Head and Neck Neuroembryology

Question 1

head and neck derivatives of the ectoderm

Answer 1

neural tube (CNS motor neurons, preganglionic ANS), neural crest (PNS, post ganglionic ANS), epithelial skin, nasal pit, external ear, olfactory, lens, otic (from placodes)

Question 2

head and neck derivatives of the endoderm

Answer 2

epithelial lining (pharynx, larynx, trachea, esophagus, pharyngotympanic tube, middle ear), glands (thymus, parathyroid, tonsil, thyroid, mucosal)

Question 3

head and neck derivatives of the mesoderm

Answer 3

notochord (nucleus pulposus), somites that form bones, muscles, connective tissue, sclerotome (bone and cartilage), dermatome (dermis), myotome (muscles)

Question 4

neural crest derivatives related to the head and neck

Answer 4

PNS postganglionic autonomic nervous system, connective tissue and bone of face and skull, cranial nerve ganglia, skin of face, DRG, parasymapthic and sympathetic chain ganglia, adrenal medulla, schwann cells, satellite cells, meninges, melanocyte

Question 5

which aortic arch is vestigial and does not develop?

Answer 5

5th aortic arch

Question 6

what forms the auricle?

Answer 6

mesenchymal and condensations associated with the 1ST AND 2ND pharyngeal pouches

Question 7

which pharyngeal CLEFT forms the external auditory canal?

Answer 7

1st pharyngeal cleft

Question 8

which pharyngeal POUCH forms the pharyngotympanic tube and middle ear cavity?

Answer 8

1st pharyngeal pouch

Question 9

what lines the outside of the tympanic membrane? what lines the inside of the tympanic membrane?

Answer 9

ectoderm; endoderm; there is mesoderm in between.

Question 10

what do the pharyngeal arches develop from?

Answer 10

neural crest cells that proliferate and migrate around the sides of the developing pharynx

Question 11

how does the 2nd pharyngeal arch form the smooth skin over the neck?

Answer 11

it overgrows the 3rd and 4th pharyngeal clefts

Question 12

what is the cervical sinus? how does it form?

Answer 12

2nd, 3rd, 4th pharyngeal grooves merge to form it;

Question 13

where would a branchial cyst be located in the neck? is there a surface landmark that can be used to describe its location?

Answer 13

it would be located above the lateral part of the SCM muscle, between it and the larynx

Question 14

which cranial nerve innervates muscles derived from the 1st, 2nd, 3rd, 4th pharyngeal arches?

Answer 14

trigeminal (V), facial (VII), glossopharyngeal (IX), and vagus (X), respectively

Question 15

what are the skeletal derivatives from the 1st, 2nd, 3rd, 4th pharyngeal arch cartilages?

Answer 15

1st: malleus, incus
2nd: stapes, styloid process, superior half of hyoid (stylohyoid ligament)
3rd: inferior half of body and greater horn of hyoid
4th: thyroid, epiglottic cartilages

Question 16

where does the thyroid begin as an outpocketing of endoderm?

Answer 16

thyroid diverticulum (at the posterior edge of the 1st pharyngeal arch)

Question 17

what path does the thyroid take to migrate to its final resting position? what structure could you identify on a cadaver that marks this pathway?

Answer 17

from the foramen cecum, through thyrogossal duct, down in front of the hyoid bone; adams apple?

Question 18

what is a thyroglossal duct cyst? where would it be located?

Answer 18

it would be located at the foramen cecum where it meets the thyroglossal duct; protruding through the upper anterior neck.

Question 19

what are the derivatives of the 1st, 2nd, 3rd, 4th pharyngeal POUCHES?

Answer 19

1st pouch: pharyngotympanic tube, middle ear
2nd pouch: palatine tonsil (epithelial crypts)
3rd pouch: inferior parathyroid, thymus
4th pouch: superior parathyroid, ultimobranchial body

Question 20

what symptoms would a px display if glands developing from the 3rd pharyngeal pouch fail to develop properly?

Answer 20

hypocalcemia, recurrent infections due to T cell inadequacy

Question 21

which parts of the developing face form the upper and lower jaw?

Answer 21

1st pharyngeal arch has both maxillary and mandibular parts that form the upper and lower jaw regions respectively

Question 22

what parts of the face does the frontonasal process form?

Answer 22

philtrum, external nose

Question 23

the medial nasal swellings fuse to form what part of the developing face?

Answer 23

intermaxillary segment that will develop into the external nose, philtrum of upper lip and primary palate.

Question 24

where is the nasolacrimal groove located in the developing face? what two structures form its boundaries?

Answer 24

cleft between the lateral nasal swelling and the maxillary part of the 1st arch.

Question 25

what causes an oblique facial cleft?

Answer 25

failure of fusion of between the lateral nasal swelling and the maxillary process of the 1st arch.

Question 26

which three structures fuse to form the hard palate? does the intermaxillary segment contribute to the hard palate?

Answer 26

fusion of the primary palate, 2 secondary palates; yes the intermaxillary segment is the primary palate, and it contributes to the hard palate.

Question 27

how does a cleft lip form?

Answer 27

results from failure of the medial nasal and maxillary prominence to fuse

Question 28

how does a cleft palate form?

Answer 28

failure of the palatine processes to fuse with each other

Question 29

what develops fro occipital myotomes?

Answer 29

tongue muscles

Question 30

what structures fuse to form the anterior 2/3 of the tongue? which pharyngeal arch does this arise from?

Answer 30

lateral lingual swellings from the 1st pharyngeal arches fuse

Question 31

what structures fuse to form the posterior 1/3 of the tongue? does the 2nd pharyngeal arch contribute to any structures in the developing tongue?

Answer 31

2 caudal lingual swellings from the 3rd and 4th pairs of pharyngeal arches; 2nd pharyngeal arches are overgrown and only give rise to taste buds in the anterior 2/3 of the tongue.

Question 32

how many somites are formed during normal development? how many for each region of the adult vertebral column?

Answer 32

start with 42-44 pairs; some disappear and leave only 36-38 (3 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 3-5 coccygeal)

Question 33

describe the developmental event that causes spinal nerves to lie between vertebrae in the adult?

Answer 33

resegmentation: they end up at the level of the IV disk where they exit the vertebral column through the IV foramina

Question 34

what normal embryological process has been interrupted to cause the formation of a hemivertebrae?

Answer 34

defect of formation of the vertebral column

Question 35

what occurs if you do not have proper resegmentation of the developing vertebrae?

Answer 35

block vertebrae or bar vertebrae, or ‘unilateral bar and hemivertebrae’