Lecture 38 - Pharyngeal arches Flashcards
What do the epiblast cells become after they replace hypoblast cells?
Endoderm
What are the two fates of the epiblast cells?
1) fill in between epiblast and hypoblast
2) replace hypoblast cells
What do epiblasts become when they fill in between the epiblasts and hypoblasts?
Intraembryonic mesoderm
What does the rest of the epiblast cells become who dont invaginate?
Ectoderm
What does the notochord cause in the ectoderm?
Neural plate
What are the two ridges that form in the neural plate?
Neural folds
Neural groove
What grows at the tips of the neural folds?
Neural crest cells
What do the growth of somites cause?
Lateral folding of the trilaminar disc
What causes crainocaudal folding of the trilaminar disc?
Longitudinal growth of cranial and caudal ends of the neural plate tube
What is the oropharyngeal membrane?
Separates the pharynx from the oral cavity
Where does the oropharyngeal membrane start out?
Cranial to the developing neural tube
Where are the pharyngeal arches located?
Paired bulges along the call of the developing pharynx
What is the outer surface of the arches made of?
Ectoderm
What is the inner surface of the pharyngeal arches?
Endoderm
What is the middle of the pharyngeal arches made from?
Mesenchyme from paraxial and lateral plate mesoderm and neural crest cells
What are the numbers of the arches?
1 - 2 - 3 - 4 - 6
What does the mesoderm from the pharyngeal arches become?
Muscles of the head
What do the neural crest cells of the pharyngeal arches become in the head?
Skeleton of the head and neck
What is the nerve for arch 1?
CN V - Trigeminal
What is the nerve for arch 2?
CN VII - Facial n.
What is the nerve for arch 3?
CN IX - Glossopharyngeal
What is the nerve for arch 4?
CN X - Cranial laryngeal
What is the nerve for arch 6?
CN X - Caudal laryngeal
What are the two parts of the first arch?
Maxillary
– and –
Mandibular
What is the cartilage of the first arch?
Meckel’s cartilage
What is the fate of the Meckel’s cartilage of the first arch?
Malleus
– and –
Incus
What does the mesenchyme from the neural crest cells of arch 1 become?
Bones of the mandible and lower face - via membranous ossification
What does the mesoderm derived mesenchyme of the first arch become?
Dermis of the face and muscles of the mandible and ear
What are the muscles innervated by the first arch?
Muscles of mastication
Tensor typani and tensor veli palatini
Skin of face
What does the cartilage of the second arch articulate with?
Dorsal edge articulates with meckel’s cartilage
What does the cartilage of the second arch become?
Cranial part of hyoid apparatus (Stylohyoid, epihyoid, ceratohyoid, and cranial part of basihyoid)
Stapes
What muscles come from the second arch?
Stylohyoideus and caudal digastric
Stapedius
Muscles of facial expression
What happens to some of the muscles of facial expression from the second arch?
Migrate to the arch 1 territory
What comes from arch 3?
Thyrohyoid and caudal portion of the basihyoid
Stylopharyngeus
What comes from arch 4?
Cartilages of the larynx
Cricothyroid and pharyngeal muscles
What comes from arch 6?
Intrinsic muscles of the larynx - except cricothyroid
What is the area between the pharyngeal archs called?
Externally - Clefts
Internally - Pouches
What many internal pouches are there?
4
How many external clefts are there?
1
What does the external cleft become?
External auditory canal
What does the first pharyngeal pouch become?
Tympanic cavity
– and –
Pharyngotympanic tube
What forms where the pouch and the cleft join?
Tympanic membrane
What does pouch 2 become?
Tonsils
What does pouch 3 become?
Glands
What does pouch 4 become?
C cells to the thyroid gland
What does the second arch form when it overgrows?
leaves pocket of tissue in the developing neck - cervical sinus
What happens when there is a failure in the cervical sinus degenerating?
Cervical cysts in adults
What happens when there is a failure in the fusing of arch 2 and distal lateral cervical tissue?
Result in fistulas that may connect to the cervical cysts
What is the primitive oral opening called?
Stomodeum
What are within the nasal placodes?
Nasal pits
What is the major characteristics of nasal pits?
Depression left in the middle of placode as surrounding mesenchyme proliferates
What is the origin of the incisive bone?
Intermaxillary segemnt - fused medial nasal prominences
What are the four regions of the tongue?
Lateral lingual swelling
Tuberculum inpar
Copula
Epiglottal swelling
What is made from arch 1?
Lateral lingual swellings
– and –
Tuberculum impar
What is the copula made from?
Arches 2, 3, and 4
What makes up the epiglottal swelling?
Arch 4
What are occipital somites?
Some mesoderm migrates in to teh developing tongue to produce the muscle and somite innervation is preserved
