The anatomy and internal architecture of the muscles of mastication in Didelphis marsupialis

The anatomy and internal architecture of the jaw musculature in Didelphis marsupialis, the American opossum, was studied using a combination of dissection and thick sectioning techniques. Since the purpose of this investigation was to provide detailed anatomical information as a basis for subsequent functional studies of jaw activity, all muscles associated with normal feeding and ancillary oral behaviour are described. These muscles are the temporal, masseter, pterygoids, digastric, mylohyoid, the remaining suprahyoid muscles and part of the extrinsic tongue musculature. In mammals, the jaw muscles medial to the superficial masseter are classically regarded as the temporal, masseter and zygomatico-mandibular; however, no structural justification for such a division can. be found in Didelphis. With the exception of the outermost layer of the adductor mass which is differentiated as a discrete superficial masseter, the temporal and masseteric part of the adductor musculature is a single unit converging from an extensive origin on bone and fascia to insert onto the coronoid process or its associated tendon. This musculature is described as consisting of three parts: an external adductor originating from the temporal fascia, the zygomatic arch and the masseteric fascia and inserting onto the external surface of the coronoid process, its tendon and the ramus of the lower jaw; an internal adductor originating primarily from the wall of the cranium and inserting onto the inner surface of the coronoid process; and a posterior adductor, the fibers of which pass anteriorly from the cranium posterior to the temporo-mandibular joint to insert onto the posterior border of the coronoid process and the most posterior part of its tendon. The fibers in each part have a different orientation but are not separated into discrete muscles. This division is for descriptive purposes only and no homologies are implied with the similarly named muscles of reptiles. The superficial masseter is a large, fan-shaped muscle extending from a tendinous origin on the maxilla to the inferior surface of the inflected mandibular angle where it has a thick, fleshy insertion. The remainder of the adductor musculature in the opossum consists of a very small external and a thick internal pterygoid muscle. The former inserts into the articular capsule of the temporo-mandibular joint as well as into the condylar neck. The latter has a long, almost linear cranial origin extending posteriorly from the palate toward the temporo-mandibular joint. The fibers pass inferolaterally to insert on the upper surface of the inflected angle. The anatomy of the suprahyoid muscles in the opossum is essentially the same as in eutherian mammals. All the muscles gain part, if not all, of their attachment to the hyoid through a thick, crescentic tendon formed by the fusion of the central tendons of both digastrics. No definite conclusions can be drawn as to the exact function of these muscles on the anatomical evidence alone. However, their position, internal architecture and relative size are suggestive: the external and internal adductors probably have the dual function of suspending the lower jaw from the cranium and adducting the jaw against resistance. The nearly horizontal orientation of much of the posterior adductor is evidence that it can, in addition, act as an effective retractor, with the superficial masseter as its antagonist. In addition to protracting the mandible, the superficial masseter may have a role in producing lateral movement in conjunction with the pterygoids or the adductors. Finally, the suprahyoid musculature in Didelphis probably functions, as in other mammals, to control the movement of the hyoid apparatus, the larynx and epiglottis, and the lower jaw relative to the hyoid. In addition, the mylohyoid, geniohyoid and genioglossus have an important action in elevating and depressing the floor of the mouth and the tongue

Tongue Movements in Feeding and Speech

The position of the tongue relative to the upper and lower jaws is regulated in part by the position of the hyoid bone, which, with the anterior and posterior suprahyoid muscles, controls the angulation and length of the floor of the mouth on which the tongue body \u27rides\u27. The instantaneous shape of the tongue is controlled by the \u27extrinsic muscles \u27 acting in concert with the \u27intrinsic \u27 muscles. Recent anatomical research in non-human mammals has shown that the intrinsic muscles can best be regarded as a \u27laminated segmental system \u27 with tightly packed layers of the \u27transverse\u27, \u27longitudinal\u27, and \u27vertical\u27 muscle fibers. Each segment receives separate innervation from branches of the hypoglosssal nerve. These new anatomical findings are contributing to the development of functional models of the tongue, many based on increasingly refined finite element modeling techniques. They also begin to explain the observed behavior of the jaw-hyoid-tongue complex, or the hyomandibular \u27kinetic chain\u27, in feeding and consecutive speech. Similarly, major efforts, involving many imaging techniques (cinefluorography, ultrasound, electro-palatography, NMRI, and others), have examined the spatial and temporal relationships of the tongue surface in sound production. The feeding literature shows localized tongue-surface change as the process progresses. The speech literature shows extensive change in tongue shape between classes of vowels and consonants. Although there is a fundamental dichotomy between the referential framework and the methodological approach to studies of the orofacial complex in feeding and speech, it is clear that many of the shapes adopted by the tongue in speaking are seen in feeding. It is suggested that the range of shapes used in feeding is the matrix for both behaviors

Fragmentation of a viscoelastic food by human mastication

Fragment-size distributions have been studied experimentally in masticated viscoelastic food (fish sausage).The mastication experiment in seven subjects was examined. We classified the obtained results into two groups, namely, a single lognormal distribution group and a lognormal distribution with exponential tail group. The facts suggest that the individual variability might affect the fragmentation pattern when the food sample has a much more complicated physical property. In particular, the latter result (lognormal distribution with exponential tail) indicates that the fragmentation pattern by human mastication for fish sausage is different from the fragmentation pattern for raw carrot shown in our previous study. The excellent data fitting by the lognormal distribution with exponential tail implies that the fragmentation process has a size-segregation-structure between large and small parts.In order to explain this structure, we propose a mastication model for fish sausage based on stochastic processes.Comment: JPSJ3, 4 pages, 8 figures, minor corrections made for publication in J. Phys. Soc. Jp

