Cranial Embryology Flashcards
Cartilaginous bones are formed by:
endochondrial ossification
membranous bones are formed by:
intramembranous ossification
What are examples of membranous bones in the neuro- and viscero- cranium?
Neurocranium: vault bones
Viscerocranium: facial bones
What are examples of cartilaginous bones in the neuro- and viscero- cranium?
neurocranium: cranial base bones
viscerocranium: ossicles, hyoid bone
Skull bones and cartilage are derived from what three types of tissues?
outer epithelium (mostly), local mesoderm and migrating neural crest cells
What helps form the eventual shape of the skull?
soft tissues (brain, CT, muscle)
Prior to fusion, what structures span the membranous vault bones of the neurocranium?
fontanelles
What type of joint joins the frontal, ethmoid, sphenoid and occipital bones?
synchondrosis
When do the spheno-ethmoidal and spheno-occipital joints close?
mid-late teens
How do the temporal and sphenoid bones grow?
laterally
How is the position of the mandible determined?
the sphenoid grows along the cephalic angle, forming the cranial base
overbites and square jaws are associated with what type of cephalic angles/cranial base angles?
large angles
wide-angled mandibles and mandibular protrusion are associated with what type of cephalic angle/cranial base angle?
small angles
What are the pharyngeal arches? What are they normally associated with?
condensations of mesenchyme and neural crest cells, give rise to structures of the face and neck. associated with: cranial nerves, cartilage and arteries
Once the cartilages of pharyngeal arches regress, they are replaced normally via what process?
intramembranous ossification (for the facial bones)
What two bony structures are NOT formed by membranous ossification in the viscero and neuro cranium?
the styloid process and the hyoid
Pharyngeal groove 1 develops into:
the external auditory meatus
Pharyngeal pouch 1 develops into:
tympanic cavity/auditory tube
Pharyngeal pouch 2 develps into:
the palatine tonsil
pharyngeal pouch 3 develops into:
thymus, parathyroid gland, which migrate down the neck
pharyngeal pouch 4 develops into:
the parathyroid and C cells of the thyroid, which migrate down the neck
The thyroid gland, as it develops, descends through what:
the foramen cecum, thyroglossal duct, to be anterior to the hyoid bone and larynx
What is a pyramidal lobe?
a piece of thyroid tissue that did not migrate exactly to the target area but is still connected to the rest of the thyroid tissue
What are three abnormalities which can occur from thyroid malmigration?
ectopic thyroid tissue, cysts (fistulas as well) and pyramidal lobes
The face and facial structures form from what pharyngeal arch?
the 1st pharyngeal arch
What occurs during facial development?
medial migration and fusion of nasal and maxillary structures, early fusion of the mandibular processes
What is the cause of a cleft lip?
failure of the maxillary and medial nasal prominences to fuse properly
What is the cause of a cleft palate?
failure in the fusion of the palatine proceses
How is the palate formed?
fusion of the palatine processes of the maxilla with the septum, separate the oral and nasal cavities
What are three facial characteristics of fetal alcohol syndrome? what are they caused by?
- smooth philtrum
- thin upper lip
- eyes wide apart
due to incorrect closure of the maxillary and nasal prominences
