Respiratory function of hyoid muscles and hyoid arch

The position of the hyoid arch suggests that it supports soft tissue surrounding the upper airway (UA) and can act to maintain UA patency. We also suspected that muscles inserting on the hyoid arch might show respiratory patterns of activity that could be affected by respiratory stimuli. To test these possibilities, we moved the hyoid arch ventrally in six anesthetized dogs either by traction on it or by stimulation of hyoid muscles. UA resistance was decreased 73 +/- (SE) 6% and 72 +/- 6% by traction and stimulation during expiration and 57 +/- 15% and 52 +/- 8% during inspiration. Moving averages of the geniohyoid (GH) and thyrohyoid (TH) obtained in six other dogs breathing 100% O2 showed phasic respiratory activity while the sternohyoid (SH) showed phasic respiratory activity in only two of these animals and no activity in four. With progressive hypercapnia, GH and TH increased as did SH when activity was already present. Airway occlusion at end expiration augmented and prolonged inspiratory activity in the hyoid muscles but did not elicit SH activity if not already present. Occlusion at end inspiration suppressed phasic activity in hyoid muscles for as long as in the diaphragm. After vagotomy activity increased and became almost exclusively inspiratory. Activity appeared in SH when not previously present. Duration and amplitude of hyoid muscle activity were increased with negative UA pressure and augmented breaths. We conclude that the hyoid arch and muscles can strongly affect UA flow resistance. Hyoid muscles show responses to chemical, vagal, and negative pressure stimuli similar to other UA muscles.     

Development of the mandibular, hyoid arch and gill arch skeleton in the Chinese barb Puntius semifasciolatus: comparisons of ossification sequences among Cypriniformes

The morphogenesis and sequence of ossification and chondrification of skeletal elements of the jaws, and hyoid arch and gill arches of Puntius semifasciolatus are described. These data provide a baseline for further studies and enable comparisons with other described cypriniforms. Some general patterns of ossification in the hyoid arch and branchial arches in cypriniforms were notable. First, the overall development is from anterior to posterior, with the exception of the fifth ceratobranchial bone, which ossifies first. Second, where ossification of iterated elements is sequential, it tends to proceed from posterior to anterior, even when more posterior chondrifications are the smallest in the series. Ossification of the ceratobranchial, epibranchial and pharyngobranchial bones tends to proceed from ventral to dorsal. The comparisons revealed small sets of skeletal elements whose ossification sequence appears to be relatively conserved across cyprinid cypriniforms. Several potentially key timing changes in the ossification sequence of the jaws, hyoid arch and gill arches were identified, such as the accelerated timing of ossification of the fifth ceratobranchial bone, which may be unique to cypriniforms.     

The hyoid complex of Rattus rattus rufescens

The hyoid apparatus of the rat consists of an anteroposterior compressed and somewhat arched basihyal, the small anterior cornua and the more prominent posterior cornua. The ceratohyal is the only movably articulated element of the anterior cornu and is generally lost during the normal methods of preparing skeleton. The absence of stylohyal has resulted in modifications in the origins and insertions of Mm. stylohyoideus, styloglossus, and stylopharyngeus. The study of the hyoid region of rats, gerbils and squirrels supports the view that the muroid rodents have originated from the more generalized squirrel-like forms.     

Feeding of the megamouth shark (Pisces: Lamniformes: Megachasmidae) predicted by its hyoid arch: A biomechanical approach

Studies of the megamouth shark, one of three planktivorous sharks, can provide information about their evolutionary history. Megamouth shark feeding has never been observed in life animals, but two alternative hypotheses on biomechanics suggest either feeding, i.e., ram feeding or suction feeding. In this study, the second moment of area of the ceratohyal cartilages, which is an indicator of the flexural stiffness of the cartilages, is calculated for 21 species of ram‐ and suction‐feeding sharks using computed tomography. The results indicate that suction‐feeding sharks have ceratohyal cartilages with a larger second moment of area than ram‐feeding sharks. The result also indicates that the ram–suction index, which is an indicator of relative contribution of ram and suction behavior, is also correlated with the second moment of area of the ceratohyal. Considering that large bending stresses are expected to be applied to the ceratohyal cartilage during suction, the larger second moment of area of the ceratohyal of suction‐feeding sharks can be interpreted as an adaptation for suction feeding. Based on the small second moment of area of the ceratohyal cartilage of the megamouth shark, the feeding mode of the megamouth shark is considered to be ram feeding, similar to the planktivorous basking shark. From these results, an evolutionary scenario of feeding mechanics of three species of planktivorous sharks can be suggested. In this scenario, the planktivorous whale shark evolved ram feeding from a benthic suction‐feeding ancestor. Ram feeding in the planktivorous megamouth shark and the basking shark evolved from ram feeding swimming‐type ancestors and that both developed their unique filtering system to capture small‐sized prey. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Developmental patterns of the crocodilian and avian columella auris: reappraisal of interpretations of the derivation of the dorsal hyoid arch in archosaurian tetrapods

