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Objective: The myodural bridge (MDB) connects the suboccipital musculature to the spinal dura mater (SDM) as it passes through the posterior atlanto-occipital and the atlanto-axial interspaces. It has recently been proposed that head movement may assist in powering the movement of cerebrospinal fluid (CSF) via muscular tension transmitted to the SDM via the MDB. Methods: The present study utilized dogs as the experimental model to explore the MDB's effects on the CSF pressure (CSFP) during stimulated contractions of the suboccipital muscles as well as during manipulated movements of the atlanto-occipital and atlanto-axial joints. Additionally biomechanical tensile strength tests were conducted. Results: The tensile strength of the collagenous fibers passing through the dorsal atlanto-occipital and atlanto-axial interspaces were 0.16±0.04 MPa and 0.82±0.57 MPa, respectively. Passive head movement, including lateral flexion, rotation, as well as flexion--extension, all significantly increased CSFP. Furthermore, the CSFP was significantly raised from 12.41± 4.58 to 13.45±5.16 mm Hg when the obliquus capitis inferior (OCI) muscles of the examined specimens were electrically stimulated. Head movements appeared to be an important factor affecting CSF pressure, with the MDB of the suboccipital muscles playing a key role in this process. Conclusion: The present study provides direct evidence to support the hypothesis that the MDB may be a previously unappreciated significant power source (pump) for CSF circulation. [ABSTRACT FROM AUTHOR]

Objective: Myodural bridge complex (MDBC) is a new functional complex structure including the rectus capitis dorsal minor (RCDmi), rectus capitis posterior major (RCPma), obliquus capitis inferior (OCI), nuchal ligament (NL), vertebrodural ligament (VDL) and dense MDB fibers originate from these muscles and ligaments. We firstly proposed that the MDBC could be a significant contributor to CSF (Cerebrospinal Fluid) dynamics at the craniocervical junction in addition to other factors such as heartbeat and respiration. MDBC was found to exist in the vast majority of studied amphibians, birds, reptiles and mammals in our study. It was considered as an evolutionarily conserved structure. During the landing process of the vertebrates, the morphological evolution process of MDBC and its regulatory mechanism that adapt to the terrestrial living environment remains unclear. Methods: Anatomical, multiple histologic staining methods and scanning electron microscopy observation were used in the present study to compare and analyze the morphological differences among the MDBC in different animals. Results: It was found that MDBC/MDBC-like structures widely existed in vertebrates. It was also found that MDBC/MDBC-like structures exist throughout the vertebral tubes in fish, but for amphibians, birds, reptiles and mammals, the MDBC is concentrated in the cervical vertebral segments. Conclusion: Our study implies that the transformation of amphibian MDBC/MDBC-like structures might be an adaptive change in the evolution of the vertebrate from water to land. [ABSTRACT FROM AUTHOR]