Embryology of Head & Neck

Question 1

Explain what derives from the first pharyngeal arch.

Answer 1

Neuroectoderm - CN V, mandibular n.
Mesoderm (Muscles) - MAST MATT
Mesoderm (Aortic Arch) - 0
Neural Crest - [ANT facial skeleton] Malleus & Incus (Middle Ear), Mandible, Maxilla, Zygomatic, Temporal (partially)

Question 2

Explain what derives from the second pharyngeal arch.

Answer 2

Neuroectoderm - CN VII, facial n.
Mesoderm (Muscles) - muscles of facial expression, stapedius, stylohyoid, posterior digastric
Mesoderm (Aortic Arch) - 0
Neural Crest - Stapes, Styloid Process (Temporal), Hyoid Bone (lesser horn, upper body)

Question 3

Explain what derives from the third pharyngeal arch.

Answer 3

Neuroectoderm - CN IX, glossopharyngeal n.
Mesoderm (Muscles) - stylopharyngeal m.
Mesoderm (Aortic Arch) - R & L common carotid, R & L internal carotid
Neural Crest - Hyoid Bone (greater horn, lower body)

Question 4

Explain what derives from the fourth pharyngeal arch.

Answer 4

Neuroectoderm - CN X, superior laryngeal branch
Mesoderm (Muscles) - soft palate muscles & pharyngeal muscles (5/6)
Mesoderm (Aortic Arch) -
[R arch] R. subclavian
[L arch] aortic arch
Neural Crest - thyroid cartilage

Question 5

Explain what derives from the sixth pharyngeal arch.

Answer 5

Neuroectoderm - CN X, recurrent laryngeal branch
Mesoderm (Muscles) - laryngeal & striated esophageal muscles
Mesoderm (Aortic Arch) - R & L pulmonary arteries, [L arch] ductus arteriosus
Neural Crest - laryngeal cartilage

Question 6

What develops from pharyngeal pouches?

Answer 6

The pharyngeal pouches (endoderm):
1 - Epithelial lining of auditory tube & middle ear cavity
2 - Epithelial lining of crypts of palatine tonsils
3 - Inferior parathyroid gland & thymus
4 - Superior parathyroid & ultimobranchial

Question 7

How are the pharyngeal pouches & grooves numbered?

Answer 7

Arch 1
Pouch/Groove 1
Arch 2
Pouch/Groove 2
Arch 3
Pouch/Groove 3
Arch 4
Pouch/Groove 4
Arch 6

Question 8

Describe the migrations of structures from pouch 3 & pouch 4

Answer 8

The components of pouch 3 migrate to the posterior-inferior pole of thyroid (PT gland) and below thyroid (thymus).

The components of pouch 4 migrate to the posterior-superior pole of thyroid (PT gland) and then into the thyroid gland to form the parafolicular (C) cells.

DiGeorge Syndrome involves the faulty migration of these two pouches.

Question 9

What develops from pharyngeal cleft/groove?

Answer 9

The pharyngeal grooves (ectoderm):
1 - External auditory meatus
2/3/4 - Lateral cervical sinuses along medial-anterior border of SCM (can lead to lateral cervical cysts)

Question 10

What develops from the mesoderm of the upper occipital somites?

Answer 10

The seven muscles of the orbit (CN III, IV, VI)

The muscles of the tongue (XII) sans paltoglossus

Question 11

Explain first arch syndrome and its symptoms.

Answer 11

Results from abnormal formation of pharyngeal arch 1 because of faulty migration of neural crest cells, causing facial anomalies (Treacher Collins syndrome and Robin sequence).

Question 12

Explain the formation of the thyroid gland.

Answer 12

Develops from endoderm thickening in at midline boundary of ANT ⅔ & POST ⅓ of tongue (foramen cecum is the remnant of this thyroglossal duct).

The thyroglossal duct breaks down as the thyroid gland forms.

Question 13

What are potential problems are created due to an ectopic thyroid gland?

Answer 13

Thyroglossal cysts - most frequently found in the superior hyoid region, but could also be found around body of tongue, INF to hyoid bone, or ANT to thyroid cartilage.

Question 14

Explain the development of the tongue.

Answer 14

Pharyngeal Arch 1 & 2 form the ANT ⅔ of the body of the tongue (tip of the tongue to terminal sulcus - circumvallate papillae)

Pharyngeal Arch 3 forms the POST ⅓ of the body of tongue, root of the tongue, and the palatine tonsils

Pharyngeal Arch 4 forms the epiglottis

Question 15

What are the five facial prominences and from what arch do they derive?

Answer 15

All from Arch 1:
One frontonasal prominence (also med/lat nasal promin.)
Two maxillary prominences
Two mandibular prominences

Question 16

What is the upper lip formed from?

Answer 16

The philtrum is made by the medial nasal prominence (of frontonasal) and the two maxillary prominences form the remaining upper lip.

Question 17

What does the frontonasal prominence form?

Answer 17

The frontonasal prominence forms the forehead, cranium, and bridge of nose.
The medial nasal prominence forms the philtrum and tip of nose.
The lateral nasal prominence forms the ala of the nose.

Question 18

What do the maxillary prominences form?

Answer 18

The maxillary prominence forms the central face, lower eyelid, and part of upper lip.

Question 19

The mandibular prominence forms what?

Answer 19

The mandibular prominence forms the lower jaw and lip.

Question 20

What are the two sources that form the hard palate?

Answer 20

The hard palate forms from two sources:

1. Intermaxillary segment (primary palate, four incisor teeth) from medial nasal prominences
2. Palatine shelves (secondary palate) from maxillary processes

Question 21

What leads to cleft lip and cleft palate?

Answer 21

Cleft lip occurs when the maxillary prominence fails to fuse with the medial nasal prominence.

Cleft palate occurs when the primary plate and secondary plate do not fuse at the midline. It could be bilateral, unilateral, and could involve the uvula.