The morphogenesis of the crocodilian and avian columella auris is analysed, using Alligator and Struthio as models that are studied in detail, and Crocodylus, Gallus, and Coturnix as models for comparative purposes. This investigation was undertaken to address controversies emanating from previous studies concerning the identity of archosaurian hyal elements, and to clarify confounding nomenclature that has been used for both topographic and phylogenetic purposes. We found that confusion in the identification of the reptilian and avian hyoid arch derivatives is attributable to: (1) redundant and/or inconsistently applied topographical terminology; (2) mixing of topographical and phylogenetic terminology; (3) interpretation in a recapitulatory framework; and (4) failure to consider that developmental pathways of recent archosaurians (reptilians and birds) might be divergently modified. Our analysis identifies errors in previous interpretations, misinterpretations of prior work, and histological observations that have been idealized. The most controversial issues are addressed – the derivation of the supracolumellar process; the concept of the laterohyal component; and segmentation of the distal part of the reptilian and avian columella auris. Based on new data, we suggest that the osteichthyan infrapharyngohyal, suprapharyngohyal, epihyal, and ceratohyal are not applicable terms for reptilian and avian columellar components from a phylogenetic perspective, and should not be used as topographical terms either. We further propose that the original morphogenetic program of the hyoid arch has been overwritten in newly derived evolutionary pathways of crocodilians and birds, in which a new functional and morphological patterning of the hyoid arch, as a specific sound‐transmitting apparatus, have evolved. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 384–410.     

The control of multi-muscle systems: human jaw and hyoid movements

A model is presented of sagittal plane jaw and hyoid motion based on the model of motor control. The model, which is implemented as a computer simulation, includes central neural control signals, position- and velocity-dependent reflexes, reflex delays, and muscle properties such as the dependence of force on muscle length and velocity. The model has seven muscles (or muscle groups) attached to the jaw and hyoid as well as separate jaw and hyoid bone dynamics. According to the model, movements result from changes in neurophysiological control variables which shift the equilibrium state of the motor system. One such control variable is an independent change in the membrane potential of -motoneurons (MNs); this variable establishes a threshold muscle length () at which MN recruitment begins. Motor functions may be specified by various combinations of s. One combination of s is associated with the level of coactivation of muscles. Others are associated with motions in specific degrees of freedom. Using the model, we study the mapping between control variables specified at the level of degrees of freedom and control variables corresponding to individual muscles. We demonstrate that commands can be defined involving linear combinations of change which produce essentially independent movements in each of the four kinematic degrees of freedom represented in the model (jaw orientation, jaw position, vertical and horizontal hyoid position). These linear combinations are represented by vectors in space which may be scaled in magnitude. The vector directions are constant over the jaw/hyoid workspace and result in essentially the same motion from any workspace position. The demonstration that it is not necessary to adjust control signals to produce the same movements in different parts of the workspace supports the idea that the nervous system need not take explicit account of musculo-skeletal geometry in planning movements.This article was processed by the author using the LAT_EX style file pljour2 from Springer-Verlag.     

The British dental arch

Thirty-two dimensions of the maxillary and mandibular dental arches were measured on 320 adult skulls derived from Anglo-saxon to modern times. Multivariate analysis showed varying patterns of contrast between the samples, depending upon which arch dimensions were considered. The results suggest that dental arch changes occur independently of jaw changes.     

