embryology of the head and neck

Question 1

when do the pharyngeal arches develop in humans?

Answer 1

Arch 1 – Day 22
Arch 2 + 3 – Day 24
Arch 4 + 6 – Day 29

Question 2

what are the 3 components of the pharyngeal apparatus?

Answer 2

Core pharyngeal arch (Mesenchymal tissue)
External pharyngeal cleft (Ectoderm)
Internal pharyngeal pouch (Endoderm)

Clefts and pouches separate arches

Question 3

what does each pharyngeal arch consist of?

Answer 3

Core of mesenchyme derived from paraxial and lateral plate mesoderm
-Musculature

Neural crest cells
-Connective tissues
-Smooth muscle

Cranial nerve component
-Innervation (sensory or motor)

Artery (Aortic arch arteries)
-Review CVS embryology

Question 4

what are the skeletal derivatives of the first arch?

Answer 4

Maxillary process (cranial portion)
-Maxilla
-Zygomatic bone

Mandibular process (caudal portion)
-Forms Meckel’s cartilage
-Incus and Malleus (ear ossicles)
-Mandible
-Squamous portion of temporal bone

Question 5

what are the skeletal derivatives of the 2nd arch?

Answer 5

Stapes
Styloid process of temporal bone
Stylohyoid ligament
Lesser horn of Hyoid
Upper part of Hyoid body

Question 6

what are the skeletal derivatives of the third arch?

Answer 6

Greater horn
Lower part of hyoid bone

Question 7

what are the skeletal derivatives of the 4th-6th arches?

Answer 7

laryngeal cartilages

Question 8

what are the neural derivatives of the 1st arch?

Answer 8

Trigeminal nerve (CN V)

Maxillary (V2) and Mandibular (V3) divisions

Question 9

what is the neural derivatives of the second arch?

Answer 9

facial nerve

Question 10

what is the neural derivative of the 3rd arch?

Answer 10

glossopharyngeal nerve

Question 11

what is the neural derivative of arches 4-6?

Answer 11

vagus nerve

Question 12

what are the muscular derivatives of the 1st arch?

Answer 12

All Musculature supplied by CN V3:
-Muscles of mastication
-Anterior belly of digastric
-Mylohyoid
-Tensor tympani
-Tensor veli palatini

Question 13

what are the muscular derivatives of the 2nd arch?

Answer 13

All Musculature supplied by CN VII:
-Muscles of facial expression
-Posterior belly of digastric
-Stylohyoid
-Stapedius
-Auricular muscles

Question 14

what are the muscular derivatives of the 3rd arch?

Answer 14

All Musculature supplied by CN IX:
-Stylopharyngeus

Question 15

what are the muscular derivatives of the 4th-6th arch?

Answer 15

All Musculature supplied by CN X:
Levator veli palatini
Salpingopharyngeus
Palatoglossus
Palatopharyngeus
3 pharyngeal constrictors
Cricothyroid

intrinsic muscles of the larynx- 6th arch

Question 16

what does the 1st pouch form?

Answer 16

Tympanic membrane
Middle ear
Eustachian tube

Question 17

what does the 2nd pouch form?

Answer 17

palatine tonsil

Question 18

what does the 3rd pouch form?

Answer 18

Inferior parathyroid gland
Thymus

Question 19

what does the 4th pouch form?

Answer 19

Superior parathyroid gland
Ultimobranchial body
(Thyroid gland/C-cells)

Question 20

how does the tongue develop?

Answer 20

Usually appears in the 4th week by
-Two lateral swellings
-One midline swelling

Then formation of more midline swellings, copula and epiglottal.

Anterior mucosa derived from CN V3

Posterior mucosa derived from CN IX

Myoblasts originate from occipital somites and receive innervation from CN XII.

Question 21

which facial structures are derived from pharyngeal arch 1?

Answer 21

Maxilla, Mandible, Zygomatic and Temporal (Squamous part) bones
Muscles of Mastication

Question 22

which facial structures are derived from arch 2?

Answer 22

muscles of facial expression

Question 23

what are the 5 facial swellings present from week 4?

Answer 23

Frontonasal prominence (with nasal placodes)
Maxillary prominence (x2)
Mandibular prominence (x2)

Question 24

what are the 4 additional swellings present from week 5?

Answer 24

Medial nasal swellings (x2)
Lateral nasal swellings (x2)

Question 25

what are the features of the nasolacrimal grove?

Answer 25

Lies between the maxillary prominence and the lateral nasal prominence
Solid epithelial cord in floor of groove
Cord detaches from the ectoderm
Canalization forms the nasolacrimal duct

form at 7 weeks

Question 26

which components of the face form at 10 weeks?

Answer 26

Upper lip
-2 medial nasal prominences
-2 maxillary prominences

Lower lip
-Mandibular prominences

Nose
Frontonasal prominence
-Bridge and nasal septum
Medial nasal prominences
-Crest and tip
Lateral nasal prominences
-Alae (sides)

Question 27

how does the primary palate form?

Answer 27

Fusion of medial nasal prominences give: Intermaxillary segment

Question 28

how does the intermaxillary segment of the palate form?

Answer 28

Labial portion -> Philtrum of upper lip
Upper jaw component -> Carries 4 incisors
Palatal component -> form primary palate

Question 29

how does the nasal cavity develop?

Answer 29

5th week:
Nasal pits deepen and penetrate into the underlying mesenchyme with forward growth of frontonasal prominence

6th week:
As the intermaxillary segment forms it is connected by a nasal fin.
Nasal fin vacuolizes and thins, this opens the developing nasal sac.

7th week:
Nasal cavities communicate with oral cavity via Primitive choanae behind primary palate
Definitive choanae open at junction of nasal cavity with pharynx due to formation of secondary palate

Question 30

how does the secondary palate develop?

Answer 30

Right and left palatal shelves develop parallel to the tongue.
Fused in the central region initially then expands anteriorly and posteriorly.
Mandibular development facilitates clearance of the tongue