The twitch-contraction characteristics of opossum jaw musculature

doi:10.1016/0003-9969(75)90046-1

Archives of Oral Biology

Volume 20, Issue 11, November 1975, Pages 743-748

https://doi.org/10.1016/0003-9969(75)90046-1 Get rights and content

Abstract

The characteristics of twitch contractions in the masticatory muscles of the American opossum were investigated in situ. The mean time to peak contraction in Temporalis was 18.3 msec, in Masseter—15.8 msec, in Medial Pterygoid—15.9 msec and in Anterior Digastric-11.1 msec. The length-tension relationship (length expressed as a jaw position) was highly characteristic for each elevator muscle. The maximum twitch tension was produced at different jaw positions in each case: Temporalis at 33 ° open, Masseter at 29 ° and Medial Pterygoid at 20 ° open. Hysteresis was present, however, in the length-tension relationship.

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Cited by (41)

Functional correlates of the position of the axis of rotation of the mandible during chewing in non-human primates
2017, Zoology
Citation Excerpt :
Carlson’s conclusions were partially supported by a study that evaluated the effect of different locations of the mandibular AoR on the torque-generating capacity of the jaw-elevator muscles in rabbits (Weijs et al., 1989). In this study the authors argued that in many animals, including humans, optimal sarcomere length occurs at gapes larger than minimum gape, i.e., centric occlusion (Nordstrom et al., 1974; Nordstrom and Yemm, 1974; Thexton and Hiiemae, 1975; Anapol and Herring, 1989), so that some degree of jaw depression brings the masseter to the peak of its length–tension curve. Nonetheless, as in Carlson’s study, Weijs et al. (1989) found the location of the AoR minimizes muscle stretch of both masseter and medial pterygoid, mitigating the reduction in active force generation.
The location of the axis of rotation (AoR) of the mandible was quantified using the helical axis (HA) in eight individuals from three species of non-human primates: Papio anubis, Cebus apella, and Macaca mulatta. These data were used to test three hypotheses regarding the functional significance of anteroposterior condylar translation − an AoR located inferior to the temporomandibular joint (TMJ) − during chewing: minimizing impingement of the gonial region on cervical soft tissue structures during jaw opening; avoiding stretching of the inferior alveolar neurovascular bundle (IANB); and increasing jaw-elevator muscle torques. The results reveal that the HA is located near the occlusal plane in Papio and Cebus, but closer to the condyle in Macaca; is located anteroinferior to the TMJ during both opening and closing in Papio, as well as during opening in Macaca and Cebus; and varies in its location during closing in Macaca and Cebus. The impingement hypothesis is not supported by interspecific variation in HA location: species with larger gonial angles like Cebus do not have more inferiorly located HAs than species with more obtuse mandibular angles like Papio. However, intraspecific variation provides some support for the impingement hypothesis. The HA seldom passes near or through the lingula, falsifying the hypothesis that its location is determined by the sphenomandibular ligament, and the magnitudes of strain associated with a HA at the TMJ would not be large enough to cause problematic stretching of the IANB. HA location does affect muscle moment arms about the TMJ, with implications for the torque generation capability of the jaw-elevator muscles. In Cebus, a HA farther away from the TMJ is associated with larger jaw-elevator muscle moment arms about the joint than if it were at the TMJ. The effects of HA location on muscle strain and muscle moment arms are largest at large gapes and smallest at low gapes, suggesting that if HA location is of functional significance for primate feeding system performance, it is more likely to be in relation to large gape feeding behaviors than chewing. Its presence in humans is most parsimoniously interpreted as a primitive retention from non-human primate ancestors and explanations for the presence of anteroposterior condylar translation in humans need not invoke either the uniqueness of human speech or upright posture.
Jaw-muscle fiber architecture in tufted capuchins favors generating relatively large muscle forces without compromising jaw gape
2009, Journal of Human Evolution
Citation Excerpt :
Prior to normalization, we measured average sarcomere lengths (Ls) of 2.41 μm for the masseter and 2.43 μm for the temporalis in specimens whose jaws were fixed in occlusion. Earlier studies demonstrate that maximum forces are generated when the jaw is opened beyond incisal occlusion (Nordstrom and Yemm, 1974; Thexton and Hiiemae, 1975; Mackenna and Türker, 1978). Based on this prior work, it seems unlikely that our estimated optimal sarcomere length of 2.41 μm, taken from Rhesus macaque limb muscle (Walker and Schrodt, 1974), is the sarcomere length at which capuchins generate maximum jaw-muscle forces.
