnervation of the intrinsic laryngeal muscles. Despite this consistent finding, it is unknown how Netrin-1 expression contributes to guidance of the axons towards the larynx. Improved knowledge of Netrin-1’s role in nerve regeneration and reinnervation post-injury in comparison to its role in primary innervation during embryological development, may provide insights in the search for therapeutics to treat nerve injury. This paper reviews the known functions of Netrin-1 during the formation of the central nervous system and during cranial nerve primary innervation. It also describes the role of Netrin-1 in the formation of the larynx and during recurrent laryngeal reinnervation following nerve injury in the adult.

Register transitions in an in vivo canine model as a function of intrinsic laryngeal muscle stimulation, fundamental frequency, and sound pressure level.

Phonatory instabilities and involuntary register transitions can occur during singing. However, little is known regarding the mechanisms which govern such transitions. To investigate this phenomenon, we systematically varied laryngeal muscle activation and airflow in an in vivo canine larynx model during phonation. We calculated voice range profiles showing average nerve activations for all combinations of fundamental frequency (F0) and sound pressure level (SPL). Further, we determined closed-quotient (CQ) and minimum-posterior-area (MPA) based on high-speed video recordings. While different combinations of muscle activation favored different combinations of F0 and SPL, in the investigated larynx there was a consistent region of instability at about 400 Hz which essentially precluded phonation. An explanation for this region may be a larynx specific coupling between sound source and subglottal tract or an effect based purely on larynx morphology. Register transitions crossed this region, with different combinations of cricothyroid and thyroarytenoid muscle (TA) activation stabilizing higher or lower neighboring frequencies. Observed patterns in CQ and MPA dependent on TA activation reproduced patterns found in singers in previous work. Lack of control of TA stimulation may result in phonation instabilities, and enhanced control of TA stimulation may help to avoid involuntary register transitions, especially in the singing voice.

Development of the hyolaryngeal architecture in horseshoe bats: insights into the evolution of the pulse generation for laryngeal echolocation

BackgroundThe hyolaryngeal apparatus generates biosonar pulses in the laryngeally echolocating bats. The cartilage and muscles comprising the hyolarynx of laryngeally echolocating bats are morphologically modified compared to those of non-bat mammals, as represented by the hypertrophied intrinsic laryngeal muscle. Despite its crucial contribution to laryngeal echolocation, how the development of the hyolarynx in bats differs from that of other mammals is poorly documented. The genus Rhinolophus is one of the most sophisticated laryngeal echolocators, with the highest pulse frequency in bats. The present study provides the first detailed description of the three-dimensional anatomy and development of the skeleton, cartilage, muscle, and innervation patterns of the hyolaryngeal apparatus in two species of rhinolophid bats using micro-computed tomography images and serial tissue sections and compares them with those of laboratory mice. Furthermore, we measured the peak frequency of the echolocation pulse in active juvenile and adult individuals to correspond to echolocation pulses with hyolaryngeal morphology at each postnatal stage.ResultsWe found that the sagittal crests of the cricoid cartilage separated the dorsal cricoarytenoid muscle in horseshoe bats, indicating that this unique morphology may be required to reinforce the repeated closure movement of the glottis during biosonar pulse emission. We also found that the cricothyroid muscle is ventrally hypertrophied throughout ontogeny, and that the cranial laryngeal nerve has a novel branch supplying the hypertrophied region of this muscle. Our bioacoustic analyses revealed that the peak frequency shows negative allometry against skull growth, and that the volumetric growth of all laryngeal cartilages is correlated with the pulse peak frequency.ConclusionsThe unique patterns of muscle and innervation revealed in this study appear to have been obtained concomitantly with the acquisition of tracheal chambers in rhinolophids and hipposiderids, improving sound intensity during laryngeal echolocation. In addition, significant protrusion of the sagittal crest of the cricoid cartilage and the separated dorsal cricoarytenoid muscle may contribute to the sophisticated biosonar in this laryngeally echolocating lineage. Furthermore, our bioacoustic data suggested that the mineralization of these cartilages underpins the ontogeny of echolocation pulse generation. The results of the present study provide crucial insights into how the anatomy and development of the hyolaryngeal apparatus shape the acoustic diversity in bats.

