The skull develops through two different bone-forming pathways, and its growth continues after birth as the brain enlarges. Understanding these processes explains the purpose of infant fontanelles and sutures, the changing proportions of a growing child’s skull, and how premature suture closure can affect skull shape.
During the third week of development, a rod-like structure called the notochord forms along the embryo. Tissue overlying the notochord enlarges and forms the neural tube, which develops into the brain and spinal cord.
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What is a sclerotome?
A medial part of a developing somite that contains mesenchyme, the embryonic tissue that can give rise to connective tissue, cartilage, and bone.
How does intramembranous ossification form skull bones?
Mesenchymal cells gather at a future bone site and differentiate directly into bone-producing cells, without first forming a cartilage model. This process forms the top and sides of the brain case.
What are fontanelles, and why are they useful?
Fontanelles are broad areas of dense connective tissue between developing skull bones. They allow the skull to change shape during birth and provide room for skull expansion as the brain grows after birth.
What is craniosynostosis?
Craniosynostosis is the premature fusion of one or more cranial sutures. It restricts growth along the fused line and can cause compensatory growth and skull deformity.
How does endochondral ossification form skull bones?
Mesenchyme first differentiates into cartilage cells that form a hyaline cartilage model. The model is gradually replaced by bone; this process forms the facial bones and floor of the brain case.
Quiz questions
What embryonic tissue can develop into the connective tissues, cartilage, and bones of the body?Answer: Mesenchyme.
Which skull regions form by intramembranous ossification?Answer: The top and sides of the brain case.
What is the developmental role of fontanelles during birth?Answer: They allow the infant skull to change shape as it passes through the birth canal.
Why can premature closure of the sagittal suture produce a long, narrow head?Answer: Growth across the fused suture is restricted, so skull growth is redirected toward other regions.
Which distinction best describes primary and complex craniosynostosis?Answer: Primary craniosynostosis involves one prematurely fused suture, while complex craniosynostosis involves several.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.