Orofacial Embryology

Question 1

branchial refers to…

Answer 1

gills- eventually the precursor for neck and lower 2/3 of face like mouth ear and neck

Question 2

4 components of pharyngeal apparatus

Answer 2

1. arches- bulge outward from neck region
2. cleft/groove- external invagination b/w arches
3. pouch- internal invagination b/w arches
4. membrane- tissue separating cleft and pouch

Question 3

when and where do the arches arise

Answer 3

week 4, cranial to caudal
1,2,3,4,6

give rise to lower 2/3 of face, oral cavity, ear, neck

Question 4

3 layers of arches

Answer 4

1. external- from ectoderm
2. filling/core- from mesoderm and neural crest, neural crest must migrate into arches for proper skeletal tissue formation
3. internal- from endoderm, forms GI tract lining

Question 5

innervation of the 5 arches

Answer 5

1=5
2=7
3=9
4=10
6=10

Question 6

5 areas that give rise to the face

Answer 6

frontonasal process and 2 maxillary processes and 2 mandibular processes

meet at the mouth eventually

Question 7

arch 1 gives rise to… (bones)

Answer 7

lower 2/3 of face- skin, muscle, bone

bone:
- maxillary process, forms that bone, palate, zygomatic, squamous temporal
- lower jaw, mandibular process: mandible, sphenoid spine, malleus, incus
- sphenomandibular ligament, anterior ligament of malleus

Question 8

what is meckel cartilage

Answer 8

origin of mandibular process of arch 1

Question 9

arch 1 muscle derivatives

Answer 9

muscle: all innervated by CN5, muscles of mastication

- mylohyoid, masseter, temporalis, anterior digastric, tensor tympani, tensor veli palatini

Question 10

formation of lower lip and jaw

Answer 10

arch 1 mandibular processes fusing at midline, rare anomalies

Question 11

formation of upper lip and jaw

Answer 11

more common- 3 areas are fusing

2 maxillary processes fusing w/ medial nasal process (philtrum)

anomolies more common, cleft lip and palate

Question 12

difference b/w cleft lip and palate, incomplete vs complete

Answer 12

cleft lip: clefting anterior to incisive foramen (meeting of processes)

cleft palate: clefting posteriror to foramen

incomplete- partial lack of fusion
can be unilateral or bilateral

Question 13

skeletal derivatives of arch 2

Answer 13

aka hyoid arch

starts w/ reichert cartilage- forms lesser horn of hyoid, stylohyoid ligament, styloid process, stapes

Question 14

muscles from arch 2

Answer 14

all from CN7

muscles of facial expression- posterior digastric, stylohyoid, stapedius

Question 15

skeletal derivatives of arch 3

Answer 15

starts w/ cartilage, forms body and greater horn of hyoid

Question 16

muscles from arch 3

Answer 16

from CN 9

stylopharyngeus

Question 17

skeletal derivative of arch 4,6

Answer 17

from cartilage- laryngeal cartilage (cricoid, thyroid, arytenoids, etc)

Question 18

muscles from arch 4,6

Answer 18

all from CN10

arch 4: pharyngeal constrictors, cricothyroid, levator veli palatini

arch 6: all laryngeal except cricothyroid

Question 19

describe phayngeal arch vasculature and what they become

Answer 19

each arch as 1 artery called aortic arch

1,2,5 disappear

3=common carotid
4= right subclavian and arch of aorta
6= pulm arteries

Question 20

arch contribution to the tongue

Answer 20

arch 1: anterior 2/3 (CN5 for somatic, 7 for taste)

arch 3: posterior 1/3 (CN9 for somatic and taste)

arch 4: base and epiglottis (CN 10 for both)

think cranial to caudal

Question 21

what happens to branchial clefts

Answer 21

2-4 disappear as arch 2 covers them up, temporarily creates cervical sinus

cleft 1 becomes external acoustic meatus- from ectoderm

Question 22

what is a branchial cleft cyst

Answer 22

persistent cervical vesicle/sinus

along anterior border of SCM muscle

Question 23

derivatives of 4 pouches

Answer 23

note these are internal, endoderm

1. eustachian tube
2. palatine tonsil
3. thymus, inferior parathyroids
4. superior parathyroids

Question 24

etiology of diGeorge syndrome

Answer 24

abnormal development of pouch 3 and 4- lack of thymus and parathyroids causes immune deficiency, hypocalcemia, facial/palate problems

Question 25

derivatives of branchial membranes

Answer 25

2-4 disappear under arch 2 overgrowth

1 becomes tympanic membrane (pouch 1 was eustachian tube)

Question 26

describe formation of ear, preceding structures (4)

Answer 26

arch 1,2: auricle

cleft 1: external accoustic meatus

membrane 1: tympanic membrane

pouch 1: eustachian tube

Question 27

list some facial characteristis of fetal alcohol syndrome

Answer 27

small head, low nose, thin upper lip, small eye openings

some due to neural crest cell injury or impaired migration