Biomedical subjects

J A Korfage

Publications and source records attributed to J A Korfage.

9 recordsLinked to original sources

PubMed2001

Differences in myosin heavy-chain composition between human jaw-closing muscles and supra- and infrahyoid muscles.

Jaw-closing muscles have architectural features suited to force production; supra- and infrahyoid muscles are better adapted to produce velocity and displacement. It was hypothesized that this difference in function would be reflected in myosin heavy-chain (MyHC) composition (equivalent to contraction velocity) and fibre-type cross-sectional area (equivalent to force). MyHC composition was determined in muscles obtained from eight human cadavers, using monoclonal antibodies against MyHC isoforms. Jaw closers contained 4.2 times fewer type IIA fibres and 5.2 times more hybrid fibres than suprahyoid muscles, and 3.9 times fewer type IIA fibres and 3.2 times more hybrid fibres than the infrahyoid muscles. In the jaw closers, MyHC-I was expressed in approx. 70% of all fibres (pure+hybrid), in the suprahyoid muscles in approx. 40%, and in the infrahyoid muscles in approx. 46%. In the jaw closers, type I fibres were 40% larger in diameter than in the supra- and infrahyoid muscles. It can be concluded that the jaw closers have characteristics of slow muscles, and that the supra-/infrahyoid muscles have characteristics of fast muscles.

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PubMed2000

Intermuscular and intramuscular differences in myosin heavy chain composition of the human masticatory muscles.

Among and within the human masticatory muscles a large number of anatomical differences exists indicating that different muscles and muscle portions are specialized for certain functions. In the present study we investigated whether such a specialization is also reflected by intermuscular and intramuscular differences in fibre type composition and fibre cross-sectional area. Fibre type compositions and fibre cross-sectional areas of masticatory muscles were determined in eight cadavers using monoclonal antibodies against myosin heavy chain (MyHC). The temporalis, masseter and pterygoid muscles could be characterized by a relatively large number of fibres containing more than one MyHC isoform (hybrid fibres). In these muscles a large number of fibres expressed MyHC-I, MyHC-fetal and MyHC-cardiac alpha. Furthermore, in these muscles type I fibres had larger cross-sectional areas than type II fibres. In contrast, the mylohyoid, geniohyoid and digastric muscle were characterized by less hybrid fibres, and by less fibres expressing MyHC-I, MyHC-fetal, and MyHC-cardiac alpha, and by more fibres expressing MyHC-IIA; the cross-sectional areas of type I and type II fibres in these muscles did not differ significantly. Compared to the masseter and pterygoid muscles, the temporalis had significantly larger fibres and a notably different fibre type composition. The mylohyoid, geniohyoid, and digastric muscles did not differ significantly in their MyHC composition and fibre cross-sectional areas. Also intramuscular differences in fibre type composition were present, i.e., a regionally higher proportion of MyHC type I fibres was found in the anterior temporalis, the deep masseter, and the anterior medial pterygoid muscle portions; furthermore, significant differences were found between the bellies of the digastric.

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PubMed2000

Myosin isoform composition of the human medial and lateral pterygoid muscles.

The medial and lateral pterygoid muscles are different in structure as well as in function. The medial pterygoid muscle is concentrically active during jaw closing, and the superior head of the lateral pterygoid muscle is eccentrically active during jaw closing, while its inferior head is concentrically active during jaw opening. Architecturally, the medial pterygoid can deliver higher forces than the lateral pterygoid. We investigated whether these differences are reflected in the myosin heavy-chain (MyHC) composition and the fiber cross-sectional area (f-csa) of these muscles. The pterygoid muscles from eight cadavers were investigated by means of monoclonal antibodies against different isoforms of MyHC. The proportions of pure MyHC type I fibers did not differ significantly among the muscles (32% in medial pterygoid, 34% in superior head, and 36% in the inferior head of the lateral pterygoid), nor did the total proportions of pure MyHC type IIA and IIX fibers (16% in medial pterygoid, 26% in the superior head, and 19% in the inferior head of the lateral pterygoid). The mean f-csa of type I fibers was 1315 microm2, which did not differ significantly among the muscles, and was significantly larger than the f-csa of type IIA fibers. The relative proportions of hybrid fibers, which expressed more than one MyHC isoform, were 52% in the medial pterygoid, 40% in the superior head, and 45% in the inferior head of the lateral pterygoid and did not differ significantly among the muscles. The most abundant hybrid fiber types found were fibers expressing MyHCs-cardiac alpha+IIA and MyHCs-cardiac alpha+I+IIA. Significant regional differences were found in the proportions of MyHC type I fibers in the medial pterygoid and in the inferior head of the lateral pterygoid. Although the form and function of the muscles are different, we conclude that this is not reflected in their myosin isoform composition.

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PubMed1999

Regional differences in fibre type composition in the human temporalis muscle.