Tufted capuchins (sensu lato) are renowned for their dietary flexibility and capacity to exploit hard and tough objects. Cebus apella differs from other capuchins in displaying a suite of craniodental features that have been functionally and adaptively linked to their feeding behavior, particularly the generation and dissipation of relatively large jaw forces. We compared fiber architecture of the masseter and temporalis muscles between C. apella (n = 12) and two “untufted” capuchins (C. capucinus, n = 3; C. albifrons, n = 5). These three species share broadly similar diets, but tufted capuchins occasionally exploit mechanically challenging tissues. We tested the hypothesis that tufted capuchins exhibit architectural properties of their jaw muscles that facilitate relatively large forces including relatively greater physiologic cross-sectional areas (PCSA), more pinnate fibers, and lower ratios of mass to tetanic tension (Mass/P₀). Results show some evidence supporting these predictions, as C. apella has relatively greater superficial masseter and temporalis PCSAs, significantly so only for the temporalis following Bonferroni adjustment. Capuchins did not differ in pinnation angle or Mass/P₀. As an architectural trade-off between maximizing muscle force and muscle excursion/contraction velocity, we also tested the hypothesis that C. apella exhibits relatively shorter muscle fibers. Contrary to our prediction, there are no significant differences in relative fiber lengths between tufted and untufted capuchins. Therefore, we attribute the relatively greater PCSAs in tufted capuchins primarily to their larger muscle masses. These findings suggest that relatively large jaw-muscle PCSAs can be added to the suite of masticatory features that have been functionally linked to the exploitation of a more resistant diet by C. apella. By enlarging jaw-muscle mass to increase PCSA, rather than reducing fiber lengths and increasing pinnation, tufted capuchins appear to have increased jaw-muscle and bite forces without markedly compromising muscle excursion and contraction velocity. One performance advantage of this morphology is that it promotes relatively large bite forces at wide jaw gapes, which may be useful for processing large food items along the posterior dentition. We further hypothesize that this morphological pattern may have the ecological benefit of facilitating the dietary diversity seen in tufted capuchins. Lastly, the observed feeding on large objects, coupled with a jaw-muscle architecture that facilitates this behavior, raises concerns about utilizing C. apella as an extant behavioral model for hominins that might have specialized on small objects in their diets.
Contribution of the digastric muscles to the control of bite force in man
1997, Archives of Oral Biology
The contribution of the (co-contracting) digastric muscles to the rapid decline in bite-force magnitude after unloading of a static bite was investigated by asking participants to perform two different biting tasks with sudden unloading, and correlating the degree of co-contraction of the digastrics (as derived from their electromyograms) with the impact force, the impact velocity (as measured after a travel distance of 5 mm), and the residual force when the jaw system was in static conditions again after the impact. Co-contraction of the digastrics was varied by asking participants to perform the biting task while controlling bite force (force-controlled experiments) or jaw position (position-controlled experiments). In half of the experiments, participants co-contracted their digastrics more strongly in the position-controlled than the force-controlled experiments. However, there was no clear relation between the level of co-contraction and the magnitude of the impact force, the impact velocity and the residual force. The results imply that co-contraction of the digastric muscles is not sufficient to explain the reduction in bite force and the low impact velocity after an unexpected jaw-closing movement. Two other possible mechanisms that reduce forces in an unloaded jaw system are: (1) force-velocity properties of the activated jaw muscles in conjunction with creep of the aponeurotic sheets of the jaw muscles, resulting in a slow partial recovery of the biting force after impact; (2) force-length properties of jaw-opening muscles, an activity not recorded here.
Plasticity of craniomandibular muscle function: <sup>31</sup>P magnetic resonance spectroscopy of the rabbit masseter muscle
1995, American Journal of Orthodontics and Dentofacial Orthopedics
