Morphometric analysis of the human trigeminal nerve.

We evaluated the components of nerve fibers of the motor and sensory roots of the trigeminal nerve by morphometric analysis. Trigeminal nerves were obtained from 5 cadavers (males, aged 67-95) were stained by Masson-Goldner-Goto method and examined under the microscope using a morphometric image-analyzer. The area and perimeter of axons were larger in the motor root than in the sensory root. The size distribution of axons was wider in the motor root than in the sensory root and the distribution pattern was unimodal type. These findings suggested that nerve fibers of the human trigeminal nerve gave similar findings to those of other peripheral nerves, regarding axonal size distribution and relative size of motor and sensory nerve axons.

Morphological differentiation of nerve fibers: central, peripheral, myelinated and unmyelinated.

We have developed a new technique for the morphological differentiation of various nerve fibers which is especially suitable for the morphometric study of nerve fibers of the human nervous system with the help of an image-analyzer. The knowledge from findings by this technique, which is based on several study methods, may be of importance in promoting further neuromorphologic studies and in properly understanding various aspects of neurological symptomatology and the aging process of the nervous system including nerve fibers.

Unmyelinated nerve fibers of the human mandibular nerve.

The aim of this research is to find and to evaluate morphometorically the unmyelinated nerve fibers in the human mandibular nerve using a light microscope. Our report demonstrates for the first time the presence of the unmyelinated nerve fibers of the human mandibular nerve stained by a special method. Our results also indicate that there is a morphometric change with aging in the unmyelinated axons of the nerve.

Development of the human gracilis nucleus: a morphometric evaluation.

The development of the human gracilis nucleus was studied on serial sections of the brain of 9 fetuses and neonates at 18-40 weeks of gestation, a two-month-old infant and a 63-year-old adult using a microscope with a drawing tube and an image-analyzing computer system. A morphometric evaluation revealed that the human gracilis nucleus, whose neurons were distinguished from glia from 18 weeks of gestation onward, showed a gradual development in terms of the columnar volume, neuronal size and number, and revealed two kinds of phenomenon: a normal process which occur in the development of the fetus, viz. natural cell death (also called apoptosis), and a phenomenon due to yet unknown causes regarding a discrepancy between the number of neurons and the neuropil index.

The mandibular nerve in edentulous jaw humans: analysis of myelinated nerve fibers.

We studied the nerve fibers of the human mandibular nerve using edentulous jaw cadavers. We made nitrocellulose sections and stained them with Goto's modification of Masson-Goldner's method in order to evaluate the nerve fibers using an image-analyzer. The results showed an unusual feature: a sudden increase of axonal areas during the decade of the 80s followed by a sharp return to previous levels after that age, even though the number of nerve fibers kept decreasing with the aging process. Although the reason for this is not yet understood, the authors consider that it might be due to compensatory phenomena.

Morphology of the lateral ligament in the human temporomandibular joint.

The morphology of the lateral ligament of the human temporomandibular joint is of two types: ligamentous and without distinct structure. Under the scanning electron microscope, a sheath-like structure that contained bundles of collagen was mainly found in the posterior region of the lateral ligament. Analysis of macromolecular components revealed that type III collagen was mainly present on the collagenous framework of the sheath-like structure. Type I collagen, laminin, and tenascin were found in the framework of the sheath-like structure. Supported collagenous bundles and the distribution of macromolecular components might be related to the stability of the temporomandibular joint. The sheath-like structure and other components of the lateral ligaments store energy and protect the capsule from stress and tension during movements of the jaw.

Development of the motor endplates in the masseter muscle in the human fetus.

The development of the motor endplate (MEP) and the structure of the masseter muscle in the human fetus were examined by light and electron microscopy. At 12 weeks of gestation, the masseter muscle was composed mostly of irregularly-arranged myotubes. The number of muscle fibers increased while that of the myotubes decreases during development. After 28 weeks of gestation, the masseter muscle was composed only of muscle fibers, and these fibers rapidly increased in size in comparison with those prior to 28 weeks of gestation. The MEP appeared during the first 12 weeks of gestation, and were of an undeveloped simple type, with only one axon branch. After 20 weeks of gestation, MEPs were classified as complex or simple types in terms of the branching of the axons. The complex type of MEP was found in muscle fibers of large diameter, while the simple type was found in muscle fibers of small diameter. Schwann-like cells appeared at the surface of the MEP. After 28 weeks of gestation, only the complex type was found in the masseter muscle. These results suggest that, the development of the MEP is closely related to the development of muscle, and that the timing of the development of the masticatory muscles differs from that of other skeletal muscles, such as those in the trunk and limb.

Classification of the ophthalmic artery that arises from the middle meningeal artery in Japanese adults.