The evolution of hyoid apparatus in Xenarthra (Mammalia: Eutheria)

The hyoid apparatus reflects aspects of the form and function of feeding in living and extinct organisms and, despite the availability of information about this structure for Xenarthra, it remains little explored from an evolutionary perspective. Here we compare the morphology of the hyoid apparatus in xenarthrans, describing its general morphology and variation in each major clade and score these variations as phylogenetic characters, which were submitted to ancestral states reconstructions. The general hyoid morphology of Xenarthra consists of a v-bone (basihyal fused with the thyrohyals) and three paired bones (stylohyal, epihyal and ceratohyal), which are unfused in the majority of taxa. The clade-specific morphology observed here, allowed us to obtain additional synapomorphies for all major clades of Xenarthra (Cingulata, Pilosa, Folivora and Vermilingua), for Glyptodontididae, and for Nothrotheriidae. The fusion of hyoid elements are convergentelly achieved among the diphyletic extant tree sloths, some extinct ground sloths and glyptodontids. Despite the heavy influence of adaptive evolution related to feeding habits, the morphology of the hyoid apparatus proved to be a valuable source of phylogenetic information.     

Determination of sex from the hyoid bone

This article explores size differences related to sex in the hyoid bones from the Robert J. Terry Anatomical Collection. A series of measurements were taken from 398 hyoids, both fused and unfused. The inclusion of unfused hyoids in the study provides the opportunity to investigate previously unknown size differences between sexes as well as to determine their utility in determining sex. Two‐way ANOVA was used to explore differences in hyoid size as related to ancestry and sex. Discriminant function analysis was employed to test the ability of the hyoids to be classified by sex. Six discriminant function equations ranging in accuracy from 82% to 85% are provided, each of which is more accurate than many of the discriminant functions developed in past hyoid research, are simple to use, and can be used to estimate the sex of a hyoid regardless of its state of fusion. In addition to providing further information about the morphological form of the hyoid, these analyses provide a method that can be easily employed to assess sex of the individual from the hyoid bone. Am J Phys Anthropol 143:279–284, 2010. © 2010 Wiley‐Liss, Inc.     

Sagittal plane kinematics of the adult hyoid bone

The hyoid bone is a unique bone in the skeleton not articulated to any other bone. The hyoid muscles, which attach to the hyoid bone, may play a role in neck mechanics, but analysis of their function requires quantifying hyoid bone mechanics. The goal of this study was to obtain the detailed kinematics of the hyoid bone over a large range of flexion-extension motion using radiographs at 5 postures. The position of the hyoid bone in the sagittal plane was characterized with respect to head, jaw, and vertebral movements. Sex differences in hyoid kinematics were also investigated. We hypothesized that (1) the position of the hyoid bone in the sagittal plane is linearly correlated with motion of the head, jaw, and vertebrae, and (2) the hyoid position, size, and kinematics are sex-specific. We found that the hyoid bone X, Y, and angular position generally had strong linear correlations with the positions of the head, jaw, and the cervical vertebrae C1-C4. Hyoid X and angular position was also correlated to C5. Sex differences were found in some regressions of the hyoid bone with respect to C1-C5. The angular and linear measurements of the hyoid bone showed sex differences in absolute values, which were not evident after normalization by posture or neck size. Incorporating these results to neck models would enable accurate modeling of the hyoid muscles. This may have implications for analyzing the mechanics of the cervical spine, including loads on neck structures and implants.     

Movement of the hyoid in frogs during feeding.

Feeding, breathing, and vocalization sequences of Bufo marinus were recorded by cineradiography. Results of film analysis indicate that the hyoid moves during all three behaviors. Movement of the hyoid is critical in tongue protrusion of frogs, and a biomechanical model of this action is presented. The hyoid appears to represent a compromise morphological system for three functions, rather than an optimal system for any one. This may explain, in part, the retention of a relatively inefficient breathing mechanism in frogs.     

The gut flagellate community of the termite Neotermes cubanus with special reference to Staurojoenina and Trichocovina hrdyi nov. gen. nov. sp

At least seven species of flagellates have been found to inhabit the paunch of the termite Neotermes cubanus. Staurojoenina sp. is the largest species, measuring 100-150mum in length. Three small parabasalids belong to the genera Tritrichomonas, Metadevescovina, and Foaina. A fourth small type is described as Trichocovina hrdyi nov. gen. nov. sp.; the combination of features in this flagellate, such as the presence of a costa, undulating membrane and spiralled dictyosome, does not fit to any known genus. The two oxymonad species do not possess a rostellum. One belongs to the family Polymastigidae; it has one unattached flagellum and three partially attached flagella. The second is a member of the family Pyrsonymphidae, but this one possesses ring-like surface structures, one free flagellum and three spirally attached flagella. It is the first report of a pyrsonymphid in a kalotermitid termite.     