Anatomical and electromyographic studies point to regional differences in function in the human temporalis muscle. During chewing and biting the anterior portions of the muscle are in general more intensively activated and they are capable of producing larger forces than the posterior portions. It was hypothetised that this heterogeneity in function is reflected in the fibre type composition of the muscle. The composition and surface area of different fibre types in various anteroposterior portions of the temporalis muscle were investigated in 7 cadavers employing immunohistochemistry with a panel of monoclonal antibodies against different isoforms of myosin heavy chain. Pure slow muscle fibres, type I, differed strongly in number across the muscle. In the most posterior portion of the muscle there were 24% type I fibres, in the intermediate portion 57%, and in the most anterior portion 46%. The mean fibre cross-sectional area (m-fcsa) of type I fibres was 1849 microm2, which did not differ significantly across the muscle. The proportion of pure fast muscle fibres, type IIA and IIX, remained more or less constant throughout the muscle at 13% and 11% respectively; their m-fcsa was 1309 microm2 and 1206 microm2, respectively, which did not differ significantly throughout the muscle. Pure type IIB fibres were not found. The relative proportion of hybrid fibres was 31% and did not differ significantly among the muscle portions. Fibre types I + IIA and cardiac alpha + I + IIA were the most abundant hybrid fibre types. In addition, 5% of the type I fibres had an additional myosin isoform which has only recently been described by means of electrophoresis and was named Ia. In the present study they were denoted as hybrid type I + Ia muscle fibres. It is concluded that intramuscular differences in type I fibre distribution are in accordance with regional differences in muscle function.

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PubMed1997

Architecture of the human jaw-closing and jaw-opening muscles.

BACKGROUND: The human jaw-closing and jaw-opening muscles produce forces leading to the development of three-dimensional bite and chewing forces and to three-dimensional movements of the jaw. The length of the sarcomeres is a major determinant for both force and velocity, and the maximal work, force, and shortening range each muscle is capable of producing are proportional to the architectural parameter volume, physiological cross-sectional area, and fiber length, respectively. In addition, the mechanical role the muscles play is strongly related to their three-dimensional position and orientation in the muscle-bone-joint system. The objective of this study was to compare relevant architectural characteristics for the jaw-closing and jaw-opening muscles and to provide a set of data that can be used in biomechanical modeling of the masticatory system. METHODS: In eight cadavers, sarcomere lengths, muscle masses, fiber lengths, pennation angles, and physiological cross-sectional areas were determined for the following muscles: superficial and deep masseter, anterior and posterior temporalis, anterior and posterior medial pterygoid, inferior and superior lateral pterygoid, posterior and anterior digastric, geniohyoid, posterior and anterior mylohyoid, and stylohyoid. To determine the spatial position of their action lines, the three-dimensional coordinates of the attachment sites were registered. RESULTS: Compared with the jaw openers, the jaw closers were characterized by shorter sarcomere lengths at the closed jaw, larger masses of contractile and tendinous tissue, larger physiological cross-sectional areas, larger pennation angles, shorter fiber lengths, shorter moment arms, and lower fiber-length-to-muscle-length ratios. In addition, architectural features differed across the muscles of the same functional group. Sarcomere length did not differ significantly among the regions of the same muscle. In contrast, in some muscles, significant intramuscular differences were found with respect to, e.g., physiological cross-sectional area, fiber length, pennation angle, and moment arm length. CONCLUSIONS: The results suggest that the jaw-closing muscles have architectural features that suit them for force production. Conversely, the jaw-opening muscles are better designed to produce velocity and displacement.

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PubMed1995

Function-dependent anatomical parameters of rabbit masseter motor units.

Rabbit masseter motor units (22) were studied by stimulation of trigeminal motoneurons. We tested the hypotheses that masseter motor units facilitate fine motor control by concentrating fibers in small areas and that the distribution of motor unit fibers depends on the fiber type. The twitch contraction time and the isometric tetanic force were registered. The motor unit fibers were depleted of their glycogen by prolonged stimulation. Serial sections of the entire muscle were stained with the periodic acid Schiff (PAS) and monoclonal antibody stains. The muscle fibers of the motor unit were mapped and identified by four myosin heavy-chain (MHC) isoforms: I, IIA, IID, and cardiac-alpha. In the PAS-stained sections, anatomical parameters of the motor units, affecting the force output, were analyzed: the innervation ratio (IR), motor unit territory area (TA), and relative (R-DENS) and absolute (A-DENS) motor unit fiber densities. The fiber cross-sectional area (F-CSA) was measured for each MHC fiber type. The F-CSA sum of all motor unit fibers, the physiological cross-sectional area (P-CSA), was calculated. The IR ranged between 77 and 720 fibers (mean, 267). The mean TA was 8.71 mm2 (range, 4.45 to 19.58). The mean R-DENS was 10 fibers per 100; the A-DENS was 31 fibers per mm2. Linear correlations were found between the IR and the R-DENS and between the tetanic force and the IR. The F-CSAs showed a stepwise increase in value from type I- to IID-MHC fibers. The mean P-CSA was 0.90 mm2 (range, 0.09 to 2.97). A high linear correlation was noted between the P-CSA and the tetanic force. In conclusion, increase of motor unit size expressed in higher fiber counts and forces is accomplished by increase of the fiber density. Thus, forces can be exerted selectively in restricted regions of the masseter muscle. Differences in fiber orientation due to complex muscle pinnation emphasize the possibility of an accurate muscle performance.

