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.     

Fibre composition of human intrinsic tongue muscles

The muscle fibre composition of three human intrinsic tongue muscles, the longitudinalis, verticalis and transversus, was investigated in four anterior to posterior regions of the tongue using morphological and enzyme- and immunohistochemical techniques. All three muscles typically contained type I, IIA and IM/IIC fibres. Type I fibres expressed slow myosin heavy chain (MyHC), type II fibres fast MyHC, mainly fast A MyHC, whereas type IM/IIC coexpressed slow and fast MyHCs. Type II fibres were in the majority (60%), but regional differences in proportion and diameter of fibre types were obvious. The anterior region of the tongue contained a predominance of relatively small type II fibres (71%), in contrast to the posterior region which instead showed a majority of larger type I and type IM/IIC fibres (66%). In general, the fibre diameter was larger in the posterior region. This muscle fibre composition of the tongue differs from those of limb, orofacial and masticatory muscles, probably reflecting genotypic as well as phenotypic functional specialization in oral function. The predominance of type II fibres and the regional differences in fibre composition, together with intricate muscle structure, suggest generally fast and flexible actions in positioning and shaping the tongue, during vital tasks such as mastication, swallowing, respiration and speech.     

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.     

Reflex control of cat extrinsic and intrinsic tongue muscles exerted by intraoral receptors

The effects of mechanical and noxious stimulation of the palatal and lingual surfaces on the activity of the extrinsic and intrinsic tongue muscles have been studied in cats. Stimulation of the hard palate produced mainly activation of extrinsic tongue muscles while inhibition was elicited by stimulating the soft palate. Longlasting pressure on the hard palate caused rhythmic tongue flapping by intermittent genioglossal activity. The intrinsic tongue muscles, m. transversus and m. verticalis, were activated by noxious stimuli applied to the hard palate, the effects apparently being mediated by high-threshold afferents. Mechanical and noxious stimulation applied to the dorsal and ventral lingual surfaces of the tongue either activated or inhibited the extrinsic tongue muscles depending on the reflex area stimulated. The intrinsic tongue muscles were activated by noxious stimuli applied to the tongue surfaces. The anastomoses running between the hypoglossal and lingual nerves were found to mediate mainly nociceptive afferent impulses travelling from the hypoglossal to the lingual nerve. The intrinsic muscles were found to be controlled by anastomosal nociceptive afferents.     

Three-dimensional architecture of the connective tissue papillae of the mouse tongue as viewed by scanning electron microscopy

The morphological relationship between lingual papillae and underlying connective tissue papillae of mouse was studied because it is conceivable that the differentiation of epithelium may be affected by its connective tissue. Tongues of adult male mice were fixed in formol or Karnovsky's fixative. After removal of the epithelium by long-term hydrochloric acid treatment at room temperature, the surface of the connective tissue papillae was observed by scanning electron microscopy. Connective tissue papillae that were fungiform in shape and which were distributed at the anterior part of the tongue showed barnacle-like protrusion after removal of the epithelium. Their surface was covered by numerous long filaments running vertically and there was a round depression on the top of each fungiform papilla that may be found to correspond to a taste bud when the results of light and electron microscopy are compared. Filiform papillae in a narrow sense were closely distributed in the anterior part of the tongue. They had a tapered tip declining posteriorly. Each filiform connective tissue papilla was conical in shape and had a round depression that slightly declined antero-downward, and a long narrow depression ran along the anterior edge of each connective tissue papilla. Large conical papillae which distributed at the anterior margin of the intermolar prominence had shovel-like connective tissue papillae which had a depression at the posterior surface unlike that of the filiform papillae. Branched papillae distributed in the posterior part of the prominence had a depression at the anterior surface. Under the light microscope, numerous keratohyaline granules were seen to be contained only in the posterior epithelial cell line of the large conical papillae distributed in the anterior margin of the prominence, while these granules were found only in the anterior epithelial cell line of both filiform and branched papillae. It became clear that the axes of each connective tissue papilla of large conical papillae distributed radically around a single midpoint. Connective tissue papillae of vallate papillae had a beehive-like shape and in follicate papillae there were several vertical elliptical gaps, seen when the epithelium was peeled from the connective tissue.     

