Amount and spatial arrangement of muscle fibers in the human laryngeal Musculus 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.

Morphological and Histochemical Analysis of the Human Vestibular Fold / Análisis Morfológico e Histoquímico del Pliegue Vestibular Humano

A morphological and histochemical study of the human vestibular fold was carried out using routine histological techniques. Seven µm-thick histo logical sections stained with hematoxylin-eosin (HE) and Callej a showed the presence of elastic collagen fibers and seromucous glands in the vestibular fold. Muscle fibers forming the ventricular muscle were also identified. Ultrastructural analyses of the epithelial layer by scanning electron microscopy (SEM) revealed ciliated cells and gland ducts opening on the epithelial surface. Histochemical analyses were performed on ventricular muscles submitted to nicotinamide-adenine-dinucleotide tetrazolium reductase (NADH-TR), succinate dehydrogenase (SDH), and myofibrillar adenosine triphosphatase (mATPase) reactions. Based on these reactions, it was observed that the muscle is formed by three types of muscle fibers: slow-twitch oxidative (SO), fast-twitch oxydative glycolytic (FOG) and fast-twitch glycolytic (FG) fibers distributed in a mosaic pattern. The fiber frequency was 22.7%, 69.9% and 7.4%, respectively. The higher frequency of SO and FOG fibers characterized the muscle as having aerobic metabolism and resistance to fatigue. The ventricular muscle was considered fast. The study of the neuromuscular junctions performed after nonspecific esterase reaction showed that they are of the en-plaque type and have multiple occurrences in the ventricular muscle.

Fue realizado un estudio morfológico e histoquímico del pliegue vestibular humano a través de técnicas histológicas de rutina. Cortes histológicos de 7µm de grosor fueron teñidos con HE y Calleja, los cuales revelaron la presencia de fibras colágenas, elásticas y glándulas seromucosas en el pliegue vestibular. También fueron identificadas fibras musculares que constituyen el músculo ventricular. Los análisis ultraestruturales de la capa epitelial realizados a través de microscopía electrónica de barrido, mostraron la presencia de células ciliadas, caliciformes y abertura de conductos glandulares en la superficie epitelial. Los análisis histoquímicos fueron realizados con músculos ventriculares sometidos a las reacciones NADH-TR, SDH y mATPasa. En base en estas reacciones se observó que el músculo está constituido por tres tipos de fibras musculares SO, FOG y FG, distribuidas en la forma de mosaico. La frecuencia de las fibras fue de 22,7%, 69,9% e 7,4%, respectivamente. La mayor frecuencia de fibras oxidativas SO+FOG caracterizó al músculo, con metabolismo aeróbico, resistente a la fatiga. El músculo ventricular fue considerado como rápido. El estudio de las uniones neuromusculares, después de la reacción de la esterasa inespecífica, evidenció que estas uniones son del tipo placa y de ocurrencia múltiple en el músculo ventricular.