Development of the Vertebral Column | Somites | Axial Skeleton | Embryology

Summary

This video explains the development of the vertebral column, from its formation in the embryo to the stages of ossification and final bone structure. It covers the key structures involved, including the mesoderm, somites, and sclerotomes that form the vertebrae. The script walks through the process of mesenchymal condensation, cartilage formation, and ossification, detailing how vertebrae develop regionally. The video also highlights how the cervical, thoracic, lumbar, sacral, and coccygeal vertebrae form, as well as the unique structures in the Atlas and Axis vertebrae. The video concludes by showing the completed vertebral column's structure.

Takeaways

• 😀 The vertebral column is formed by a series of bones called vertebrae, extending from beneath the cranium to the tip of the coccyx.
• 😀 The vertebral column is divided into five regions: cervical, thoracic, lumbar, sacral, and coccygeal vertebrae, each with distinct features.
• 😀 Each vertebra follows a typical structure, including the vertebral body, vertebral arch, pedicles, laminae, spinous and transverse processes, and articular processes.
• 😀 The intervertebral disc, located between the vertebral bodies, consists of concentric layers of fibrocartilage (annulus fibrosus) and a gelatinous nucleus pulposus.
• 😀 The vertebral foramen forms the space for the spinal cord, with spinal nerves emerging from the spinal cord and passing through intervertebral foramina.
• 😀 Vertebrae develop from mesodermal somites, which are divided into three parts: dermatome, myotome, and sclerotome. The sclerotome forms the vertebrae.
• 😀 The mesenchyme condenses around the notochord, neural tube, and body wall, eventually forming the vertebral column.
• 😀 The process of resegmentation involves the fusion of cranial and caudal portions of somites, leading to the formation of vertebral bodies and intervertebral discs.
• 😀 The vertebral arch forms around the neural tube and later becomes the vertebral arch, while mesenchyme from the body wall contributes to the development of ribs in the thoracic region.
• 😀 Ossification centers begin forming in the vertebral column during the mesenchymal and cartilage stages, and primary ossification centers are established for the centrum and neural arches.
• 😀 Secondary ossification centers appear at puberty and fuse to form the vertebral column's complete structure, including the spinous process, transverse processes, and annular epiphyses.
• 😀 The structure of vertebrae varies across regions, with specific features such as the atlas and axis having unique characteristics, including the fusion of the atlas' centrum with the axis to form the dens.

Q & A

What are the regions of the vertebral column?

The vertebral column is divided into cervical, thoracic, lumbar, sacral, and coccygeal regions.

What is the purpose of the intervertebral disc?

The intervertebral disc, located between the vertebral bodies, provides cushioning and allows for movement between the vertebrae. It consists of the annulus fibrosus (fibrocartilage) and the nucleus pulposus (gelatinous core).

What are the somites and what role do they play in vertebral development?

Somites are segments of the paraxial mesoderm along the dorsal surface of the embryo. Each somite is divided into three parts: the dermatome, the myotome, and the sclerotome. The sclerotome forms the vertebrae.

What is the process of resegmentation in vertebral development?

Resegmentation occurs when the caudal part of one somite fuses with the cranial part of the next somite, resulting in vertebral bodies that span across somite boundaries. This process is essential for forming the vertebral body and intervertebral disc.

What is the role of the notochord in vertebral development?

The notochord serves as a template around which the vertebrae develop. It remains in the intervertebral disc, where it forms the gelatinous nucleus pulposus after resegmentation.

What happens during the mesenchymal stage of vertebral development?

During the mesenchymal stage, mesenchyme condenses around the notochord, neural tube, and body wall, forming the basic structures that will develop into the vertebrae.

How does the vertebral arch form in vertebral development?

The vertebral arch, which surrounds the vertebral foramen and houses the spinal cord, develops from mesenchyme around the neural tube. It eventually ossifies to become part of the vertebra.

What are the primary and secondary ossification centers in the vertebrae?

Primary ossification centers appear first: one for the centrum and one for each neural arch. Secondary ossification centers appear during puberty, including those for the tips of the spinous and transverse processes and the annular epiphyses.

What is the role of the costal elements in vertebral development?

The costal elements, present in all vertebrae, develop into ribs in the thoracic region. They also fuse with the transverse processes in other regions of the vertebral column.

How do the atlas and axis differ from the rest of the vertebrae?

The atlas (C1) has no vertebral body and instead has an anterior arch, while the axis (C2) has a dens formed from the Centrum of the atlas. These two vertebrae are unique in structure compared to the rest of the vertebral column.