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Embryology VI: Head/Neck development
11/25/2009 Nickalus Khan
Questions (1-92)
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Around what weeks do the Pharyngeal ridges develop?
What are these arches also called?
How many arches can we see externally in the developing embryo?
Which arch degenerates?
Pharyngeal arche mesenchyme consist of what type of germ tissue?
What tissue produces all of the muscles associated with the arches (branchiomeric
muscles)?
7. What produces skeletal structures associated with each arch?
8. What are the contents of a pharyngeal arch?
9. What is a pharyngeal arch covered with externally? Internally?
10. What artery is contained within each pharyngeal arch?
11. Each arch also has a ________ nerve within it.
12. What two processes does arch 1 contain?
13. What innervates each of these processes?
14. What bony structures are derived from the maxillary process?
15. What named cartilage is present within the mandibular process of the 1 st arch?
16. What does this cartilage give function as?
17. What does the posterior portion of this cartilage give rise to?
18. What is the musculature associated with the first arch?
19. What nerve is associated with the 2nd arch?
20. What named cartilage do the bony structures in the 2nd arch develop from?
21. What bony structures develop from this cartilage?
22. What musculature is associated with the 2nd arch?
23. What nerve is associated with arch 3?
24. What bony structures are formed from arch 3?
25. What nerve is associated with arch 4 and 6?
26. What cartilaginous structures are formed from arch 4?
27. What cartilaginous structures are formed from arch 6?
28. What are these cartilaginous structures derived from?
29. What is the nerve of the 4th arch?
30. What is the nerve of the 6th arch?
31. From what are the voluntary muscles of the tongue formed from?
32. From what are the voluntary musculature of the eye formed from?
33. What are the external invaginations of the pharyngeal arches called? What tissue are
they derived from?
34. What are the internal invaginations of the pharyngeal arches called? What tissue are
they derived from?
Embryology VI: Head/Neck development
11/25/2009 Nickalus Khan
35. What does cleft 1 form?
36. What do clefts 2-4 definitively form?
37. What is the only cleft that forms anything definitive?
38. What does pharyngeal pouch 1 form?
39. Endoderm that lines the auditory tube forms what?
40. What does the fibrous part of the eardrum come from?
41. What does pouch 2 form?
42. Tonsils lined with stratified squamous epithelium dip down into underlying tissue to
form what?
43. What is different about pouch 3 and 4 in comparison to pouch 1 and 2?
44. What does the dorsal wing of pouch 3 give rise to?
45. What does the ventral wing of pouch 3 give rise to?
46. What does the thyroid gland develop from?
47. What produces the secretory cells of the parathyroid glands?
48. Is the thymus supported by reticular fibers?
49. What forms the dorsal wing of pouch 4?
50. What forms from the ventral wing of pouch 4?
51. What is the function of the ultimobranchial body?
52. What is foramen cecum a landmark for?
53. What is a lateral cervical cyst?
54. Where are lateral cervical cysts usually found?
55. How is an external branchial fistula formed?
56. What is the typical opening of a branchial fistula?
57. What substance are neural crest cells sensitive to?
58. Treacher-collins syndrome and Robins syndrome both have what defining feature?
What arch defects are these two syndromes associated with?
59. What is the syndrome associated with 3rd pouch defects mentioned in lecture?
60. What are the defining feature(s) of DiGeorge syndrome?
61. What causes a thyroglossul cyst?
62. How is the tongue formed?
63. What part of the tongue do the lateral lingual swellings form?
64. What germ tissue are the lateral lingual swellings formed from?
65. What does the tuberculum impar form?
66. What does Arch 2 form in the tongue?
67. What arch forms the posterior 1/3 of the tongue?
68. What arch forms the base of the tongue?
69. What arch forms the voluntary muscles of the tongue?
70. How many prominences give rise to the face? Most are derived from?
Embryology VI: Head/Neck development
11/25/2009 Nickalus Khan
71. Which prominence is not from the first arch?
72. What are the prominences composed of?
73. Describe the beginning of formation of the nasal placode?
74. As the nasal pit forms what new prominences develop?
75. What does the frontonasal prominence form?
76. What does the medial nasal prominence form?
77. What does the lateral nasal prominence form?
78. What does the mandibular prominence form?
79. What does the maxillary prominence form?
80. What forms the intermaxillary segment?
81. Does maxillary bone come solely from maxillary process?
82. What forms the secondary palate?
83. What is the point where the palatine shelves fuse with the primary palate?
84. What causes a cleft lip?
85. What causes a cleft palate?
86. What forms the nasal cavity?
End of Class questions:
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Name the organ that arises from the same pharyngeal pouch as the thymus.
Where do the voluntary muscles of the tongue originate?
Describe the primary palate and name the structure from which it arises.
The anterior two thirds of the tongue are derived from which pharyngeal arch.
Cleft lip occurs when the ______ fails to fuse with the ______.
Lateral cervical cysts are commonly located____________.
Answers:
1. 4th or 5th
2. Branchial: due to the vestigial gill formation in our prehistoric ancestors [Definition of branchia:
gill: respiratory organ of aquatic animals that breathe oxygen dissolved in water]
3. 4 or 5
4. 5th
5. Paraxial or Lateral Plate mesoderm
6. Local Mesoderm
7. Neural crest cells
8. Artery, Nerve, Cartilagenous structure
9. Ectoderm, endoderm, respectively
Embryology VI: Head/Neck development
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11/25/2009 Nickalus Khan
The same #’d aortic arch (1-6)
Cranial
Maxillary and Mandibular process aka prominences
Maxillary and Mandibular divisions of [V]
Maxilla, Zygomatic bone, temporal bone (derived from neural crest cells)
Meckel’s cartilage
Organizing center around which the mandible develops from surrounding mesenchyme by
intramembranous ossification, Meckel’s cartilage itself disappears
undergoes endochondral ossification to form parts of ear (malleus, incus)
Muscles of mastication, mylohyoid m., anterior belly of digastric m., tensor tympani m. , tensor
palitini m.
