Pharyngeal Arch Development

Question 1

What structure do the neural crest cells form from?

Answer 1

Neural folds/dorsal neural tube

Question 2

What occurs during the fourth week of embryonic development? (4)

Answer 2

Neural folds meet and fuse = neural tube

Embryo folds along both rostral-caudal and dorsal-ventral axis = bean shape

Anterior end of neural tube rapidly expands to form beginnings of forebrain, midbrain and hindbrain

Continued development of somites

Question 3

What are rhombomeres?

Answer 3

Series of 8 bulges which make up the part of the neural tube which will form the hindbrain

Question 4

What happens to the anterior end of the neural tube (4th week)?

Answer 4

Expands rapidly as forebrain, midbrain and hindbrain form

Hindbrain region develops rhombomeres

Question 5

What happens to the mesoderm lateral to the expanding anterior neural tube?

Answer 5

Partially segments to form 7 somatomeres (rostrally, muscles of head and neck)

Fully segments to form somites (caudally, bones and muscles of back)

Question 6

How do the neural crest cells get to their arches?

Answer 6

Delaminate from dorsal neural tube

Migrate along specific pathways into their specific branchial/pharyngeal arches

Question 7

Where do the neural crest cells for the face and first branchial arch come from?

Answer 7

Midbrain and rhombomeres 1 and 2

Question 8

What do the neural crest cells which populate the facial region give rise to?

Answer 8

Facial ectomesenchyme which will undergo complex morphogenesis to form the face

Question 9

What are cranial neural crest cells required for in heart and artery development? (4)

Answer 9

Cardiac looping

Contraction of heart

Remodelling of aortic arches

Secondary heart field development

Question 10

What structures in heart and artery development are populated by neural crest cells? (2)

Answer 10

Conotruncal septum

Parasympathetic post-ganglionic neurons

Question 11

What is persistent truncus arteriosus?

Answer 11

No divide between pulmonary trunk and aorta

Question 12

What is a double outlet right ventricle?

Answer 12

Aorta connects to right ventricle instead of left

Question 13

What disorders can arise from poor neural crest cell function in heart and artery development? (4)

Answer 13

Persistent truncus arteriosus

Transposition of great vessels

Tricuspid stenosis

Double outlet right ventricle

Question 14

What syndromes can arise from poor neural crest cell function in heart and artery development? (2)

Answer 14

Digeorge syndrome

Charge syndrome

Question 15

What is the stomatodeum?

Answer 15

Primitive mouth - wide shallow depression in developing face

Question 16

When does the stomatodeum form?

Answer 16

When the frontal prominence develops

Question 17

Which branchial arch is called the mandibular arch?

Answer 17

First

Question 18

What limits the stomatodeum?

Answer 18

Buccopharyngeal membrane

Question 19

When do the pharyngeal arches and pouches appear?

Answer 19

4th and 5th weeks of development

Question 20

What are branchial arches?

Answer 20

Bars of mesenchymal tissue lined by ectoderm on the outside and endoderm on the inside

Contain cartilage, nerve and artery

Question 21

What separates different branchial arches?

Answer 21

Clefts (ectoderm)

Pouches (endoderm)

Question 22

How many pharyngeal arches are there and how are they numbered?

Answer 22

5

1, 2, 3, 4, 6

Question 23

What two structures do the branchial arches separate?

Answer 23

Stomatodeum and developing heart/cardiac bulge

Question 24

What makes up the mesenchyme of the branchial arches?

Answer 24

Neural crest cells

Mesoderm

Question 25

What do the tissues in the branchial arch mesenchyme generally give rise to? (2)

Answer 25

Neural crest cells - skeletal structures, ganglia, odontoblasts, connective tissues Mesoderm - endothelium and striated muscle

Question 26

Which nerve supplies the first branchial arch?

Answer 26

CNV trigeminal

Question 27

Which nerve supplies the third branchial arch?