Deep Learning for Neuromuscular Control of Vocal Source for Voice Production.

A computational neuromuscular control system that generates lung pressure and three intrinsic laryngeal muscle activations (cricothyroid, thyroarytenoid, and lateral cricoarytenoid) to control the vocal source was developed. In the current study, LeTalker, a biophysical computational model of the vocal system was used as the physical plant. In the LeTalker, a three-mass vocal fold model was used to simulate self-sustained vocal fold oscillation. A constant/ǝ/vowel was used for the vocal tract shape. The trachea was modeled after MRI measurements. The neuromuscular control system generates control parameters to achieve four acoustic targets (fundamental frequency, sound pressure level, normalized spectral centroid, and signal-to-noise ratio) and four somatosensory targets (vocal fold length, and longitudinal fiber stress in the three vocal fold layers). The deep-learning-based control system comprises one acoustic feedforward controller and two feedback (acoustic and somatosensory) controllers. Fifty thousand steady speech signals were generated using the LeTalker for training the control system. The results demonstrated that the control system was able to generate the lung pressure and the three muscle activations such that the four acoustic and four somatosensory targets were reached with high accuracy. After training, the motor command corrections from the feedback controllers were minimal compared to the feedforward controller except for thyroarytenoid muscle activation.

Next-Generation Sequencing Application: A Systematic Approach for High-Quality RNA Isolation from Skeletal Muscles.

RNA extraction and analyses from tissues using bulk RNA-Sequencing (RNA-Seq) provide a more accurate picture of the gene expression compared to other molecular biology techniques for RNA quantification. Challenges associated with high-quality RNA extraction from skeletal muscles require a modification of standard protocols. Here, we describe a procedure for high-quality RNA isolation from intrinsic laryngeal muscles transferable to skeletal muscles with comparable technical and biological difficulties. Standard protocols for RNA isolation were optimized by maximizing the pooling strategy, determining the sample weight, applying cryogenic muscle disruption, and incorporating RNase-inhibiting reagents during the tissue preparation steps.

Neurectomy and Myomectomy for Treatment of Spasmodic Dysphonia.

Spasmodic dysphonia (SD) is a debilitating neurological disorder affecting the muscles of voice production. Sudden involuntary movements of the vocal folds lead to phonatory breaks and to forced, strained, and strangled voice quality in adductor SD, or breathy breaks in abductor SD. There is currently no cure for spasmodic dysphonia, and the gold standard for treatment is the injection of botulinum toxin in small amounts to the intrinsic laryngeal musculature.1 However, botulinum treatment requires periodic reinjection, produces vocal instability immediately after injection, lacks uniform results among patients, and patients can develop antibodies to botulinum toxin. Long-term or permanent symptom relief would be ideal. We present four patients with adductor and one patient with abductor spasmodic dysphonia who underwent neurectomy and myomectomy for treatment. The mean age was 64 years (age range 45-83). The mean duration of adductor spasmodic dysphonia was 11.8 years. The duration of abductor spasmodic was 4 years. All patients had previously been treated with voice therapy and botulinum toxin A. The mean duration of follow up was 1.7 years. Four patients had subjective and objective improvement after surgery. One patient had subjective improvement.

Reliability of Phonemically Loaded Sentences in Spanish for Identifying Laryngeal Dystonia by Non-Spanish Speaking Speech-Language Pathologists

