University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

127

Pages:

2
Author:

Mariam A.

SKULL EMBRYOLOGY  Cranium divided into neurocranium and viscerocranium. o Neurocranium forms a protective case around the brain. o Viscerocranium forms the skeleton of the face. Viscerocra nium Neurocrani um  Neurocranium. o Separated into two portions; membranous and cartilaginous. o Membranous portion consists of flat bones which surround the brain as a vault. It is derived from neural crest (NC) cells and paraxial (PA) mesoderm. When stimulated by TGF-β, these two sources undergo intramembranous ossification of the calvaria (foetal skull). Primary ossification centres form in bone spicules that radiate outwards but remain separate by sutures. o Cartilaginous (base of skull) initially consists of a number of separate cartilages. Those in front of the cranial notochord (sella tucica) are NC derived, making up the prechordal chondrocranium. Those that are behind are derived from occipital PA, making up the chordal chondrocytes. Base of the skull is formed when these cartilages fuse and ossify by endochondral ossification.  Viscerocranium. o Facial skeletons that are formed from the first two pharyngeal arches. o The first arch gives rise to a dorsal portion, the maxillary process, which extends forward and gives rise to the maxilla, zygomatic bone, part of the temporal bone and nasal and lacrimal bones. o The ventral portion of the first arch, the mandibular process, contains the Meckel cartilage which condenses and ossifies by intramembranous ossification to give rise to the mandible. o The dorsal tip of the mandibular process, along with that of the second pharyngeal arch, later gives rise to the incus, malleus and stapes, along with the styloid process and hyoid bone.