Answer 27

CNIX glossopharyngeal

Question 28

Which nerve supplies the second branchial arch?

Answer 28

CNVII facial

Question 29

What does the first pharyngeal arch give rise to? (3)

Answer 29

Bones of lower two-thirds of face (maxilla and mandible) Meckel's cartilage Muscles of mastication

Question 30

What is formed from the first pharyngeal arch and what are their positions related to the stomatodeum? (2)

Answer 30

Maxillary process/palatopterygoquadrate - dorsal and lateral to stomatodeum Mandibular process - ventral and inferior to stomatodeum

Question 31

What does the maxillary process give rise to? (4)

Answer 31

Structures of maxilla and palate: - Maxillary bone - Premaxillary bone - Zygomatic bone - Squamous part of temporal bone

Question 32

Where is Meckel's cartilage initially found?

Answer 32

Within mandibular process

Question 33

How are the mandibular bone and Meckel's cartilage linked?

Answer 33

Mandibular bone forms by ossification of mesenchymal tissue of Meckel's cartilage

Question 34

What are the remnants of Meckel's cartilage in adults? (2)

Answer 34

Incus and malleus of inner ear Perichondrium of sphenomandibular and sphenomalleolar ligaments

Question 35

What muscles does the first branchial arch give rise to?

Answer 35

Muscles of mastication

Question 36

Which branchial arch is called the hyoid arch?

Answer 36

Second

Question 37

What cartilage is present in the second pharyngeal arch?

Answer 37

Hyoid/Reichert's cartilage

Question 38

What is derived from the second branchial arch? (4)

Answer 38

Stapes Styloid process on base of skull Lesser horns and upper part of hyoid bone Muscles of facial expression

Question 39

What muscles does the second branchial arch give rise to?

Answer 39

Muscles of facial expression

Question 40

What is derived from the third pharyngeal arch? (2)

Answer 40

Greater horns and lower part of hyoid bone Stylopharyngeus muscle

Question 41

What part of the third pharyngeal arch forms the greater horns and lower part of the hyoid bone?

Answer 41

Cartilage

Question 42

What occurs during the 5th and 6th weeks of development (first arch)? (3)

Answer 42

Bilateral maxillary processes fuse with medial nasal process to form the upper lip, alveolus and primary palate Lateral nasal processes form the alar/alae structures of the nose Lower lip and jaw formed by the mandibular process

Question 43

What is the primary palate?

Answer 43

Extension of intermaxillary process

Question 44

When is the secondary palate complete?

Answer 44

10th week

Question 45

How is the secondary palate formed and when? (3)

Answer 45

Palatine shelves grow medially from the maxillary prominences (late 7th/8th week) Initially palatine shelves grow beneath tongue but soon move upwards to meet at midline above tongue Fuse with each other and nasal septum

Question 46

When and what causes the separation of the left and right nasal chambers?

Answer 46

Growth of nasal septum as secondary palate is forming (late 7th/8th week)

Question 47

How does the fusion of the palatine shelves differ between males and females?

Answer 47

Occurs one week earlier in males

Question 48

What is the incisive foramen?

Answer 48

Where the primary and secondary palate meet

Question 49

What is a cleft palate ultimately caused by?

Answer 49

Failure of palatine shelves to fuse properly during 7th-10th weeks of development

Question 50

How many cases of cleft palate is also associated with a cleft lip?

Answer 50

50%

Question 51

What can cause a cleft palate? (4)

Answer 51

Inadequate growth of palatine shelves Failure of shelves to erupt above tongue Excessively wide head Failure to fuse secondary rupture after fusion

Question 52

What are some of the types of cleft lips/palates? (4)

Answer 52

Uni/bilateral cleft lip Uni/bilateral cleft palate Cleft uvula Uni/bilateral cleft lip and full/anterior cleft palate

Question 53

What is another name for mandibulofacial dysostosis?