[VII] Facial N.
Reichert’s cartilage
Lesser horn of hyoid bone, upper part of body of hyoid bone, styloid process, stapes
Muscles of facial expression, posterior belly of digastric m., stylohyoid m., stapedius m.
[IX], glossopharyngeal n.
Greater horn of hyoid bone, lower part of body of hyoid bone
Vagus N.
Upper part of thyroid cartilage of larynx
Lower part of thyroid cartilage and cricoid cartilage
Neural Crest cells
Superior Laryngeal N.
Recurrent Laryngeal N.
Upper occipital somites
Somiteomeres
Pharyngeal Clefts, ectoderm
Pharyngeal pouches, endoderm
External auditory meatus (the ectodermally derived epithelium aforementioned forms the
epithelial lining of the tympanic membrane)
Nothing, arch 1 overgrows them, initially they form an ectodermally derived cervical sinus which
later degenerates
1
Auditory tube (proximal portion), middle ear tube (distal portion)
Inner epithelial lining of the tympanic membrane
Mesoderm between the two epithelial linings
Palatine tonsil
Tonsilar crypts (endodermal in origin), endoderm invagination forms tonsilar fossa & rest of
tonsil comes from resident tissue (mesoderm)
Pouches 3 and 4 have a dorsal and ventral wing
Inferior parathyroids
Thymus
Embryology VI: Head/Neck development
11/25/2009 Nickalus Khan
46. invagination of pharynx [More detailed answer: Endoderm invaginates and a long duct grows
down from pharynx from which the thyroid develops, descends to its position in front of the
thyroid gland]
47. Endodermal tissue associated with the pouches
48. No, supported by a cytoreticulum which develops from the endodermal lining of pouch 3
49. Superior parathyroids
50. Ultimobranchial body
51. Forms C cells which secrete calcitonin, lowers calcium in the blood
52. Descent of the thyroid gland
53. Remnants of cervical sinus that can become inflamed and bulge in the neck
54. Anterior to SCM
55. Failure of 2nd pharyngeal arch to grow caudally and envelop the other pharyngeal arches,
produces a cyst communicating with the outside (thus the term fistula in the name)
56. Tonsilar fossa
57. Neural crest cells exhibit sensitivity to alcohol and retinoic acid [these cells are deficient in
superoxide dismutase and catalase which causes these cells to lack the ability to scavenge free
radicals cell damage]
58. Underdeveloped mandible, 1st arch defects
59. DiGeorge syndrome
60. Absence of thymus severe immunological deficiencies, absence of parathyroids,
cardiovascular defects (main problem), facial defects (short philtrum  fish mouth)
61. Thyroglossul duct is the invagination of endoderm that marks the descent of the thyroid gland
from the foramen cecum, a cyst anywhere along this migration (midline cyst) is termed a
thyrglossul cyst
62. Two lateral lingual swellings from Arch 1 fuse around a middle structure called the tuberculum
impar
63. Anterior 2/3
64. Ectoderm (recall V3 GSA sensory inn. to ant. 2/3 of tongue, GSA means ectodermally derived
tissue)
65. Nothing, it is overgrown by the lateral lingual swellings
66. Nothing definitive, evidence is left showing that the facial n. (2nd arch) played a part in
development (recall chorda tympanii and parasympathetic SA inn. to tongue for taste)
67. Arch 3, thus its inn. by [IX] for GSA and taste
68. Arch 4, thus inn. of vagus N. to base of tongue
69. No arch! They are derived from occipital somites
70. 5 [two maxillary, two mandibular, frontonasal], most derived from first arch
71. Frontonasal prominence (develops from bulging mesoderm at surface)
72. Mesoderm and neural crest cells
73. Thickening of ectoderm invaginates into deeper tissues to form a nasal pit
74. Medial and Lateral nasal prominence
75. Forehead and cranium, nasal septum, bridge of nose
Embryology VI: Head/Neck development
11/25/2009 Nickalus Khan
76. Philtrum of lip, tip of nose, part of maxillary process (i.e. maxilla with 4 incisor teeth and the
primary palate)
77. Ala of nose
78. Lower jaw and lip
79. Central face and upper lip, maxillary bone and some other related cranial bones
80. Medial nasal process
81. No, the medial nasal process gives rise to the intermaxillary segement which becomes a part of
the maxillary bone
82. Two palatine shelves from maxillary process that reach each other in the midline and fuse, nasal
septum grows down to meet them and the palate is formed
83. Incisive foramen
84. Failure of fusion of maxillary prominence to medial nasal prominence
85. Failure of palatine shelves to fuse with primary palate, or with each other
86. Thickening of ectoderm forms nasal pit, separated by oronasal membrane which degenerates &
forms communication between oral and nasal cavities, primitive choanae develop from behind
primary palate, secondary palatine shelves fuse and seal off oral cavity from nasal and put the
primitive choanae into their definitive position
Answers:
87.
88.
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90.
91.
92.
Inferior parathyroids
Occipital somites
Medial nasal prominence
1st
Maxillary prominence, medial nasal prominence
Anterior to SCM