2-Pharyngeal Arches

Question 1

development of arches

Answer 1

-4th week neural crest cells migrate into future head and neck
-core of mesenchyme, embryonic CT, lined externally by ectoderm and internally by endoderm
-arches visible by end of 4th week
-5th arch not develop in humans

Question 2

arch components

Answer 2

1. artery
2. cartilage
3. muscles
4. nerve

Question 3

first arch

Answer 3

1. maxillary A
2. trigeminal N (CN-V)
3. MASTMATT aka muscles of mastication, mylohyoid, anterior digastric, tensor tympani, tensor veli palatini
4. malleus, incus, maxillary, mandibular prominences

Question 4

second arch

Answer 4

1. artery regresses > stapedial and hyoid A
2. facial N (CN-VII)
3. muscles of facial expression, stapedius, stylohyoid, poster digastric, platysma
4. stapes, styloid process, lesser horn hyoid bone

Question 5

third arch

Answer 5

1. common carotid A and proximal internal carotid A
2. glossopharyngeal CN IX
3. stylopharyngeus
4. greater horn hyoid bone

Question 6

fourth arch

Answer 6

1. R side proximal R subclavian, L side aortic arch b/t L common carotid and L subclavian
2. vagus CN X
3. levator veli palatini, pharyngeal constrictors, proximal striated esophagus, intrinsic laryngeal, circothyroid
4. thyroid, cricoid, arytenoid, corniculate, cuneiforn cartilages

Question 7

first pharyngeal pouch

Answer 7

becomes tubotympanic recess > mastoid antrum, tympanic cavity, auditory tube

Question 8

second pouch

Answer 8

becomes palatine tonsillar sinus/fossa

Question 9

third pouch

Answer 9

descends to be inferior parathyroid glands, inferior portion thyroid gland, thymus, into superior mediastinum

Question 10

fourth pouch

Answer 10

becomes superior parathyroid gland and ultimopharyngeal body (fuses w/ thyroid) for parafollicular cells of thyroid gland

Question 11

pharyngeal grooves

Answer 11

1 persists and forms external auditory meatus

2,3,4 fuse to be cervical sinus then gets obliterated as neck develops
-if stays open externally then cervical fistula
-if sinus still there but closed off external then cyst

meatus meets with 1st pouch, ear drum b/t the two

Question 12

pharyngeal membrane

Answer 12

where pharyngeal grooves (ectoderm) meets pouch (endoderm)

tympanic membrane from first membrane

Question 13

thyroid gland

Answer 13

starts thyroid diverticulum @ base of developing tongue, foramen cecum
-descends ventrally in neck as thyroglossal duct
-lumen of duct obliterates as cells prolif when thyroid gets to base of neck, duct can stay in adult as pryamidal lobe of thyroid