Laryngeal dystonia (LD) is a focal dystonia affecting the intrinsic laryngeal muscles. Clinical diagnosis requires subjective evaluation by experienced clinicians and is primarily based on auditory-perceptual assessment. Several speech tasks are widely accepted to elicit diagnosis specific auditory-perceptual symptoms of glottal stops in adductor LD or breathy breaks in abductor LD in spoken English. With the growing Spanish speaking population in the US and lack of Spanish speech tasks to assist in identifying LD in Spanish speaking subjects, assessing the reliability of phonemically loaded sentences in Spanish for use by non-Spanish speaking providers is critical. The first aim of this study was to develop and assess the reliability of a set of Spanish language phonemically loaded sentences designed to elicit signs and symptoms of LD. The second aim was to determine the effectiveness of non-Spanish speaking speech-language pathologists (SLPs) in identifying LD in Spanish speaking subjects using these stimuli. Phonemically loaded sentences were developed for this study following current guidelines for assessment of LD. Voice samples were obtained from native Spanish speaking individuals. Participant-speakers included 20 people with LD and 20 people without LD who served as controls. All participant-speakers were assessed by a Spanish-speaking laryngologist. Audio samples were presented to non-Spanish speaking SLPs with expertise in working with people with LD who served as raters and classified the samples as either presence or absence of LD. Kappa and the intra-class correlation coefficient were calculated and mixed effects logistic regression was used for prediction. The inter and intra-rater reliability indicated statistically significant agreement. Sensitivity, specificity, and predictive values for the diagnosis of LD by the raters were overall strong. Findings demonstrate that non-Spanish speaking SLPs with expertise in the assessment and treatment of LD can reliably identify the presence of LD using Spanish language stimuli in Spanish-speaking individuals. This study supports the use of newly developed Spanish language phonemically loaded voiced and voiceless sentences by English speaking clinicians as an effective tool for identifying LD in Spanish speakers, perhaps mitigating diagnostic delays experienced by patients with LD.

The larynx in 3 dimensions: A digital anatomical model derived from radiographic imaging, refined with peer-reviewed literature, and optimized with medical illustration

ObjectivesDevelopment of an anatomically accurate three-dimensional (3D) digital model of the human larynx derived from published literature and radiographic imaging. Materials and MethodsThe laryngeal framework was segmented from a computed tomography (CT) angiogram of a healthy 29-year-old female. Data derived from published anatomical studies were compiled to provide additional anatomical detail to each structure. Anatomical details beyond the resolution of the imaging study or which could not be elucidated from the study were refined according to descriptions in the anatomic literature. The 3D model was refined by the medical illustrator, and its mesh was reformatted to optimize online viewing and manipulation. ResultsDue to the small size of the laryngeal muscles, there was no attempt to segment these muscles using radiographic imaging. All intrinsic laryngeal muscles were generated de novo, as were the superior laryngeal nerve and recurrent laryngeal nerve. CT imaging was utilized to generate meshes of the hyoid bone, epiglottis, thyroid cartilage, cricoid cartilage, and thyrohyoid membrane. Additionally, the airway space was segmented to provide size and spatial location to the vallecula, false vocal folds, true vocal folds, piriform sinus, subglottis, and a scaffold for the mucosa. These meshes were processed to limit radiographic artifact and serve as a foundation for the construction of the remainder of the laryngeal anatomy. The model was uploaded to a 3D repository, which can be accessed here (https://shorturl.at/nJPYZ). ConclusionThe larynx is a highly specialized organ essential for speech, swallowing, and airway protection. This study describes a digital 3D model of the larynx, created by combining radiographic imaging with critical review of anatomic literature. Utilizing the expertise of neuroradiology, laryngeal surgery, and medical illustration, we highlight surgically-relevant anatomic relationships and important aspects to consider during laryngeal surgery.

