Innervation and functional characteristics of connective tissues, especially elastic fibers, in human fetal thoracic intervertebral articular capsule and its surroundings

Abstract

The articular capsules between the thoracic vertebrae, which have physiologically different functions from those of other levels of the vertebrae, have yet to be subjected to neuro-anatomical and fine structural analysis. In the present study, we analyzed serial frozen sections of decalcified thoracic vertebrae in human fetuses, and identified the articular capsule tissue with its unique distribution of elastic fibers. The fine structure of the elastic fibers was studied by transmission electron microscopy. In the early-stage fetus, the fibrous membrane forming the lateral intervertebral articular capsule contained abundant thin elastic fibers consisting of microfibrils. In the late-stage fetus, the lateral capsule of fibrous membrane was occupied by thick elastic fibers. A medial articular capsule, namely the ligamenta flava, contained numerous thick elastic fibers in both early and late-stage fetuses. The distributional differences in nerve fibers between early and late-stage fetuses were determined by immunostaining, using antibodies raised against protein gene product 9.5 (PGP 9.5; ubiquitin carboxyl-terminal hydrolase). Innervation by PGP 9.5 immunoreactive fibers was limited to the areas of the articular capsules near the blood vessels, which may indicate their functional relation with blood flow. No PGP 9.5 immunoreactive fibers were found in the ligamenta flava of the late-stage fetus. Innervation might be directly involved in the development of the intervertebral articular capsules in normal human fetuses.

Distribution of elastic fibers in the head and neck: a histological study using late-stage human fetuses

“…We are aware of limited examples of smooth muscle that are not closely related to vessels in the fetal head: the orbitalis muscle behind the orbit [4] and the ciliary muscle. However, elastic fibers can be present without associated smooth muscle in specific structures such as elastic cartilages, the nuchal ligament [5], the yellow ligament (ligamentum flavum) [6, 7], the skin dermis [8], and the facet capsule of the vertebral column [9]. In the last case, Shiraishi et al [9] used human fetal material for their research.…”

“…However, elastic fibers can be present without associated smooth muscle in specific structures such as elastic cartilages, the nuchal ligament [5], the yellow ligament (ligamentum flavum) [6, 7], the skin dermis [8], and the facet capsule of the vertebral column [9]. In the last case, Shiraishi et al [9] used human fetal material for their research. Likewise, specific fascial structures in the human pelvic floor contain elastic fibers without any association with smooth muscle [10-13].…”

Elastic fiber‐mediated enthesis in the human middle ear

“…did not confirm the presence of elastin or elastic fibers at the joint, especially at the enthesis. In fact, some joint capsules in the human body are known to contain elastic fibers, for example at the facet joint of the vertebral column (Shiraishi et al. 2003) and at the temporomandibular joint (Caltabiano et al.…”