The masseter muscle was studied during postnatal development of the rabbit from the juvenile to adult stage in which the oral function was altered during maturation by modifying the diet to soft food. The muscle was assessed using phosphate magnetic resonance (³¹p NMR) spectroscopy with a single-turn copper surface coil to study potential changes in phosphate metabolism. The ³¹p NMR spectra consisted of five peaks related to unbound forms of inorganic phosphate (Pi), creatine phosphate (PCr), and three peaks related to the adenosine triphosphate (ATP). The masseter was assessed in one group of five rabbits at 8 weeks postnatally (juvenile) and after 4 months of this experimental group masticating on soft food. They were compared with a control group of five rabbits raised on a normal hard diet. The Pi/PCr ratio increased in the adult masseter much higher during twitching, tetany, and periodic contraction than in the juvenile regardless as to whether the adult animal had been raised from the juvenile period on soft or hard diet. There were relatively few differences between the experimental adult animals raised on a soft diet and the normal adult animals despite the soft diet animals demonstrating a significantly lower weight and smaller muscle mass. These findings suggest that chronic underuse of the masseter muscle by decreasing the masticatory loads has a minimal effect on the phosphate metabolism of the maturing masseter. (AM J ORTHOD DENTOFAC ORTHOP 1995;108:168-79.)
Myosin expression in the jaw-closing muscles of the domestic cat and american opossum
1995, Archives of Oral Biology
Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), glycerol SDS-PAGE, two-dimensional electrophoresis, and protein immunoblotting techniques were used to identify myosin heavy chain (MHC) and light chain (MLC) isoforms in limb and masticatory muscles of the cat and American opossum. The fibre types in which these isoforms are expressed were identified by histochemistry and immunohistochemistry. Antibodies specific for the type IIM MHC isoform characteristic of cat jaw-closing muscles and the type I MHC isoform were produced and characterized. The IIM antibody stained the majority of fibres found in the jaw-closing muscles of both species. These IIM-containing fibres characteristically had a histochemical ATPase that remained active after both acid and alkali pre-incubations. A minority of type I fibres was also present in cat jaw-closing muscles, and these reacted positively with antibody specific for type I MHC. It was confirmed that the vast majority of fibres in the cat jaw-closing muscles contained only the characteristic masticatory MHC (IIM) and masticatory MLCs (LClm and LC2m). These muscles did not contain either the type II fibre isoforms of limb muscles or the atrial cardiac (alpha-cardiac) MHC. The type IIM MHC could also be identified in jaw-closing muscles of the opossum. Two-dimensional gel electrophoresis was used to identify the M LC composition of single, histochemically defined, type I fibres in the cat soleus and deep masseter. The type I fibres of limb muscle contained the usual slow MLCs, but type I fibres from the jaw-closing muscles contained only the masticatory light chains.
The force-velocity relation of the rabbit digastric muscle
1987, Archives of Oral Biology
In 30 animals, the digastric was made to pull actively against a slide loaded by a servo-controlled linear motor. Force and velocity were recorded at the end of active shortening to the in-situ (jaw-closed) muscle length. Passive and active force-length relations were also determined in 17 of the rabbits. The empirical force-velocity data were fitted to a hyperbolic equation. The average speed of muscle shortening at zero load was 14.67 cm/s. Mean maximum isometric force at in-situ length (P₀) was 1267 g, and the mean ratio $a P_{0}$ was 0.18. The average time-to-peak twitch tension was 31.8 ms under isometric conditions. In-situ muscle-belly length was about 3 per cent less than optimum length for isometric force. Maximum muscle force was positively correlated with animal size, but maximum velocity showed no relation to force or length. The estimated maximum speed of sarcomere shortening was 26 μm/s, which is slightly slower than in fast limb muscles of the cat, and may indicate the presence of both histochemical type I and II fibres. The isometric force after shortening had ceased was less than P₀, and was correlated with the velocity during shortening. This depression of isometric force may result from an alteration of the excitation-coupling system during activation. These observations suggest a role for the digastric in the rapid acceleration and deceleration of the mandible near the jaw-closed position during opening and closing.

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The twitch-contraction characteristics of opossum jaw musculature

Abstract

Archs oral Biol.

Exp. Neurol.

The active state of mammalian skeletal muscle

J. gen. Physiol.

A new bipolar electrode for electromyography

J. Appl. Physiol.

The correlation of histochemistry and speed of contraction in cat jaw muscles

J. Physiol.

Human locomotion