EMG activity in hyoid muscles during pig suckling

Infant suckling is a complex behavior that includes cycles of rhythmic sucking as well as intermittent swallows. This behavior has three cycle types: 1) suck cycles, when milk is obtained from the teat and moved posteriorly into the valleculae in the oropharynx; 2) suck-swallow cycles, which include both a rhythmic suck and a pharyngeal swallow, where milk is moved out of the valleculae, past the larynx, and into the esophagus; and 3) postswallow suck cycles, immediately following the suck-swallow cycles. Because muscles controlling these behaviors are active in all three types of cycles, we tested the hypothesis that different patterns of electromyographic (EMG) activity in the mylohyoid, hyoglossus, stylohyoid, and thyrohyoid muscles of the pig characterized each cycle type. Anterior mylohyoid EMG activity occurred regularly in every cycle and was used as a cycle marker. Thyrohyoid activity, indicating the pharyngeal swallow, was immediately preceded by increased stylohyoid and hyoglossus activity; it divided the suck-swallow cycle into two phases. Timed from the onset of the suck-swallow cycle, the first phase had a relatively fixed duration while the duration of the second phase, timed from the thyrohyoid, varied directly with cycle duration. In short-duration cycles, the second phase could have a zero duration so that thyrohyoid activity extended into the postswallow cycle. In such cycles, all swallowing activity that occurred after the thyrohyoid EMG and was associated with bolus passage through the pharynx fell into the postswallow cycle. These data suggest that while the activity of some muscles, innervated by trigeminal and cervical plexus nerves, may be time locked to the cycle onset in swallowing, the cycle period itself is not. The postswallow cycle consequently contains variable amounts of pharyngeal swallowing EMG activity. The results exemplify the complexity of the relationship between rhythmic sucking and the swallow.     

The relationship of dental crowding to tooth size, dental arch width, and arch depth

This study was undertaken to answer the question, "Are there any differences in the mesiodistal tooth diameters, dental arch width and dental arch depth between the crowded and noncrowded dentitions?" The materials submitted for study consisted of the Orthoscan intraoral occlusograms of 89 subjects with well-aligned dentition and those of 74 subjects with gross dental crowding. The tooth size and arch dimensions were measured from these intraoral occlusograms. The data were subjected to statistical treatment for comparison of noncrowded and crowded groups. The findings in this study lead to the following conclusions: The mesiodistal tooth diameters of the crowded group were significantly larger than those of the noncrowded group. The dental arch widths of the crowded group were significantly smaller than those of the noncrowded group. No substantial or significant difference in dental arch depth between the crowded and noncrowded subjects could be noted. From these findings it seems that tooth size and dental arch width are determining factors in the formation of dental crowding. Clinically, these results suggest that in the treatment of dental crowding, extraction of teeth and/or expansion of dental arches should be considered depending on what is the main causative factor.     

Mechanical function of hyoid muscles during spontaneous breathing in cats

We assessed the mechanical behavior of the geniohyoid and sternohyoid muscles during spontaneous breathing using sonomicrometry in anesthetized cats. When the animals breathed O2, the hyoid muscles either became longer or did not change length (but never shortened) during inspiration. During progressive hyperoxic hypercapnia, transient increases in geniohyoid muscle inspiratory lengthening occurred in many animals; however, at high PCO2 the geniohyoid invariably shortened during inspiration (mean 4.9% of resting length at the end of CO2 rebreathing; P less than 0.001). The PCO2 at which geniohyoid inspiratory lengthening changed to inspiratory shortening was significantly higher than the CO2 threshold for the onset of geniohyoid electrical activity (P less than 0.01). For the sternohyoid muscle, hypercapnia caused inspiratory lengthening in 13 of 17 cats and inspiratory shortening in 4 of 17 cats; on average the sternohyoid lengthened by 1.6% of resting length at the end of CO2 rebreathing (P less than 0.01). Sternohyoid lengthening occurred in spite of this muscle being electrically active. These results suggest that the relationship between hyoid muscle electrical activity and respiratory changes in length is very complex, so that the presence of hyoid muscle electrical activity does not necessarily indicate muscle shortening, and among the geniohyoid and sternohyoid muscles, the geniohyoid has a primary role as a hypopharyngeal dilator in the spontaneously breathing cat, with the sternohyoid muscle acting in an accessory capacity.