Answer 53

Treacher-Collins syndrome

Question 54

What is another name of Treacher-Collins syndrome?

Answer 54

Mandibulofacial dysostosis

Question 55

What characterises Treacher-Collins syndrome? (2)

Answer 55

Under-developed facial bones Very small lower jaw and chin (micrognathia)

Question 56

What is another name for acrofacial dysostosis?

Answer 56

Nager syndrome

Question 57

What is another name of Nager syndrome?

Answer 57

Acrofacial dysostosis

Question 58

What characterises Nager syndrome? (4)

Answer 58

No angle between neck and chin - Bilateral mandibular hypoplasia and severe micrognathia and retrogenia Often a cleft palate Prominent forehead Possible cardiovascular and/or genitourinary abnormalities

Question 59

What are two syndromes caused by first pharyngeal arch abnormalities?

Answer 59

Nager syndrome Treacher-Collins syndrome

Question 60

What is another name for hemifacial microsomia? (2)

Answer 60

Ocular Auricular Vertebral Spectrum Oto-mandibular syndrome/dysostosis

Question 61

The derivatives of which arches are affected in hemifacial microsomia?

Answer 61

First and second

Question 62

What derivatives of the first branchial arch can be affected in hemifacial microsomia? (7)

Answer 62

Ramus Mandibular condyle TMJ Maxilla Masticatory muscles Oral commissure Ear

Question 63

What is the temporo-masseter sling and in what condition might you find it?

Answer 63

Temporal muscles and masseter muscles fused Hemifacial microsomia

Question 64

What will abnormalities in the facial nerve in hemifacial microsomia affect?

Answer 64

Mimic musculature

Question 65

What lines pharyngeal clefts?

Answer 65

Ectoderm

Question 66

Which pharyngeal cleft forms a structure in the adult and what is this structure called?

Answer 66

First cleft External auditory tube

Question 67

What happens to the pharyngeal clefts during development and when? (3)

Answer 67

3rd month - ectoderm at bottom of cleft proliferates to create meatal plug 7th month - plug disintegrates All clefts other than first are obliterated by caudal expansion of second arch creating the lateral cervical sinus

Question 68

What can remnants of pharyngeal clefts result in? (2)

Answer 68

Cysts with/without fistulas Facial nerve damage

Question 69

What lines pharyngeal pouches?

Answer 69

Endoderm

Question 70

How many of the pharyngeal pouches form structures in the adult?

Answer 70

All of them

Question 71

What does the first pharyngeal pouch give rise to?

Answer 71

Auditory tube and middle ear cavity

Question 72

What does the second pharyngeal pouch give rise to?

Answer 72

Numerous infoldings that become the crypts of the palatine tonsils

Question 73

What does the third pharyngeal pouch give rise to?

Answer 73

Divides into superior/dorsal and inferior/ventral Superior/dorsal - inferior parathyroid glands Inferior/ventral - thymus (epithelial reticular cells)

Question 74

What does the fourth pharyngeal pouch give rise to?

Answer 74

Divides into superior/dorsal and inferior/ventral Superior/dorsal - superior parathyroid glands Inferior/ventral - "fifth pharyngeal pouch" incorporated into thyroid to form parafollicular cells

Question 75

What forms the "fifth pharyngeal pouch"?

Answer 75

Inferior/ventral division of fourth pharyngeal pouch

Question 76

What nerves supply the tongue and which parts of it? (4)

Answer 76

CNV trigeminal for sensory receptors CNVII facial for taste buds CNIX glossopharyngeal for sensory receptors and taste buds CNX vagus for palatoglossus muscle

Question 77

What is the hypoglossal CNXII derived from?

Answer 77

Occipital somites

Question 78

What are the 2 mesodermal origins of the tongue?

Answer 78

Somites Hypoglossal cord (migratory cells)

Question 79

What is the common name of ankyloglossia?

Answer 79

Tongue tie