Week 1 - Embryology of the Skull Flashcards
What bones contribute to the Neurocranium?
- Skull base: Ethmoid, Sphenoid, Occipital base, Petrous Temporal, and Temporal Mastoid
- Cranial vault: Parietal, Frontal, & Squamous Occipital
What is the Neurocranium?
- Cranial vault of the skull (brain case)
- Part that surrounds the developing neural tube
- Comes from paraxial mesoderm and neural crest cells
What is the Viscerocranium?
- Part of the skull that surrounds the developing gut and sense organs
- Face organs
What bones contribute to the Vescerocranium?
- Intramembanous Ossification: Premaxilla, Maxilla, Zygomatic, Temporal, Squamous, Mandible
- Endochondral & Intramembranous Ossification: Malleus, Incus, Stapes, Hyoid, Temporal, Styloid
How does the Neurocranium form?
- Paraxial mesoderm and Somites form skull base via Endochondrial ossification (becomes cartilage first –> bone)
- Neural crest cells form the cranial vault via Intramembranous Ossification (no cartilage precursor)
How do skull bones develop from neural crest mesenchyme?
- Migrates through pharyngeal arch cartilages
- 1st Pharyngeal arch: mandible, malleus, incus
- 2nd Pharyngeal arch: stapes, styloid process
What parts of the adult skull are derived from occipital somites?
Rostral end of the neural tube:
- foramen magnum
- occipital bone
- parts of sphenoid, temporal, and ethmoid bones
What parts of the adult skull are derived from neural crest mesenchyme?
- Frontal bone
- Parietal bone
- Occipital-squamous
- Temporal-squamous
- Zygoma
- Premaxilla & Maxilla
- Malleus, Incus, Stapes
- Hyoid
- Temporal-styloid
- Mandible
What is the importance of sutures in a newborn skull?
Allow shifting of the bones for transit through the narrow birth canal and for growth of the brain.
What is the importance of fontanelles in a newborn skull?
- Separate bones
- Allow shifting
What is molding, and what is the importance of it in a newborn skull?
- Molding: overlapping of flat bones to adapt to narrow pelvic canal (usually returns to position within several days)
- Important for bone shifting
What modifications take place in the skull as we age?
- Maturation from primary ossification centers progresses in a radial fashion toward the periphery of each flat bone.
- Flat bones enlarge by deposition of new layers of bone on the outside and bone resorption on the inside.
- Bone thickening (via osteoclastic activity)
- Synostosis of sutures ages 30-40
- Face maturation: paranasal sinuses develop, tooth eruption, mandible grows, tooth loss induces bone resorption
What is acrania?
-Partial or complete absence of cranial vault
What is anencephaly?
- No brain
- Neural folds fail to elevate and fuse
- Cranial neuropore remains open
What is Meroanencephaly?
- Partial absence of brain
- Remnants of brainstem tissue may be present
What is cranioschisis?
- Cranial vault fails to close due to failure of cranial neuropore to close
- Anterior/rostral NTD
What is craniosynostosis?
- General term for premature closure of sutures
- May not impact neural function
What is Microcephaly?
Small head, usually due to underdeveloped brain.
- Individuals are mentally deficient.
- May be genetic or due to radiation exposure, infectious agents, drugs/alcohol, rubella, or chicken pox during the fetal period.
What is Scaphocephaly?
- Premature closure of sagittal sutures
- Head is long and narrow
What is Oxycephaly?
Premature closure of coronal and lamboidal sutures
-“Tower Skull”
What is Brachycephaly?
Premature closure of bilateral coronal suture
-Wide skull
What is Plagiocephaly?
- Premature closure of one side of coronal OR lambdoidal suture
- Asymmetric face or twisted
What is Trigonocephaly?
Premature closure of frontal suture