Reflex tone in the tongue muscles

Summary The tonus of the tongue muscles was studied in animals. Experiments were performed on anesthetized cats. The tongue was stretched with weights ranging from 20 to 30 g. Reaction of the tongue to stretching was registered by a cathode ray oscillograph. It was established that the more the tongue is stretched, the greater its electric activity i. e. the more pronounced the proprioceptive reflex of stretching. Section of hypoglossal nerves destroys the tonus of the tongue muscles at rest, as well as proprioceptives reflexes to stretching.Presented by Active Member of the Academy of Medical Sciences, USSR, A. F. Tur     

Contraction times of the cat's tongue muscles measured by light reflection. Innervation of individual tongue muscles

The contraction times of the cat's tongue muscles were measured by recording the fine movements of their surfaces and movements of the tongue's surfaces. The recordings were made by means of a commercial, high-sensitive light reflection transducer (Fairchild FPLA 850) which could be operated without any mechanical loading of the tongue. The contraction times of the intrinsic muscles (including pars longitudinalis superior m. hypoglossi and pars longitudinalis inferior m. styloglossi) measured about 22 ms, while the extrinsic muscles were somewhat slower, around 33 ms. The data are considered in the light of the recently reported histochemical composition of these muscles. The study of the hyoglossal nerve supply to individual tongue muscles revealed that, contrary to earlier reports, the medial nerve sends branches to the intrinsic muscles not only at its distal end but during its entire course through the tongue. The transversal and vertical muscles were found to receive numerous fibers innervating small units of their muscle fibers.     

Origin and development of the avian tongue muscles

 The musculature of the vertebrate tongue is composed of cells recruited from the somites. In this paper we have investigated the migration and organisation of the muscle cells that give rise to the tongue muscle during chick embryogenesis. At the molecular level, our data suggests that a population of Tbx-3 expressing cells migrate away from the occipital somites prior to the migration of muscle precursors that express Pax-3. Both populations take the same pathway and form the hypoglossal cord. The first signs of muscle cell differentiation were not detected until cells had migrated some distance from the somites. We have determined the contribution of single somites to the musculature of the tongue and show in contrast to previous data that somites 2–6 take part in the formation of all glossal and infrahyoid muscles to the same extent but do not contribute to suprahyoid muscle. This is particularly interesting since glossal and infrahyoid muscle differ from the suprahyoid muscles not only in their morphology, but also in their developmental origin. Furthermore we show that myocytes cross the midline and contribute to the contralateral glossal and infrahyoid muscles. This is supported from our molecular data, which showed that the migratory precursor population was maintained primarily at the rostral tip of the developing hypoglossal cord. Accepted: 15 February 1999     

舌血管构筑及计量学研究

目的：通过对舌血管的观察和计量，为舌下络脉诊，舌瓣提供形态学依据。方法：墨汁灌注，用手术放大镜、显微镜观察人舌血管的构筑，并用Ｑｕａｎｔｉｍｅｔ５２０＋型图像分析仪对舌各种乳头，舌粘膜肌层、舌肌的血管进行计量学研究。结果：单位面积内轮廓乳头的血管密度大于菌状和丝状乳头；舌肌的血管也明显丰富于舌粘膜肌层。结论：舌静脉的回流主要通过舌下神经伴行静脉，该静脉也是舌下络脉诊主要观察的对象。舌粘膜两侧血管吻合丰富，用舌粘膜肌瓣修复扁桃体窝，磨牙后区等特定的解剖部位有其他瓣无法代替的优点。     

Quantitative analysis of the intrinsic muscles of the hand

As part of a study involving three-dimensional modeling of the hand, the intrinsic muscles of the hand were evaluated quantitatively to estimate the range of muscular forces crossing the fingers. The Brand method of dissection allowed determination of muscle volume, fiber length, and physiologic cross section to estimate the maximal force. The intrinsic muscles were grouped by components on the basis of their origins in the trilaminar scheme of Cunningham as (1) dorsal abductors from the central ray, exemplified by the bipennate dorsal interossei; (2) the intermediate layer consisting of inter-phalangeal joint extensors, exemplified by the unipennate palmar interossei with insertions into the extensor expansion; and (3) a superficial layer of adductors arising from the third metacarpal ridge, referred to as contrahentes. The fiber lengths of either component of the dorsal interossei averaged 1.3 cm. The intermediate layer of muscle, numbered as flexores breves (FB), included the palmar interossei FB_4,7,9; the superficial components of the dorsal interossei FB_3,5,6,8; and the accessory adductor pollicis FB₂. Fiber lengths averaged 1.7 cm. The superficial heads of the flexor pollicis brevis and abductor digiti quinti are possibly the border representations of the intermediate layer as FB₁ and FB₁₀. The thenar muscles made up 37%, dorsal interossei 24%, palmar interossei (flexores breves) of the fingers 16%, lumbricals 7%, and hypothenar muscles 16% of the total intrinsic muscle mass. The ratio of muscle mass to fiber length, the physiologic cross-sectional area, is useful in estimating available force. This quantitative analysis of the intrinsic musculature may find application in the understanding of hand function and biomechanics.     

