The axial skeleton's embryonic development is a fascinating journey from simple cells to complex structures. It involves two main processes: for flat skull bones and for the and vertebral column.
The formation of the vertebral column, , and is a intricate dance of cellular differentiation and migration. , the soft spots on a baby's head, play a crucial role in birth and early brain growth, gradually closing as the skull develops.
Embryonic Development of the Axial Skeleton
Types of skull bone development
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Top images from around the web for Types of skull bone development
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differentiate directly into , which are the cells responsible for bone formation
Osteoblasts secrete osteoid matrix, a protein-rich substance that calcifies to form bone tissue (frontal and parietal bones)
Occurs in the flat bones of the skull, such as the frontal, parietal, and parts of the occipital and temporal bones, resulting in the formation of the
Mesenchymal cells differentiate into , which are cells that produce cartilage, forming a cartilage model of the future bone ()
hypertrophy (enlarge) and die, leaving cavities in the cartilage matrix
Blood vessels and osteoblasts invade the cavities, depositing bone matrix and replacing the cartilage with bone tissue
Occurs in the base of the skull, including the ethmoid, sphenoid, and parts of the occipital and temporal bones, forming the skull base
Formation of axial skeleton
Vertebral column
, which are blocks of , differentiate into , which are the embryonic precursors of the
Sclerotomes migrate and surround the , a flexible rod-like structure that provides support to the embryo
Sclerotomes undergo endochondral ossification to form the vertebral bodies and arches, creating the segmented structure of the spine
degenerates, leaving the , the gelatinous center of the , which provide cushioning between the vertebrae
Ribs
, which are embryonic rib precursors, develop from the thoracic (chest) sclerotomes
Costal processes elongate and undergo endochondral ossification to form the ribs, which protect the thoracic organs (heart and lungs)
, which are two parallel cartilaginous structures, develop from the ventrolateral (front and side) body wall mesenchyme
Sternal bars fuse in the midline to form the cartilaginous sternum, the breastbone
Sternum undergoes endochondral ossification, with multiple , to form the bony sternum, which serves as an attachment point for the ribs
Fontanelles in infant skulls
are fibrous membrane-covered gaps between the incompletely ossified bones of the infant skull, allowing for flexibility and growth
Allow for skull deformation during birth, facilitating passage through the birth canal, which is essential for successful delivery
Provide space for rapid brain growth during the first year of life, accommodating the increasing size of the brain
Located at the junction of the frontal and parietal bones, at the top front of the skull
Normally closes between 12-18 months of age, indicating proper skull development
Located at the junction of the parietal and occipital bones, at the back of the skull
Normally closes between 2-3 months of age, earlier than the anterior
Sphenoidal and mastoid fontanelles
Located at the junctions of the temporal, parietal, and sphenoid/occipital bones, on the sides of the skull
Close within the first few months of life, contributing to the stability of the skull
Delayed closure or abnormal enlargement of fontanelles may indicate underlying developmental disorders () or increased intracranial pressure (), requiring medical attention
As fontanelles close, form, allowing for continued skull growth and flexibility
Developmental processes in axial skeleton formation
: The process by which cartilage models of future bones are formed
contribute to the formation of the skull, particularly the facial bones and parts of the skull vault
Ossification centers appear within the cartilage models, initiating the process of bone formation and growth