Face and Neck Embryology

Question 1

What are the four components of each pharyngeal arch?

Answer 1

1. Core of mesoderm that becomes muscle or CT
2. Cartilage - neural crest derived; will become bone or cartilage
3. Artery aka aortic arch
4. Nerve - will become a cranial nerve

Question 2

What does the first pharyngeal cleft give rise to?

Answer 2

External auditory meatus

Question 3

What does the first pharyngeal membrane give rise to?

Answer 3

Tympanic membrane

Question 4

What does the first pharyngeal pouch become?

Answer 4

The lateral wall of the pouch (endoderm) becomes the inner surface of the tympanic membrane; the pouch itself eventually becomes the eustachian tube medially and the middle ear cavity laterally.

Question 5

What does the 2nd pharyngeal pouch become?

Answer 5

Lining of the crypts of the palatine tonsils

Question 6

What does the 3rd pharyngeal pouch give rise to?

Answer 6

Dorsal part –> inferior parathyroid glands

Ventral part –> thymus

Question 7

What does the 4th pharyngeal pouch give rise to?

Answer 7

Dorsal part –> superior parathyroid glands

Ventral part –> ultimopharyngeal/ultimobranchial bodies (these induce formation of parafollicular cells of the thyroid)

Question 8

DiGeorge syndrome is characterized by failure of development of the ____ and ____ pharyngeal pouches, leading to absence of…?

Answer 8

3rd, 4th pouches don’t develop –> no parathyroid glands, no thymus, no parafollicular cells of the thyroid

Question 9

Describe the possible anomalies seen when the first and second pharyngeal arches fail to develop properly, respectively.

Answer 9

1st:

Micrognathia

Cleft palate

Ear development problems

2nd:

Hypoplastic hyoid bone

Question 10

What do pharyngeal clefts 2 through 4 give rise to in the adult?

Answer 10

Trick question! Nothing; they form the cervical sinus, a transient space/structure in the fetus

Question 11

Name three anomalies that can occur as a result of abnormal cervical sinus development.

Answer 11

1. Branchial cyst
2. Branchial sinus
3. Branchial fistula

Question 12

Describe the location of brachial cysts with respect to the mandible and SCM.

Answer 12

Inferior to the angle of the mandible, anterior to the SCM

Question 13

Why is the innervation of the tongue so funky?

Answer 13

Because the tongue arises from the floor of the pharynx from pharyngeal arches 1 through 3. The tongue arising from the first arch overgrows the 2nd and becomes the anterior 2/3 of the tongue. This is why the corresponding nerves of the 1st and 2nd arches (CNs V and VII) innervate the anterior 2/3 of the tongue (general sensory and taste, respectively).

The posterior third of the tongue arises from the 3rd pouch, and its corresponding nerve (CN IX) innervates that part of the tongue (both taste and general sensory).

Question 14

The thyroid glands begins developing at the _______ ________ near the posterior part of the tongue. It descends the ________ _______ to its final location in the mediastinum.

Answer 14

begins development at the foramen cecum, travels down the thyroglossal duct to its final spot

Question 15

What is it called when the anterior part of the tongue fails to become mobile, resulting in a frenulum that connects to the anterior part of the tongue?

Answer 15

Ankyloglossia

Question 16

What is it called when the thyroid fails to migrate inferiorly and is stuck at the foramen cecum?

What is it called when a bit of the thyroglossal duct remains patent and forms a little bubble?

What is it called when pieces of thyroid get stuck in the neck?

Answer 16

Lingual thyroid

Thyroglossal duct cyst

Ectopic/accessory thyroid gland tissue

Question 17

Cleft lip occurs when the _______ ________ _______ fail to fuse at the midline.

Answer 17

Medial nasal prominences (to become the intermaxillary segment after fusion)

Question 18

The intermaxillary segment forms the ______ _______ directly behind the four insicors, anterior to the incisive canal.

Answer 18

primary palate

Question 19

The secondary palate forms from fusion of the ________ _______ of the maxilla. Failure of this to occur results in…?

Answer 19

palatal shelves

If they don’t fuse –> cleft palate

Question 20

Palatal clefts are classified into anterior cleft deformities and posterior cleft deformities. How are these defined?

Answer 20

Anterior deformities are those anterior to the incisive foramen, usually due to a problem w/ primary palate formation.

Posterior deformities are those that are posterior to the incisive foramen, usually due to a problem with secondary palate formation.

Question 21

What muscles are derivatives of the 1st pharyngeal arch (mandibular arch) and what cranial nerve derives from it?

Answer 21

Muscles of mastication

CN V (V2 & V3)

Question 22

Which muscles are derived from pharyngeal arch 2 (hyoid arch) and which cranial nerve developed from it?

Answer 22

Muscles of facial expression, CN VII (facial nerve)

Question 23

Which muscle(s) are derived from pharyngeal arch 3 and which cranial nerve developed from it?

Answer 23

Stylopharengeus (CN IX)

Question 24

Which muscle(s) are derived from pharyngeal arches 4 and 6 and which cranial nerve developed from those arches?

Answer 24

Muscles of soft palate (except tensor veli palatini), muscles of pharynx (except stylopharyngeus), cricothyroid, intrinsic muscles of the larynx

CN X