What are the two main parts of the skull and how do they develop?

The skull is divided into the neurocranium (encloses the brain) and the viscerocranium (forms the facial skeleton). Both develop from mesenchyme surrounding the developing brain, with the neurocranium further splitting into cartilaginous and membranous components.

How does the neurocranium form, and what are its key components?

The neurocranium forms via two processes: Cartilaginous neurocranium develops by endochondral ossification from structures like trabeculae cranii and parachordal cartilage, contributing to bones such as the ethmoid and occipital. Membranous neurocranium forms flat bones like the frontal and parietal through membranous ossification.

What is the viscerocranium, and which structures contribute to its development?

The viscerocranium is the facial skeleton, derived primarily from the first and second pharyngeal arches. Key contributions include the maxillary process forming the maxilla and zygomatic bones, the mandibular process containing Meckel’s cartilage for the mandible, and ear ossicles developing from dorsal arch parts.

What are the different types of skull ossification, and can you give examples?

Skull ossification occurs in three types: Membranous bones form directly from mesenchyme, e.g., frontal and parietal bones. Cartilaginous bones develop via endochondral ossification, e.g., ethmoid bone. Membranocartilaginous bones have both types, e.g., sphenoid and mandible.

What are fontanelles, and why are they important in newborns?

Fontanelles are soft spots in a newborn’s skull where sutures haven’t closed. They allow for moulding during birth and postnatal skull expansion and brain growth. Clinically, they help assess hydration (sunken) or intracranial pressure (bulging).

What are some common skull shape abnormalities and their causes?

Skull shape abnormalities often result from premature suture closure, including scaphocephaly (long, narrow skull from early sagittal closure), brachycephaly (short skull from bilateral coronal closure), plagiocephaly (asymmetry from unilateral closure), and microcephaly (small skull from poor brain development).

How does the newborn skull differ from an adult skull?

The newborn skull has a large neurocranium relative to the viscerocranium and features fontanelles (soft spots). This disproportion is due to early brain growth and underdeveloped facial bones and sinuses.

Skull Development – Neurocranium & Viscerocranium

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