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Comparative anatomy of the larynx and related structures
Abstract
Vocal impairment is a problem specific to humans that is not seen in other mammals. However, the internal structure of the human larynx does not have any morphological characteristics peculiar to humans, even compared to mammals or primates. The unique morphological features of the human larynx lie not in the internal structure of the larynx, but in the fact that the larynx, hyoid bone, and lower jawbone move apart together and are interlocked via the muscles, while pulled into a vertical position from the cranium. This positional relationship was formed because humans stand upright on two legs, breathe through the diaphragm (particularly indrawn breath) stably and with efficiency, and masticate efficiently using the lower jaw, formed by membranous ossification (a characteristic of mammals).This enables the lower jaw to exert a pull on the larynx through the hyoid bone and move freely up and down as well as regulate exhalations. The ultimate example of this is the singing voice. This can be readily understood from the human growth period as well. At the same time, unstable standing posture, breathing problems, and problems with mandibular movement can lead to vocal impairment.
... The larynx is an important organ associated with the protection of the airways (Saigusa, 2011), as well as the production of sound (Hare, 1986). It extends from the pharynx to the trachea and is generally composed of muscles, ligaments and cricoid, thyroid, epiglottis, and arytenoid cartilages (Hare, 1986;Junqueira & Carneiro, 2008). ...
... The larynx of animals and human beings have cartilaginous structures responsible for the functionality of this organ and therefore favor airway protection, breathing control, sound production, and speech propagation (Saigusa, 2011;Silva et al., 2014). The good performance of these mechanisms as well as the anatomical integrity of laryngeal cartilages is necessary for its normal functioning. ...
Armadillos, Xenarthras representatives, known for adaptability to different ecosystems, own specific morphophysiological characteristics that are not known and deserve to be studied. The aim of this study was to describe the morphology of cartilage of the larynx of the nine-banded armadillo (Dasypus novemcinctus). Five dead armadillos were donated by the Chico Mendes Institute of Biodiversity (ICMBio-PI) to the Federal University of Piauí. The animals were fixed and dissected for removal of the larynx. The cartilages were identified and described, photodocumented, and schematized. Fragments with about 0.5 cm of each cartilage were collected and submitted to classical histology for Hematoxylin-Eosin coloring. The slides were assembled in enterlan and analyzed under a light microscope. The larynx of the armadillo (D. novemcinctus) is located in the mentonian region, ventral to the esophagus, and due to the total positioning of the tongue in the oral cavity, there is also a cranial cervical position in this species. The larynx has five cartilages, they are: a cricoid, a thyroid, an epiglottis, and two arytenoids. The corniculate process is present; however, the cuneiform process is absent. The epiglottis has a discrete bifurcation at its apex. In all cartilages epithelial variations are observed. The tissues are varied from squamoso stratified to cylindrical pseudostratified, with propria lamina rich in mucoserosas glands. With the exception of epiglottic cartilage, predominantly elastic, the rest are hyaline. The larynx of D. novemcinctus, although the same number of cartilages, differs morphologically and microscopically from the larynx of other species.
... According to Souza Júnior et al. (2016), the larynx of bush dogs appears on the longitudinal axis in horizontal continuity with the mandibular body, corroborating the anatomical findings found in the paca. In this sense, Saigusa (2011) stated that this is a characteristic of quadrupedal mammals. As in humans, the larynx, in animals, has a respiratory and phonatory function, preventing food from entering the airways during swallowing (Brasil et al., 2005). ...
Paca (Cuniculus paca) has encouraged research as an experimental model both in the human medicine and veterinary, as well as the economic exploitation of its meat cuts, which favored its zootechnical use. There are no anatomical, microscopic descriptions and measurements of the larynx in this rodent. Eight pacas were dissected from the wild animal’s sector of the Faculty of Agricultural and Veterinary Sciences of the University of the State of São Paulo. The larynx was observed located in the ventral region of the neck, ventral to the esophagus, connecting the pharynx to the trachea, with cylindrical and irregular shape. Laryngeal cartilages (epiglottic, thyroid, cricoid and arytenoid) are interconnected and have different shapes. Thyroid showed greater length and width, compared to the others. Laryngeal cartilages were submitted to histological processing and stained with hematoxylin-eosin and Masson's trichrome. The epiglottic cartilage was stained with toluidine blue. Laryngeal cartilages thyroid, cricoid and the lower portion of the arytenoids are of hyaline origin and, in contrast, the epiglottis and the upper portion of the arytenoids are elastic. This latter cartilage demonstrated taste buds. The results will be able to auxiliate in veterinary care and as well as the conservation programs for this rodent.
... The laryngeal adductor reflex (LAR) is an involuntary airway protective response triggered by stimulation of sensory laryngeal receptors that appears highly conserved among species. 1 Afferent nerve activity travels via the internal branch of the superior laryngeal nerve (iSLN) to the brainstem. The efferent pathway is via the vagus and recurrent laryngeal nerves to the laryngeal adductor muscles, resulting in vocal fold closure and tracheobronchial airway protection. ...