Domestic cat larynges can produce purring frequencies without neural input

Most mammals produce vocal sounds according to the myoelastic-aerodynamic (MEAD) principle, through self-sustaining oscillation of laryngeal tissues.1,2 In contrast, cats have long been believed to produce their low-frequency purr vocalizations through a radically different mechanism involving active muscle contractions (AMC), where neurally driven electromyographic burst patterns (typically at 20-30Hz) cause the intrinsic laryngeal muscles to actively modulate the respiratory airflow. Direct empirical evidence for this AMC mechanism is sparse.3 Here, the fundamental frequency (fo) ranges of eight domestic cats (Felis silvestris catus) were investigated in an excised larynx setup, to test the prediction of the AMC hypothesis that vibration should be impossible without neuromuscular activity, and thus unattainable in excised larynx setups, which are based on MEAD principles. Surprisingly, all eight excised larynges produced self-sustained oscillations at typical cat purring rates. Histological analysis of cat larynges revealed the presence of connective tissue masses, up to 4mm in diameter, embedded in the vocal fold.4 This vocal fold specialization appears to allow the unusually low fo values observed in purring. While our data do not fully reject the AMC hypothesis for purring, they show that cat larynges can easily produce sounds in the purr regime with fundamental frequencies of 25 to 30Hz without neural input or muscular contraction. This strongly suggests that the physical and physiological basis of cat purring involves the same MEAD-based mechanisms as other cat vocalizations (e.g., meows) and most other vertebrate vocalizations but is potentially augmented by AMC.

An Euler–Bernoulli-type beam model of the vocal folds for describing curved and incomplete glottal closure patterns

Incomplete glottal closure is a laryngeal configuration wherein the glottis is not fully obstructed prior to phonation. It has been linked to inefficient voice production and voice disorders. Various incomplete glottal closure patterns can arise and the mechanisms driving them are not well understood. In this work, we introduce an Euler–Bernoulli composite beam vocal fold (VF) model that produces qualitatively similar incomplete glottal closure patterns as those observed in experimental and high-fidelity numerical studies, thus offering insights into the potential underlying physical mechanisms. Refined physiological insights are pursued by incorporating the beam model into a VF posturing model that embeds the five intrinsic laryngeal muscles. Analysis of the combined model shows that co-activating the lateral cricoarytenoid (LCA) and interarytenoid (IA) muscles without activating the thyroarytenoid (TA) muscle results in a bowed (convex) VF geometry with closure at the posterior margin only; this is primarily attributed to the reactive moments at the anterior VF margin. This bowed pattern can also arise during VF compression (due to extrinsic laryngeal muscle activation for example), wherein the internal moment induced passively by the TA muscle tissue is the predominant mechanism. On the other hand, activating the TA muscle without incorporating other adductory muscles results in anterior and mid-membranous glottal closure, a concave VF geometry, and a posterior glottal opening driven by internal moments induced by TA muscle activation. In the case of initial full glottal closure, the posterior cricoarytenoid (PCA) muscle activation cancels the adductory effects of the LCA and IA muscles, resulting in a concave VF geometry and posterior glottal opening. Furthermore, certain maneuvers involving co-activation of all adductory muscles result in an hourglass glottal shape due to a reactive moment at the anterior VF margin and moderate internal moment induced by TA muscle activation. These findings have implications regarding potential laryngeal maneuvers in patients with voice disorders involving imbalances or excessive tension in the laryngeal muscles such as muscle tension dysphonia.

Improved vocal quality and decreased vocal effort after botulinum toxin treatment for laryngeal dystonia

Objectives: Laryngeal dystonia (LD) is characterized by irregular and involuntary task-specific spasms of the intrinsic laryngeal muscles. There is no curative treatment for it, however, laryngeal botulinum neurotoxin injections (BoNT-I) are considered the standard of care therapy. This study aims to characterize the population of LD patients and to assess the results of laryngeal BoNT-I.Methods: A Retrospective cohort study was conducted. Medical records were reviewed for all the patients with LD diagnosis seen in the Voice Unit of the Red de Salud UCChristus between January 2013 and October 2021. Biodemographic, clinical and treatment data were collected. Additionally, a telephonic survey was completed by the patients that underwent laryngeal BoNT-I, including self-reported voice outcomes and Voice Handicap Index 10 (VHI-10).Results: Of the 34 patients with LD included in the study, 23 received a total of 93 laryngeal BoNT-I and 19 completed the telephone survey. The majority (97%) of the injections corresponded to patients with adductor LD and 3% to abductor LD. Patients received a median of 3 (1–17) injections, with a more frequent cricothyroid approach (94.4%), while the thyrohyoid approach accounted for 5.6% of cases. Most injections were bilateral (96.8%). A significant improvement in the vocal quality and effort was noted after the last injection and the overall BoNT-I treatment (P < 0.001). Similarly, the VHI-10 score improved from a median of 31 (7–40) to 2 (0–19) (P < 0.001) after the last injection. A post-treatment breathy voice was reported in 95% of patients, and dysphagia to liquids and solids in 68% and 21%, respectively.Conclusions: Laryngeal BoNT-I is an effective treatment for LD, achieving an improvement in self-reported vocal quality and VHI-10 scores, and a reduction of the self-reported vocal effort. Adverse effects are mild in the majority of cases, constituting a safe and effective therapy for these patients.