Overview of FEED, the Feeding Experiments End-user Database

The Feeding Experiments End-user Database (FEED) is a research tool developed by the Mammalian Feeding Working Group at the National Evolutionary Synthesis Center that permits synthetic, evolutionary analyses of the physiology of mammalian feeding. The tasks of the Working Group are to compile physiologic data sets into a uniform digital format stored at a central source, develop a standardized terminology for describing and organizing the data, and carry out a set of novel analyses using FEED. FEED contains raw physiologic data linked to extensive metadata. It serves as an archive for a large number of existing data sets and a repository for future data sets. The metadata are stored as text and images that describe experimental protocols, research subjects, and anatomical information. The metadata incorporate controlled vocabularies to allow consistent use of the terms used to describe and organize the physiologic data. The planned analyses address long-standing questions concerning the phylogenetic distribution of phenotypes involving muscle anatomy and feeding physiology among mammals, the presence and nature of motor pattern conservation in the mammalian feeding muscles, and the extent to which suckling constrains the evolution of feeding behavior in adult mammals. We expect FEED to be a growing digital archive that will facilitate new research into understanding the evolution of feeding anatomy

Oral processing of low water content foods: a development to Hutchings and Lillford’s breakdown path

The “hard to swallow” phenomenon previously reported for peanut paste has been investigated for other oil seed butters. The Temporal Dominance of Sensations (TDS) technique showed similar findings, adding to the list of materials which do not follow Hutchings and Lillford’s break down path (Journal of Texture Studies 19: 103-115). From our data we propose a modification to the Hutchings and Lillford model which allows for initial hydration of dry foods. The model holds well for oil seed pastes and may also help to explain the behaviour of some dry, carbohydrate rich, foods previously constrained to fit extant models. Since TDS does not measure the magnitude of an attribute, we undertook Time Intensity studies to assess stickiness of peanut pastes during oral processing. In the absence of another attribute becoming dominant, the intensity of sticky/cohesive sensations may remain paramount but diminish in intensity, prior to swallowing

Feeding in golden hamsters, Mesocricetus auratus

Simultaneous cine and electromyographic records of freely feeding, unanesthetized golden hamsters show that their motion and muscular activity during mastication differ from those of albino rats (Weijs, '75). Rats show only propalinal motion while hamsters show lateral translation as well. The masticatory muscles of hamsters and rats are generally similar, but their molar dentitions differ. The interlocking molar cusps of hamsters restrict propalinal protrusion and retrusion when the molars are in occlusion; however, hamsters readily unlock occlusion by a twisting movement in the horizontal plane. Rats may perform propalinal movements even with the teeth in occlusion. In mastication the hamstery's jaw moves laterally as well as vertically and anteroposteriorly. Chewing orbits typically reverse after one to three orbits. Reversal begins at the start of the upstroke and involves a lateral shift in the opposite direction with the mouth closed. Electromyograms show that symmetric and asymmetric activities of closing protrusive and closing retrusive muscles produce a unilateral force couple on both sides. (This couple accompanies a midline closing stroke.) When the mouth is closed, unilateral activity of closing retrusors and closing protrusors also induces lateral translation. A bilateral force couple pits the retrusors of one side against the protrusors on the opposite side. Simultaneous with lateral excursion to the opposite side of midline and the action of these closing muscles, the anterior digastric and lateral pterygoid muscles of one side fire asymmetrically. The mandible moves downward coincidently with bilateral activity of the digastrics and lateral pterygoids. As the jaw opens further, activity differences of the lateral pterygoids accompany a shift of the mandible toward midline. At the end of the downstroke, all masticatory muscles studied are silent. The jaw returns to midline when the adductors fire asymmetrically at the start of closing. Trituration appears to coincide with an initial simple protrusion, which is subsequently accompanied by lateral translation. Different food types are reduced by distint chewing patterns with the differences clearest when the teeth are near occlusion. During gnawing the lateral pterygoids and digastrics fire longer, and the closing muscles fire less strongly. Chewing patterns in golden hamsters appear more generalized than those of rats; the differences may be directly associated with the ability of hamsters to store food in their cheek pouches.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50269/1/1051540305_ftp.pd

Temporal dominance of sensations of peanuts and peanut products in relation to Hutchings and Lillford’s “breakdown path"

Hutchings and Lillford’s (Journal of Texture Studies, 19, 103-115, 1988) proposed a “breakdown path” whereby particle size reduction occurs through mastication in conjunction with the secretion of saliva to form a swallowable bolus. The swallowing trajectory of whole peanuts, peanut meal and peanut paste were studied with the temporal dominance of sensations technique. The sensations for whole peanuts progressed from hard, to crunchy, to chewy, to soft and ended compacted on teeth. Predictably peanut meal missed out the first two sensations, progressing from chewy, to soft and ending compacted on teeth. However peanut paste, which starts as a soft suspension with relatively little structure appears to thicken and stick to the palate during oral processing. We propose that the “hard to swallow” sensation elicited by peanut paste may be due to water absorption from the saliva as they mix in the mouth