Three-dimensional architecture of the left ventricular myocardium

Concepts for ventricular function tend to assume that the majority of the myocardial cells are aligned with their long axes parallel to the epicardial ventricular surface. We aimed to validate the existence of aggregates of myocardial cells orientated with their long axis intruding obliquely between the ventricular epicardial and endocardial surfaces and to quantitate their amount and angulation. To compensate for the changing angle of the long axis of the myocytes relative to the equatorial plane of the ventricles with varying depths within the ventricular walls, the so-called helical angle, we used pairs of cylindrical knives of different diameters to punch semicircular slices from the left ventricular wall of pigs, the slices extending from the epicardium to the endocardium. The slices were pinned flat, fixed in formaldehyde, embedded in paraffin, sectioned, stained with azan or hematoxilin and eosin, and analyzed by a new semiautomatic procedure. We made use of new techniques in informatics to determine the number and angulation of the aggregates of myocardial cells cut in their long axis. The alignment of the myocytes cut longitudinally varied markedly between the epicardium and the endocardium. Populations of myocytes, arranged in strands, diverge by varying angles from the epicardial surface. When paired knives of decreasing diameter were used to cut the slices, the inclination of the diagonal created by the arrays increases, while the lengths of the array of cells cut axially decreases. The visualization of the size, shape, and alignment of the myocytic arrays at any side of the ventricular wall is determined by the radius of the knives used, the range of helical angles subtended by the alignment of the myocytes throughout the thickness of the wall, and their angulation relative to the epicardial surface. Far from the majority of the ventricular myocytes being aligned at angles more or less tangential to the epicardial lining, we found that three-fifths of the myocardial cells had their long axes diverging at angles between 7.5 and 37.5 degrees from an alignment parallel to the epicardium. This arrangement, with the individual myocytes supported by connective tissue, might control the cyclic rearrangement of the myocardial fibers. This could serve as an important control of both ventricular mural thickening and intracavitary shape.     

Reinnervation of motor units in intrinsic muscles of a transplanted hand

Functional recovery of transplanted hand can be evaluated clinically but until now there has been no direct assessment of muscle control. In October 2000 we transplanted the right hand of a brain-dead man aged 43 onto a man aged 35 who had lost his right dominant hand 22 years before. Starting from day 205 after the transplant, multi-channel surface electromyographic (EMG) signals were recorded from intrinsic muscles of the transplanted hand in order to assess their degree of reinnervation. Eleven months post-operatively, the first motor unit action potential train was detected from the abductor digiti minimi. One month later, also the abductor pollicis brevis and the opponens pollicis muscles showed motor unit activity, while, after 15 and 24 months, the first dorsal interosseous and the first lumbricalis muscles, respectively, showed activation of their first motor units. An increase in the number of active motor units was observed after the first signs of reinnervation, although the process was rather slow. In sustained maximal contractions, the motor unit discharge rate decreased from (mean +/- S.D.) 34.0+/-6.7 pps to 23.4+/-5.1 pps in 60 s for the abductor digiti minimi, although the subject was verbally encouraged to maintain a maximal activation. Moreover, the subject was able to perform basic control tasks involving voluntary modulation of motor unit discharge rate. With a visual feedback, he could increase discharge rate of the abductor digiti minimi approximately linearly over time, from 13.4+/-6.7 pps to 32.5+/-11.2 pps in 60 s. In conclusion, we showed reinnervation of single motor units in a transplanted hand after 22 years of denervation. Moreover, voluntary modulation of discharge rates of these motor units could be performed since the first sign of reinnervation.     