Temporal Expression of Hox Genes and Phox2b in the Rat Nucleus Ambiguus During Development: Implications on Laryngeal Innervation.

Recurrent laryngeal nerve (RLN) injury results in synkinetic reinnervation and vocal fold paralysis. Investigation of cues expressed in the developing brainstem that influence correct selective targeting of intrinsic laryngeal muscles may elucidate post-injury abnormalities contributing to non-functional reinnervation. Primary targets of interest were Hoxb1 and Hoxb2, members of the Hox family that create overlapping gradients in the developing brain, and their target Phox2b, a transcription factor necessary for cranial nerve branchio- and visceromotoneuron survival. Rat embryos at developmental days E14, E16, E18, and E20 (4 animals/age) were sectioned for RNA in situ hybridization to detect Hoxb1, Hoxb2, and Phox2b mRNA within the brainstem. Slides were costained with Islet1 antibody for identification of the nucleus ambiguus. Results were confirmed using immunohistochemistry. Sections were imaged on a confocal microscope. RNA and protein expressions were quantified using QuPath. Statistical analyses were performed using R. Hoxb1, Hoxb2, and Phox2b expressions varied according to embryologic age. Hoxb1 and Hoxb2 expression peaked at E16, with significant decreases at E18 and E20 (one-way ANOVA p = 0.001 for both). Phox2b expression was highest at E14 and trended downward with increased embryologic age (one-way ANOVA p = 0.005). Peak expression of Hoxb1 and Hoxb2 is observed at time points when the RLN arrives at the larynx and begins to branch toward individual muscles, positioning these gene products to be involved in cueing laryngeal motoneuron identity and target identification. Higher expression of Phox2b earlier in development suggests a role in laryngeal motoneuron formation. NA Laryngoscope, 133:3462-3471, 2023.

Comparison of Botulinum Toxin Injections and Type 2 Thyroplasty for Adductor Spasmodic Dysphonia.

Injection of botulinum toxin type A (BTX) into intrinsic laryngeal muscles is the current gold standard therapy for adductor spasmodic dysphonia (AdSD). However, a surgical procedure could potentially offer more stable and long-lasting voice quality to AdSD patients. Here, we report the long-term results of type 2 thyroplasty (TP2) with TITANBRIDGE® (Nobelpharma, Tokyo, Japan) compared with those of BTX injections. In total, 73 AdSD patients visited our hospital between August 2018 and February 2022. Patients were provided the option of BTX injections or TP2. They were assessed via the Voice Handicap Index (VHI)-10 before treatments and at scheduled clinical follow-ups at 2, 4, 8, and 12 weeks for BTX and at 4, 12, 26, and 52 weeks for TP2. Overall, 52 patients selected the BTX injection and had a pre-injection mean VHI-10 score of 27.3 ± 8.8. Following injections, the scores significantly improved to 21.0 ± 11.1, 18.6 ± 11.5, and 19.4 ± 11.7 at 2, 4, and 8 weeks, respectively. There were no significant differences between the pre-injection scores and the 12-week scores (21.5 ± 10.7). Alternately, 32 patients opted to be treated with TP2 and had a pre-treatment mean VHI-10 score of 27.7. All patients reported an improvement in their symptoms. Additionally, the mean VHI-10 score significantly improved to 9.9 ± 7.4 at 52 weeks following treatment. There was a significant difference between the two treatment groups at 12 weeks. Some patients received both treatments. These preliminary results provide important insights into the value of TP2 as a potential permanent treatment for AdSD patients. 3 Laryngoscope, 133:3443-3448, 2023.

