The cranial end of the notochord forms first, and the development of the notochord then proceeds in a caudal direction. This structure is located beneath the neural tube, which gives rise to the brain and spinal cord. The development of the vertebral column begins with the notochord. The mesoderm is also responsible for skeletal muscle, bone, and connective tissue. By the beginning of the third month of development, the cartilaginous structure has begun to ossify into the future vertebral segments. The second stage occurs when these mesenchymal cells differentiate and develop into chondrogenic cells. The first stage consists of embryonic mesenchymal tissue. The notochord evolves into a segmented vertebral structure in three different stages. The notochord, the most primitive form of the axial skeleton, appears during the third week of development. The primary motion of the lower portion of the lower cervical unit is side-bending. The description of all spinal and vertebral movements is relative to motions of their anterior and superior surfaces. The primary motion of the upper portion of the lower cervical unit (C2-C4) is rotation. Vertebrae C3 through C7 are known as "typical" cervical vertebrae. The dens permits pivoting motion and allows a greater range of motion in rotating the head laterally. The dens projects up from the vertebral body and articulates with the atlas. It also functions to bear the weight of the skull, providing support. The primary motions of the OA joint are flexion and extension.Ĭ2, the axis, articulates superiorly with C1 via a unique bony structure called the dens or odontoid process. The OA joint connects the skull to the neck, providing attachment points for some neck muscles. While the cervical spine can undergo flexion, extension, rotation, and side-bending, each individual cervical joint has a primary motion.Ĭ1, the atlas, has no spinous process and articulates with the occipital condyles of the occiput bone of the skull, forming the occipital-atlanto (OA) joint. Cervical vertebrae C1 and C2 are known as "atypical" vertebrae due to the presence of unique bony structures designed to support and move the skull. The cervical spine is composed of seven vertebrae.
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