Analysis of Variance↗

PubMed1993

Motor unit territories and fiber types in rabbit masseter muscle.

The myosin heavy chain (MHC) content and spatial distribution of the fibers of 11 motor units (MUs) of the rabbit masseter muscle were determined. The fibers of single MUs were visualized in whole-muscle serial sections by a negative periodic acid/Schiff reaction for glycogen after they had been depleted of glycogen by extracellular stimulation of their motoneuron in the trigeminal motor nucleus. The MHC isoforms present in the fibers were characterized by monoclonal antibodies. Individual fibers appeared to contain from one to three MHC isoforms. In six cases, all fibers of a motor unit had an identical MHC content; in five cases, different fiber types were found in a single unit. The fiber number per MU varied between 40 and 424, the territory size between 1.1 and 11.0 mm2 (of a total muscle cross-section of 200 mm2), and fiber density between 6 and 17 MU fibers per 100 muscle fibers. In the multipennate masseter, the fibers were usually restricted to a single anatomical compartment. In comparison with leg muscles, the fibers of the masseter motor units, although similar in number, were restricted to relatively smaller subvolumes of the muscle and thus reached higher densities in their territories. The small territories are the anatomical substrate for the observed heterogeneity of motor behavior. Since the different anatomical compartments of the masseter differ with respect to their biomechanical capabilities, this makes this muscle multifunctional in the exertion of complex motor tasks.

Animals↗

PubMed1991

Demonstration of 'cardiac-specific' myosin heavy chain in masticatory muscles of human and rabbit.

Human and rabbit masticatory muscles were analyzed immuno- and enzyme-histochemically using antibodies specific to 'cardiac' alpha, slow and fast myosin heavy chain isoforms. In human masseter, temporalis, and lateral pterygoid muscle 'cardiac' alpha myosin heavy chain is found in fibres that contain either fast, or fast and slow myosin heavy chain. In rabbit masseter, temporalis and digastric muscles, fibres are present that express 'cardiac' alpha myosin heavy chain either exclusively, or concomitantly with slow myosin heavy chain or fast myosin heavy chain. Our results demonstrate a much broader distribution of 'cardiac' alpha myosin heavy chain than hitherto recognized and these might explain in part the specific characteristics of masticatory muscles. The 'cardiac' alpha myosin heavy chain is only found in skeletal muscles originating from the cranial part of the embryo (including the heart muscle), suggesting that its expression might be determined by the developmental history of these muscles.

Adult↗

PubMed1989

The functional significance of the position of the centre of rotation for jaw opening and closing in the rabbit.

In the rabbit, jaw opening and closing occurs in combination with condylar protrusion and retraction. Consequently the centre of rotation (CR) for the movement lies in the inferior portion of the ascending ramus of the mandible, far below the condyle. This location is stable and independent of the type of food being chewed and the age of the animal. The topography of the soft tissues at the posterior border of the ramus is adapted to the movement pattern. The facial nerve crosses the space between skull and mandible at the level of the CR. The parotid gland lies behind the ramus between condyle and CR; below the CR, the gland is replaced by loose adipose tissue. A computer model was used to demonstrate that the location of the CR determines the amount of stretch of the large masseter and medial pterygoid muscles. Using parameters for passive elastic behaviour of muscle, obtained by postmortem measurements, it can be shown that the normal CR position minimises muscle stretch and passive elastic forces. Even a small upward displacement of the CR causes a significant amount of resistance in the jaw-closers at gapes comparable to those reached in natural mastication. A second, less dramatic effect of increased muscle stretch is a sharper decline of maximum possible active closing force, due to the interrelationship of fibre length and isometric tension. In young animals, the muscle fibres are relatively long but stiff; in adults they are shorter, but more compliant. In both ages the CR is located in such a way that masseter and medial pterygoid stretching is minimised. The high position of the temporomandibular joint ensures a maximal leverage for the muscles mentioned above. By separating the point where the reaction forces apply (the joint) from the location of the rotational axis, maximum leverage and minimal length changes of the jaw-closing muscles are achieved simultaneously. It is further suggested that elastic muscular forces play a role in determining the position of the CR.

Animals↗