In a study of Japanese adults, we found that the orbital branch (OB) passing through the superior orbital fissure frequently anastomosed with the lacrimal artery or the ophthalmic artery (12/20). However, the OB passing through the meningo-orbital foramen (mof) only associationaly anastomosed with branches of the ophthalmic artery (4/79). Furthermore, the OB in the orbit, excluding the lacrimal gland as previously reported. We examined 116 cases in which the OB passed through the mof in 129 adult Japanese cadavers (45.0% in 258 sides). The OB passing through the mof was always distributed to the periorbital region and the area that it supplied was limited to the periorbita in about half of those cases. In another half of the cases (58/116), the area supplied included the lacrimal gland.

Morphology of the nerve terminals of laryngeal muscles in the Japanese monkey (Macaca fuscata).

Laryngeal muscles, namely, the cricothyroid (CT), lateral crico-arytenoid (LCA), thyrio-arytenoid (TA), posterior crio-arytenoid (PCA), interarytenoid (IA) muscles, of Japanese monkeys (body weight, 4.4-8.3 kg; 3-10 years old, male) were examined histologically and by light and scanning electron microscopy. The diameter of muscle fibres with nerve terminals in the CT of the Japanese monkey was larger than that of other laryngeal muscles. However, the areas of nerve terminals varied among laryngeal muscles. The mean diameters of nerve terminals of the CT and PCA were large and basically resembled those of other laryngeal muscles. They contribute mainly to maintenance of phonation which the adductor muscles contribute mainly to postural adjustments of the cartilage. The differences in features of nerve terminals of each muscle suggest the CT and PCA may contribute mainly to the frequency or pitch of voice and intensity of the voice during vocalization and to respiration.

Three-dimensional structure of the perimysium in sternocleidomastoid muscle.

The morphology of the sternocleidomastoid muscle (SCM) of human fetuses, ranged from 12 to 32 weeks gestation, was investigated by a light microscopy and a scanning electron microscopy. The collagenous fibers of the perimysium of the SCM formed complex structures from 24 weeks gestation by contrast to fibers of the endomysium of the SCM. The cross-sectional area (CSA) of the bundle of muscle fibers and the CSA of the individual muscle fibers of the SCM increased during development from 12 to 32 weeks gestation, in a process linked to the development of the perimysium. Therefore the perimysium affects and controls to the muscle fiber of the developed SCM and acts to resisting stretch forces in the movements. The changes in the arrangement and development of the collagenous fibers in the perimysium may be correlated to with these of the muscle fibers.

Morphology and analysis of the development of the human temporomandibular joint and masticatory muscle.

The calcification levels of the mandible and the temporal bone of human fetuses, which ranged from 12 to 32 weeks of gestation, were systematically investigated with a soft X-ray analyzer linked to an image analyzer. The profile of the condylar process (head) revealed high levels of calcification, in contrast to that in the mandibular fossa of the temporal bone. The basal portion of the condylar process and the mandibular notch exhibited moderate calcification from 12 weeks of gestation. The weight and the cross-sectional areas of the muscle and the muscle fibers in masticatory muscles (masseter, temporal, medial, and lateral pterygoid muscles) are all increased gradually during development from 12 to 32 weeks of gestation. These changes in calcification and in cross-sectional area of muscle suggest that muscle development may be related to bone calcification during formation of the mandible.

Morphological analysis of tendinous structure in the American alligator jaw muscles.

In the American alligator, the jaw muscles show seven bundles of tendinous structure: cranial adductor tendon, mandibular adductor tendon, lamina anterior inferior, trap-shaped lamina lateralis, lamina intramandibularis, lamina posterior, and depressor mandibular tendon (originating from the musculus depressor mandibulae, m. pseudotemporalis, m. adductor mandibulae posterior, m. adductor mandibulae externus, m. intramandibularis, m. pterygoideus anterior, and m. pterygoideus posterior). These tendinous structures are composed of many collagen fibrils and elastic fibers; however, the distributions and sizes of the fibers in these tendinous components differ in comparison with those of other masticatory muscles. The differences of these properties reflect the kinetic forces or the stretch applied to each tendon by the muscle during jaw movements in spite of the simple tendon-muscle junctions. © 1993 Wiley-Liss, Inc.

Analysis of the tendinous structure in human masticatory muscles.

In the masticatory muscles, the development of bundles of the tendon was examined: they were composed of many collagen fibers and a few elastic fibers. In the masseter muscle, the property of the tendon differs in the distribution and size of collagen fibers and elastic fibers in comparison with those of other masticatory muscles. This difference is concerned with the kinetic force for the stress or the stretch of each tendon and muscle during jaw movement.