Head and Neck Embryology Flashcards
What are the 4 basic components to the pharyngeal apparatus?
arches
clefts
pouches
membranes
What are the three facial prominences?
frontonasal
maxillary
mandibular
What does the pharyngeal apparatus surround?
the developing foregut
How many pairs of arches are there?
5:
1st, 2nd, 3rd, 4th, 6th
What are the arches covered with externally and what are they covered with internally? What’s in the middle?
extoderm externally
mesenchyme in the middle
endoderm internally
How many pairs of clefts are there”
4
1st 2nd, 3rd and 4th
What are the pharyngeal clefts essentially?
they are surface ectoderm invaginations between the pharyngeal arches
How are the pouches different from the clefts?
clefts are external , pouches are internal
the pouches are endoderm lined areas along the lateral walls of the pharyngeal guts, located opposite the pharyngeal clefts
What do the pharyngeal membranes separate?
hte pouches from the clefts
they do NOT break down in humans, so the clefts and pouches don’t communicate ever (like they do in fish)
What are the three general cells types that migrate into the arches as they form?
mesoderm from somites and somitomeres
neural crest cells
nerves
Where does the mesoderm come from for the eye muscle precursors? For the tongue?
eyes - somitomeres
tongue - occipital somites
another term for neural crest cells is…
neuroectoderm
What are the 4 general elements found in each arch?
skeletal
muscular
neural (cranial nerves)
vascular (aortic arch arteries)
Each arch is supplied by a ___ cranial nerve
single
What CN is associated with the 1st arch?
trigeminal
What nerve is associated with the 2nd arch?
facial
What nerve is associated with the 3rd arch?
glossopharyngeal
What nerve is associated with the 4th arch?
vagus (internal branch ofthe superior larygenal)
What nerve is associated with the 6th arch?
vagus nerve (recurrent laryngeal)
What are the derivatibves of the first pharyngeal arch?
maxillary prominence becomes upper jaw
mandibular prominence becomes lower jaw
so you have maxilla, zygomatic bones, squamous part of temporal bone (intramemebranous oss)
malleus, incus (endochondral ossificaiton)
sphenomandibular ligament, sphenoid spine
What cartilage forms in the mandibular prominence and forms the sphenomandibular ligament and malleus and incus?
Meckel’s cartilage
What muscles are innervated by V3 in the 1st pharyngeal arch?
muscles of mastication
mylohyoid
anterior belly of digastric
tensor tympani
tensor veli palatini
Describe Treacher COllins Syndrome?
it’s First Arch Syndrome
you have a deficiency of neural crest cell migration intot he 1st arch
so you get mandibulofacial dystosis, abnormal development of the 1st arch structures, conductive hearing loss
completely normal brain function
What is Pierre Robin Syndrome?
Another first arch syndrome
deficiency of neural crest cell migration leads to micrognathia, large posteriorly placed tongue - leading to airway obstruction. Also cleft palate issues
What is the treatment for Pierre Robin Syndrome?
you use distraction osteogenesis to lengthen the mandible
sometimes you have to put in a tracheostomy to maintain airway
What cartilage develops in the second arch?
Reichert’s cartilage
What muscles are innervated by the facial nerve? (So what muscles are derived from the 2nd arch)
muscles of facial expression
posterior belly of digastric
stylohyoid
stapedius
What is the main skeletal derivative of the third arch?
the lower body of the hyoid bone (the upper body of the hyoid bone is form the 2nd arch)
What is the muscle derived from the third arch?
stylopharyngeus (only one innervated by the glossopharyngeal nerve)
What are the cartilages that form form the 4th and 6th arches?
the thyroid and cricoid cartilage
What are the derivatives of the first pouch?
the tubotympanic recess, which forms the auditory tube, middle ear cavity, and mastoid air cells
What is the main derivaitive of the second pouch?
palatine tonsils
What are the two glandular derivatives of the third pouch?
thymus
inferior parathyroid glands
(note they both have to immigrate downward)
What are the derivatives of the fourth pouch?
superior parathyroid glands and the ultimobranchial bodies that will become the parafollicular cells of the thyroid
What is the clinical implication of the fact that the 3rd and 4th pouch derivatives have to mgirate a ways?
you can get accessory or ectopic parathyroids and thymic tissue
What is DiGeorge Syndrome?
it’s a microdeletion of chromosome 22
you have no thymus or parathyroids (so diminished immunity and hypocalceumia)
it’s because you don’t get nerla crest migration intot he 3rd nand 4th pouch
also cleft palate, low set ears, hear defects, poor ciculation, poor muscle tone
What is the only cleft that has a derivative int he adult?
the 1st cleft - the external auditory meatus
DUring development, what is formed by the overgrown of the 2nd, 3rd, and 4th clefts by the 2nd arch?
the cervical sinus (lined with ectoderm)
it usually disappears
Clinically what will happen if the cervical sinus does not disappear?
You get a lateral cervical (branchial) cyst or fistula
What forms the thyroid gland? It’s kinda tricky.
It’s an endodermal evagination from the FLOOR of the pharynx between the 1st and 2nd arches.
so it actually kinda forms from gut
What is the site of origin for the thyroid gland then?
the foramen cecum of the tongue
What connects the tyroid to the tonuge during development?
the thyroglossal duct
If the thyroid doesn’t descend, what is it called?
a lingual thyroid
What is the only membrane to persist into adulthood? As what”
the 1st membrane persists as the tympanic membrane
What arhes are involved in tongue development?
1-4
What arch forms the anterior 2/3 of the tongue?
1st arch mesenchyme
Why does the 2nd arch ultmiatley not contribute tot he tongue?
It forms the copula, but it drops down and is overgrown by the 3rd arch
What marks the boundary between the anterior 2/3 and postieor 1/3 of the tongue? WHat memebrane used to be there?
the terminal sulcus
the buccopharyngeal membrane used to be there
What part of the tongue does the 4th arch contribute to them?
the epiglottis and extreme posterior tongue
Why are the tongue muscles tricky in terms of innervation?
they don’t stick with the arch-nerve rules
most of the tongue muscles are derived from myoblasts that migrate from the occipital myotomes with eh hypoglossal nerve, so that’s how they’re innervated
What’s the one muscle of the tongue not innervated by the hypoglossus?
palatoglossus - innervated by vagus