Estimation of the number and size of motor units in intrinsic laryngeal muscles using morphometric methods

The number and size of motor units in the intrinsic laryngeal muscles were estimated by morphometric methods. Laryngeal muscles with their respective nerve branches were obtained from 64 fresh cadavers (32 older than 60 years, mean age 74 +/- 9 years and 32 younger than 60 years, mean age 51 +/- 8 years). Myelinated nerve fibers and the total number of muscle fibers were counted. Motor unit size was estimated by dividing the total number of muscle fibers by the total number of motor units in each case. The mean number of motor units ranged from 268 +/- 1.3 (interarytenoid muscle) to 431 +/- 1.6 (cricothyroid muscle). Thyroarytenoid and cricothyroid muscle presented the smallest (9.8 +/- 0.2) and largest (20.5 +/- 0.9) motor unit size, respectively, suggesting that thyroarytenoid muscle has a greater capacity to fine-tune its total force compared with the other intrinsic laryngeal muscles. No differences in motor unit number or size were observed between the right and left sides or between younger and older subjects. It is suggested that synaptic rearrangements may occur at the level of the neuromuscular junction in the human larynx that may explain the age-related changes in motor units reported by clinical methods.     

Collagen fibrils in the odontoblast layer of the rat incisor by scanning electron microscopy using the maceration method

Background: There is not universal agreement on the existence of the extracellular pathway from the pulp along the odontoblast layer to the predentin. Method: To confirm this pathway, the architecture of collagen fibrils in the rat incisor dentin and pulp, especially in the odontoblast layer of the lateral (periodontal ligament) sides of the tooth, was demonstrated in the present investigation using scanning electron microscopy of the maceration method for collagen networks. Results: Numerous collagen bundles were observed in the odontoblast layer in the mature odontoblast region which, except for the young odontoblast region, comprises the major portion of the incisor. The collagen bundles went from the pulp, through the odontoblast layer, and were woven into the collagen network of the predentin. The meshwork structure was composed of fine secondary fibrils among these collagen bundles. The surface of the predentin contained many oval-shaped holes which were surrounded by collagen fibrils. Fracturing the dentin longitudinally relative to the dentinal tubules revealed that the arrangement of the collagen fibrils at the surface of the tubules was either circular or oblique. In the young odontoblast region, i.e., the thin portion from the apical end of the incisor where the mineralization of the dentin does not occur and where the height of the odontoblasts was less than 30 μm, many thick bundles composed of thick collagen fibrils ran straight from the pulp to the predentin through the odontoblast layer and fanned out into the collagen network of the predentin. These thick bundles might correspond to the so-called “von Korff fibers.” The distribution of collagen fibrils in the pulp was random except on the surface of the blood vessels where the fibrils comprised two sheets of collagen: the inner sheet which coursed longitudinally to the long axis of the vessel, and the outer sheet which ran transversely. Conclusion: It was considered that the fluid in the pulp could flow to the predentin along the collagen fibrils through the tight junction between the odontoblasts. © 1994 Wiley-Liss, Inc.     

Functional anatomy of the hypoglossal innervated muscles of the rat tongue: a model for elongation and protrusion of the mammalian tongue

This anatomical investigation in the rat was designed to illustrate the detailed organization of the tongue's muscles and their innervation in order to elucidate the actions of the muscles of the higher mammalian tongue and thereby clarify the protrusor subdivision of the hypoglossal-tongue complex. The hypoglossal innervated, extrinsic styloglossus, hyoglossus, and genioglossus and the intrinsic transversus, verticalis and longitudinalis linguae muscles were observed by microdissection and analysis of serial transverse-sections of the tongue. Sihler's staining technique was applied to whole rat tongues to demonstrate the hypoglossal nerve branching patterns. Dissections of the tongue demonstrate the angles at which the extrinsic muscles act on the base of the tongue. The Sihler stained hypoglossal nerves demonstrate branches to the styloglossus and hyoglossus emanating from its lateral division while branches to the genioglossus muscle exit from its medial division. The largest portions of both XIIth nerve divisions can be seen to enter the body of the tongue to innervate the intrinsic muscles. Transverse sections of the tongue demonstrate the organization of the intrinsic muscle fibers of the tongue. Longitudinal muscle fibers run along the entire circumference of the tongue. Alternating sheets of transverse lingual and vertical lingual muscles can be observed to insert into the circumference of the tongue. Most importantly in clarifying tongue protrusion, we demonstrate the transversus muscle fibers enveloping the most superior and inferior portions of the longitudinalis muscles. Longitudinal muscle fascicles are completely encircled and thus are likely to be compressed by transverse muscle fascicles resulting in elongation of the tongue. We discuss our findings in relation to biomechanical studies, that describe the tongue as a muscular hydrostat and thereby define the "elongation-protrusion apparatus" of the mammalian tongue. In so doing, we clarify the functional organization of the hypoglossal-tongue complex.