Head And Neck Embryology

Question 1

Viscerocranium bones are derived from what?

Answer 1

First 2 pharyngeal arches

Question 2

The primordia

Answer 2

The naive head and neck

Neuroectoderm -> efferent nerve pathways

Neural crest cells -> mesenchyme

Question 3

Preotic somitomeres

Answer 3

Superior to the otic vesicle

Differentiate into the muscles of the orbit and include CN3,4,6

Question 4

Postotic somites

Answer 4

Generates the tongue tissue and muscles of the tongue as well as CN 12

Question 5

Somatic mesenchyme

Answer 5

Generates accessory nerve (CN11)

Question 6

Placodes

Answer 6

Thickening of the ectoderm in Locations that end up differentiating into special sensory functions

3 placodes

Olfactory placode = CN1/smell

Optic placode = CN2/vision

Otic placode = CN8/ hearing and balance

Question 7

Endoderm

Answer 7

Derives the epithelial membranes over the middle ear, sinuses and oral/nasal cavities

Also generates pharynx and all glands/tonsils

Question 8

Pharyngeal grooves vs pharyngeal pouches

Answer 8

Grooves = derived from ectoderm

Pouches = derived from endoderm

Question 9

1st arch

Answer 9

Nerve = CN 5

Muscles = muscles of mastication, tensor muscles, mylohyoid anterior belly of the diagastric

Arteries = external carotid and maxillary

Bones = all intramembranous viscerocranium bones, Meckels cartilage (incus/malleus bones)

• breaks into a maxillary and Mandibular prominence with the only difference being bone development*
• maxillary = all other intramembranous Viscerocranium bones
• mandibular = mandible bone

Question 10

2nd arch

Answer 10

Nerve = 7

Muscles = all muscles of facial expression, stylohyoid, stapedius, posterior diagastric

Artery = stapedial artery

Bone/cartilage = reichert cartilage (stapes, styloid process and superior portion of the hyoid)

Question 11

3rd arch

Answer 11

Nerve = CN9

Muscles = stylopharyngeus only

Artery = internal and common carotid arteries

Bone/cartilage = inferior part of the hyoid bone

Question 12

4th arch

Answer 12

nerve = CN10

Muscles = palatoglossus, palatopharyngeus, levator veli palatini, Salpingopharyngeus, cricothyroid and pharyngeal constrictors.

Cartilage = laryngeal cartilage (thyroid, laryngeal, crico cartilage, aretynoid cartilage)

Arteries = right subclavian, aorta and the aortic arch

Question 13

6th arch

Answer 13

Nerve = recurrent laryngeal via (CN10)

Muscles = intrinsic muscles of the larynx only

Artery = right and left pulmonary arteries as well as the ductus arteriosus

Cartilage: same as 4th arch since they fuse

Question 14

What generates the epiglottis

Answer 14

Fusion of mesenchyme from 3rd and 4th arches

Question 15

1st grooves

Answer 15

Becomes the external auditory meatus

• the rest of the grooves become gills and 99% of the time obliterate*

Question 16

1st pouch

Answer 16

Between the 1st and 2nd arches

Generates the tympanic membrane and cavity

Question 17

2nd pouch

Answer 17

Between the 2nd and 3rd arches

Generates the palatine tonsils and foramen cecum

Question 18

3rd pouch

Answer 18

Generates between the 3rd and 4th arches

Generates the inferior parathyroid glands and the the thymus

Question 19

4th pouch

Answer 19

Forms between the 4th and 6th arches

Generates the superior parathyroid glands

Question 20

Tongue development

Answer 20

Generates at the beginning of the 4th week as a lump in the anterior primordial pharynx just anterior to the foramen cecum

Lingual swellings diverticulate out from the 1st two arches forming the anterior two thirds tongue mucosa
- hence why CN5 and 7 do the anterior two thirds of the tongue

Copula and hypopharyngeal eminences form below the lingual swellings and form the posterior 1/2 of the tongue mucosa
- hence why CN9 does sensation and taste to the posterior 1/3 of the tongue and CN10 does sensation to the pharynx

Question 21

Thyroid descent

Answer 21

Of of the 2nd arch, the thyroid normally generates a thyroglossal duct and a foramen cecum

The thyroid then moves down this duct to the larynx