A review of the peripheral proprioceptive apparatus in the larynx.

The larynx is an organ of the upper airway that participates in breathing, glutition, voice production, and airway protection. These complex functions depend on vocal fold (VF) movement, facilitated in turn by the action of the intrinsic laryngeal muscles (ILM). The necessary precise and near-instantaneous modulation of each ILM contraction relies on proprioceptive innervation of the larynx. Dysfunctional laryngeal proprioception likely contributes to disorders such as laryngeal dystonia, dysphagia, vocal fold paresis, and paralysis. While the proprioceptive system in skeletal muscle derived from somites is well described, the proprioceptive circuitry that governs head and neck structures such as VF has not been so well characterized. For over two centuries, researchers have investigated the question of whether canonical proprioceptive organs, muscle spindles, and Golgi tendon organs, exist in the ILM, with variable findings. The present work is a state-of-the-art review of the peripheral component of laryngeal proprioception, including current knowledge of canonical and possible alternative proprioceptive circuitry elements in the larynx.

An optimized method for high-quality RNA extraction from distinctive intrinsic laryngeal muscles in the rat model

Challenges related to high-quality RNA extraction from post-mortem tissue have limited RNA-sequencing (RNA-seq) application in certain skeletal muscle groups, including the intrinsic laryngeal muscles (ILMs). The present study identified critical factors contributing to substandard RNA extraction from the ILMs and established a suitable method that permitted high-throughput analysis. Here, standard techniques for tissue processing were adapted, and an effective means to control confounding effects during specimen preparation was determined. The experimental procedure consistently provided sufficient intact total RNA (N = 68) and RIN ranging between 7.0 and 8.6, which was unprecedented using standard RNA purification protocols. This study confirmed the reproducibility of the workflow through repeated trials at different postnatal time points and across the distinctive ILMs. High-throughput diagnostics from 90 RNA samples indicated no sequencing alignment scores below 70%, validating the extraction strategy. Significant differences between the standard and experimental conditions suggest circumvented challenges and broad applicability to other skeletal muscles. This investigation remains ongoing given the prospect of therapeutic insights to voice, swallowing, and airway disorders. The present methodology supports pioneering global transcriptome investigations in the larynx previously unfounded in literature.

The inside-out surgical anatomy of the paraglottic space a video-guided endoscopic dissection.

The paraglottic space is an essential anatomic compartment of the larynx. It is central to the spread of laryngeal cancer and to the choice of conservative laryngeal surgery and many phonosurgical procedures. Since its description, 60 years ago, the surgical anatomy of the paraglottic space was sparsely revisited. Amid the era of endoscopic and transoral microscopic functional surgery of the larynx, we provide here a long-awaited description of the inside-out anatomy of the paraglottic space. Using an endoscope equipped with a 3D camera, we dissected 10 hemilarynges from 5 fresh frozen cadavers from the inside out. Before dissection, we labeled the vessels through injecting them with colored latex. We explored the paraglottic space emphasizing its shape, boundaries, and contents. We documented our findings through endoscopic photography and video recordings. The paraglottic space is a spacious tetrahedral space located parallel not only to the glottic, but also to the subglottic and the supraglottic compartments of the laryngeal lumen. It has musculo-cartilaginous, musculo-fibrous, and mucosal boundaries. It is separated from the pyriform sinus only by mucosa. A cushion of fat surrounds its vascular and to a lesser extent its neural contents. Harbored intrinsic laryngeal muscles are endoscopically identifiable within the space, namely the thyroarytenoid, the lateral, and posterior cricoarytenoid muscles. The endoscopic description of the paraglottic space partly fills the knowledge gap on the laryngeal anatomy from the inside out. It opens the door for novel diagnostic methods and for ultraconservative functional laryngeal interventions under endoscopic control. N/A.