Embryology of Head

Question 1

What bones form the neurocranium? How are they formed?

Answer 1

Frontal, parietal, squamous portion of temporal, interparietal portion of occipital

Intramembranous ossification

Question 2

What bones form the viscerocranium? How are they formed?

Answer 2

Facial bones: intramembranous ossification

Ossicles, hyoid: endochondral ossification

Question 3

What bones form the cranial base? How are they formed?

Answer 3

Ethmoid, sphenoid, petrous portion of temporal, occipital

Endochondral ossification

Question 4

What is the spheno-occipital synchondrosis and when does it close?

Answer 4

A fibrous joint between the sella turcica part of the sphenoid and the occipital bone. Allows longitudinal growth. Fuses around 15-17 years.

Question 5

What is the cranial base angle and how does it affect face shape?

Answer 5

The angle between sphenoid and occipital bones.
Predicts the position of the mandible:
large angle associated wtih square jaws and overbites
small angle associated with wide angled mandibles and mandibular protrusion

Question 6

What type of cells converge in the pharyngeal arches?

Answer 6

Mesenchyme and neural crest cells

Question 7

What types of tissues do the cells in the pharyngeal arches produce?

Answer 7

Cranial nerves
Cartilage that may remain cartilage or ossify
Artery (aortic arch)

Question 8

What are the key nerve, muscle, and bony/cartilage structures associated with the mandibular arch?

Answer 8

CN V
Mandible, maxilla, zygoma, malleus, incus, squamous temporal
Muscles of mastication, anterior digastric, tensors tympani and palati

Question 9

What are the main pharyngeal arches?

Answer 9

Mandibular, hyoid, third, and fourth

Question 10

What are the key nerve, muscle, and bony/cartilage structures associated with the hyoid arch?

Answer 10

CN VII
Styloid process, hyoid, stapes
Muscles of facial expression, posterior digastric, stylohyoid, stapedius

Question 11

What are the key nerve, muscle, and bony/cartilage structures associated with the third arch?

Answer 11

CN IX
hyoid
stylopharyngeus

Question 12

What are the key nerve, muscle, and bony/cartilage structures associated with the fourth arch?

Answer 12

CN X
larynx
pharynx, larynx

Question 13

Describe the structures that arise from the pharyngeal grooves and pouches, including any migrations.

Answer 13

Grooves
1: external auditory meatus

Pouches

1: tympanic cavity & auditory tube
2: palatine tonsil
3: thymus and parathyroid glands, migrate down into the neck
4: parathyroid and C cells of thyroid, migrate down into the neck

Question 14

Describe the development and migration of the thyroid gland

Answer 14

Descends from the base of the tongue through foramen cecum and thyroglossal duct, around the front of the hyoid to its final position anterior to the larynx.

Question 15

What are the underlying developmental steps that lead to cleft lip and palate?

Answer 15

The face is formed by medial migration and fusion of maxillary, mandibular, nasomedial, and nasolateral processes.
Cleft lip arises due to failed fusion of maxillary and medial nasal prominences.
Cleft palate is due to failed fusion of palatine processes.