Objective
The laryngeal adductor reflex (LAR) is an airway protective response triggered by sensory laryngeal receptors. It is unknown whether different glottic and supraglottic subsites vary in their reflex elicitation abilities. The recent discovery that a bilateral LAR is present in humans under general anesthesia upon laryngeal mucosal stimulation has enabled us to map the sensory receptor density for LAR elicitation at different laryngeal subsites. Our findings expose the likely mechanisms of LAR control.
Methods
Prospective series of 10 patients undergoing laryngoscopy. Laryngeal subsites (epiglottic tip, membranous vocal fold, midventricular vocal fold, posterior supraglottis, epiglottic petiole) were stimulated via direct laryngoscopy with a bipolar probe. Vocal fold responses were recorded by endotracheal tube and hook wire electrodes, and visual observation.
Results
Posterior supraglottic stimulation elicited bilateral LARs in all patients at all intensities. Membranous vocal folds, epiglottic petiole, and subglottis elicited no LAR. Ventricular fold and epiglottic tip responses converted from ipsi‐ to bilateral at high intensities.
Conclusion
There are likely three checkpoints for control of the LAR in humans. These checkpoints protect against inappropriate LAR activation during volitional tasks without compromising airway protection: 1) topographical differences in receptor density with the highest density in subsites most likely to contact foreign substances; 2) absence of receptors in membranous vocal folds; and 3) central summation threshold for crossed interneuron activation at brainstem level where only strong intensity stimuli will elicit bilateral responses. Checkpoint dysfunction provides a novel framework to diagnose and treat disease processes, including aspiration, laryngospasm, and sudden infant death.
Level of Evidence
4. Laryngoscope, 2018
... Morphologically, human larynx is definitely not different from the larynx of other mammals (Saigusa 2011). Animal models are predominantly used for larynx related-lessons in medical faculties and some morphological researches. ...
z Özkadif S, Dayan MO, Demiraslan Y, Aykut M, Özgel Ö. Yeni Zelanda tavşanında larynx ve tracheanın morfometrik özellikleri. Amaç: Bu çalışma Yeni Zelanda tavşanlarında larynx kıkır-dakları ile trachea'nın morfometrik özelliklerini araştırarak, cinsiyetler arasındaki farklılıkları ortaya koymak amacıyla gerçekleştirildi. Gereç ve Yöntem: Çalışmada 6 erkek, 6 dişi olmak üzere top-lam 12 adet sağlıklı erişkin Yeni Zelanda tavşanı kullanıldı. Baş ve boyun bölgesinin diseksiyonu sonucunda çıkartılan larynx kıkırdakları ve trachea'dan bazı ölçümler alınarak, istatistiki analiz yapıldı. İstatistiki önem P<0.05 düzeyinde belirlendi. Bulgular: Yapılan çalışma sonucunda Yeni Zelanda tavşanla-rında trachea ve larynx'in cinsiyetler arasında istatistiki ola-rak farklı olmadığı, sadece cartilago thyroidea'nın bazı ölçüm değerlerinde erkek ve dişiler arasında anlamlı fark olduğu tespit edildi. Öneri: Elde edilen bu morfometrik bilgilerin veteriner ana-tomi bilgi birikimine katkı sağlamasının yanısıra, oluşturula-bilecek olan model ve klinikte teşhis ve tedavi noktasında da bir ışık tutabileceği öngörülmektedir. Abstract Ozkadif S, Dayan MO, Demiraslan Y, Aykut M, Ozgel O. Morphometric properties of larynx and trachea in the New Zealand rabbit. Aim: This study was conducted to investigate the morpho-metric features of the larynx cartilages and trachea in New Zealand rabbits and reveal the differences between sexes. Material and Methods: In the study, the larynx cartilages belonging to a total of 12 healthy and adult New Zealand rabbits of both sexes (6 males, 6 females) were used. Some measurements were taken on the larynx cartilages and trachea, which had been taken out as a result of dissection of the head and neck, and statistical analyses were made. The statistical significance level was established at P<0.05. Results: Although the trachea and laynx related-measurements have no statistical difference between sexes, there was a statistical significance between sexes only in some values concerning the thyroid cartilage. Conclusion: In conclusion, it has been suggested that the results from this study will contribute to the present morphological knowledge on respiratory system and may shed light on the reconstructive anatomy and clinical procedures concerning this system.
... A laringe de Cerdocyon thous apresentou eixo longitudinal em continuidade horizontal com o corpo da mandíbula, o que é típico de mamíferos quadrúpedes (Saigusa 2011). De fato, a morfologia laríngea é marcadamente constante na classe Mammalia mesmo com as diferenças consideráveis entre porte corporal, padrão de fonação e estilo de vida das espécies (Harrison 1995). ...
