At the end of the second week, the blastocyte undergoes a process called gastrulation, which involves formation into a stratified structure composed of the ectoderm, mesoderm, and endoderm. Embryologyĭuring gestation and the first two weeks that follow fertilization, several cellular divisions occur that lead to blastocyst formation. Other features of the axis are the superior articular facets, bifid spinous process, and bilateral transverse foramina. This structure is on the vertebrae's anterior portion and extends superiorly, articulating with the axis above. This vertebra is known as the C2 vertebra and possesses a characteristic feature called the dens or odontoid process. The atlas also contains the transverse ligament between two superior articular facets, an anterior arch and a posterior arch, which acts as a groove for the vertebral artery. The atlas also lacks a spinous process or vertebral body, which distinguishes its structure from the rest of the cervical vertebrae. Below, the atlas articulates with the axis through its bilateral condyles. The atlas is a circular shape that articulates with the cranium above it with the zygapophyseal joints, or lateral masses. The atlantoaxial joint is also surrounded by an articular capsule, which functions to connect the margins of the atlas at the lateral masses with the posterior surface of the axis. In addition to the protection and stabilization of the head, neck, and internal structures, the atlantoaxial joint also facilitates head-neck movements along with the neck muscles. It also allows for blood supply to the brain through the passage of the vertebral artery. This cervical unit also facilitated a protective aspect of the spinal cord from external compression. In general, it stabilizes the head supports the weight in a neutral position. The function of this joint in the cervical spine is multifaceted. Without the atlantoaxial joint, the kinematic capability of the head and neck would not allow for the nearly 600 movements per hour that we make as humans. The multipurpose function of the atlantoaxial joint is crucial in practical application, allowing the head to rotate and turn to the left or right. This joint is unique among the rest of the cervical spine due to its lack of an intervertebral disk. As they reside in the craniovertebral junction at the convergence of the skull and the cervical spine, these two vertebrae are unique among the rest of the cervical spine due to their specific anatomical structure. The uppermost parts of the cervical spine that make up the atlantoaxial joint are the atlas (C1) and the axis (C2). The two bilateral atlantoaxial joints found laterally are classified as gliding joints. These structures are the osteoligamentous rings of the atlas and the transverse ligament, respectively. The median atlantoaxial joint's structure is formed by the dens of C1 vertebrae and two ligamentous structures anteriorly and posteriorly. It consists of three distinct, synovial joints: one medial joint and two lateral atlantoaxial joints. The atlantoaxial joint is a unique joint with multiple distinct structural aspects contributing to its crucial function for cervical stability and mobilization. The pivot joint classification means that it allows for rotation only and is formed by a central pivoting, bony structure that rotates around craniovertebral ligaments. This joint resides in the upper part of the neck between the first and second cervical vertebrae, also known as the atlas and axis, respectively. The atlantoaxial joint is a type of synovial joint that is classified as a biaxial, pivot joint.
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