Skull Joints: Fontanelles, Sutures, TMJ & Synchondroses | Anatomy

Summary

This video explores the development of the human skull from infancy to adulthood. It explains the concept of fontanelles, the flexible gaps in a newborn's skull that allow for brain growth and ease during birth. As the child grows, these fontanelles close and are replaced by sutures, which are immovable joints in the adult skull. The video also covers different types of skull joints, including immovable sutures, synchondroses, gomphoses, and the unique temporomandibular joint (TMJ), which is the only movable joint in the skull. Clinical notes are also provided to highlight the significance of these anatomical changes.

Takeaways

• 😀 Newborns have gaps in their skull, called fontanelles, which provide flexibility during birth and space for brain growth in early development.
• 😀 As a child grows, the fontanelles gradually close, and the skull's bones fuse to form immovable joints called sutures, except for the movable temporomandibular joint (TMJ).
• 😀 The viscerocranium (facial part of the skull) is much smaller in newborns compared to the neurocranium, and grows as the child develops, especially with the eruption of teeth.
• 😀 Newborns have higher nasal resistance due to smaller nasal cavities, making them more prone to airway obstruction and difficulty clearing nasal congestion.
• 😀 The paranasal sinuses are underdeveloped or rudimentary in newborns, which contributes to their smaller facial structure.
• 😀 The size of the head is disproportionately larger in newborns, making up about one-fourth of the body length, compared to one-seventh in adults.
• 😀 Fontanelles are soft, membranous gaps between skull bones, and their closure patterns are important for clinical assessments of a baby’s health.
• 😀 The skull's sutures, which connect the bones in an adult, are immovable joints (synarthroses), and they were once flexible gaps in infants.
• 😀 The temporomandibular joint (TMJ) is the only movable joint in the skull, allowing jaw movement for functions like chewing and speaking.
• 😀 The adult skull also has synchondroses (immovable cartilage joints) and gomphoses (fibrous joints), like the connection between teeth and the jawbone.

Q & A

What is the purpose of the gaps in a newborn’s skull?

The gaps in a newborn’s skull, called fontanelles, allow the skull to remain flexible during birth and provide space for the brain to grow rapidly in the early stages of life.

At what age do the fontanelles typically close?

Most fontanelles begin to close between the first few months and around 18 to 24 months of age. The timing can vary slightly between individuals.

What are the main differences between a newborn skull and an adult skull?

The three main differences are: 1) A newborn’s facial bones (viscerocranium) are much smaller relative to the neurocranium. 2) A newborn’s head makes up about one-fourth of its body length, while an adult’s head is about one-seventh. 3) Newborn skulls have open sutures and fontanelles, while adult skulls have ossified sutures and closed fontanelles.

Why are newborns more prone to airway obstruction and nasal congestion?

Newborns have a narrow inferior meatus in their nasal cavity, leading to higher nasal resistance (about 3.5 times higher than adults), which makes them more susceptible to airway obstruction and difficulty clearing nasal congestion.

What are fontanelles and why are they clinically significant?

Fontanelles are flexible gaps between the bones of a newborn's skull, covered by connective tissue. Clinically, they are important because changes in their shape or closure can indicate medical conditions such as dehydration, increased intracranial pressure, or craniosynostosis.

What are the four main fontanelles in a newborn’s skull?

The four main fontanelles are: 1) Anterior fontanelle (diamond-shaped), 2) Posterior fontanelle (triangular), 3) Sphenoid fontanelle (anterolateral), and 4) Mastoid fontanelle (posterolateral). Each has a typical closure timeline.

What is craniosynostosis, and how does it relate to fontanelles?

Craniosynostosis is a condition where one or more sutures of the skull close prematurely, restricting brain growth. If fontanelles close too early, especially involving the sutures, it can lead to craniosynostosis, requiring potential surgical intervention.

How do sutures differ from fontanelles in the skull?

Sutures are fibrous joints that connect bones in the adult skull, while fontanelles are flexible gaps filled with connective tissue in a newborn’s skull. Over time, fontanelles close and become sutures, which eventually ossify into rigid bone connections.

What is the only movable joint in the adult skull?

The temporomandibular joint (TMJ) is the only freely movable joint in the adult skull, allowing for jaw movement during activities like chewing and speaking.

What is the difference between a synchondrosis and a gomphosis joint in the skull?

A synchondrosis is an immovable joint where bones are connected by hyaline cartilage, typically found at the base of the skull during development. A gomphosis is a joint found only between teeth and jawbones, where a tooth is held in place by a periodontal ligament, allowing minimal movement for shock absorption during chewing.