Cerdocyon thous (crab-eating fox) is the most common wild canid in South American territory. The aim of this paper was to describe macroscopic, microscopic and comparative morphology of the larynx of this species. Analyses of larynges of sixteen specimens (four males and twelve females) revealed the topography, conformation, morphometrics, intrinsic muscles and histological characteristics. The larynx was positioned ventral to the axis and comprised one cricoid and one thyroid cartilage (hyaline), one epiglottis (elastic) and a pair of arytenoids (mixed). A pair of sesamoid cartilages was identified between the corniculate processes and the cricoid lamina. Morphometry revealed that thyroid cartilage was the largest. There were no conclusive signs of sexual dimorphism in the larynx of this species. Squamous stratified epithelium predominated and underwent transition to ciliated pseudo-stratified at the level of caudal thyroid and rostral cricoid portions. By comparison, larynx of C. thous showed similarity with the domestic dog, although the shape of cartilages has shown some variation.
... A laringe de Cerdocyon thous apresentou eixo longitudinal em continuidade horizontal com o corpo da mandíbula, o que é típico de mamíferos quadrúpedes (Saigusa 2011). De fato, a morfologia laríngea é marcadamente constante na classe Mammalia mesmo com as diferenças consideráveis entre porte corporal, padrão de fonação e estilo de vida das espécies (Harrison 1995). ...
Cerdocyon thous (crab-eating fox) is the most common wild canid in South American territory.
The aim of this paper was to describe macroscopic, microscopic and comparative morphology
of the larynx of this species. Analyses of larynges of sixteen specimens (four males
and twelve females) revealed the topography, conformation, morphometrics, intrinsic muscles
and histological characteristics. The larynx was positioned ventral to the axis and comprised
one cricoid and one thyroid cartilage (hyaline), one epiglottis (elastic) and a pair of arytenoids
(mixed). A pair of sesamoid cartilages was identified between the corniculate processes
and the cricoid lamina. Morphometry revealed that thyroid cartilage was the largest. There
were no conclusive signs of sexual dimorphism in the larynx of this species. Squamous stratified
epithelium predominated and underwent transition to ciliated pseudo-stratified at the
level of caudal thyroid and rostral cricoid portions. By comparison, larynx of C. thous showed
similarity with the domestic dog, although the shape of cartilages has shown some variation.
Objectives:
To distinguish the layers of the vocal fold at the submacroscopic level and determine their boundaries, thereby creating a basis for the construction of a digital 3D model of the human vocal folds.
Study design:
The submacroscopic delineation of individual layers of fixed vocal ligaments based on their structural differences.
Methods:
Following tasks were performed: (1) Submicroscopic dissection of the vocal folds fixed in a solution with a low concentration of fixation substance (in this case, the muscular parts of the vocal folds were removed); (2) Using the CT and micro-MRI methods, we determined the position of the dense parts of the vocal folds; and (3) Using a modified plastination method, we preserved macroscopically natural appearance of all ligamentous and muscular layers.
Results:
The vocal ligament is composed of several volumes of connective tissue. It is surrounded by layers of fibrous material permeated by liquid. Individual fibers stretch all the way to the fibrous casing (fascia) of the vocal muscle. The vocal fold layer surrounding the ligament externally has a stratified character.
Conclusions:
According to our findings, we infer that this ligament is a complex of several fibrous bundles which are surrounded by a thin layer of connective tissue. Below the surface of epithelium of the vocal fold run several separate bands which are closely adjacent to it. Therefore, we propose using the term ligamentous complex involving closely adjacent structures, instead of the vocal ligament only. We feel that it better reflects the functional and structural character of the whole formation.
The symptoms, endoscopic findings, treatment and results of 46 patients with laryngoceles and saccular cysts are presented. Thirty-four were adults; 12 were infants and children under three years of age. Twenty-two adults had anterior saccular cysts, nine had lateral saccular cysts; three had laryngoceles. Ten infants and children had saccular cysts; two had laryngoceles. A laryngocele is an abnormal dilatation of the saccule which communicates with the lumen of the larynx, fills with air but on occasion may be temporarily distended with mucus; laryngoceles may be congenital or acquired. A saccular cyst is a mucus-filled dilatation of the saccule which does not communicate with the laryngeal lumen; saccular cysts are classified as lateral or anterior. Laryngoceles and saccular cysts represent abnormalities of the laryngeal saccule; a developmental spectrum exists among the normal saccule, large saccule, laryngocele and saccular cyst. The treatment of saccular cysts in infants and children is primarily repeated aspiration. In adults, symptomatic laryngoceles and large lateral saccular cysts are treated by an external approach; endoscopic aspiration and unroofing of small lateral saccular cysts is sometimes adequate and is attempted first. Anterior saccular cysts are treated by endoscopic excision biopsy. Carcinoma of the larynx may be found in association with a laryngocele or saccular cyst and must be diligently searched for by biopsies in the region of the saccular orifice. A smooth mass involving the area of the false vocal cord and aryepiglottic fold cannot be assumed to be a lateral saccular cyst; biopsies of the ventricle and saccule and deep incisional biopsies of the mass are indicated to rule out a carcinoma originating in the ventricle or saccule.