Lecture 6: pharyngeal Flashcards
start of bilateral pharyngeal apparatus development
4-5 weeks post fertilization
in a cranial to caudal sequence
4 pairs of temporary embryonic structures
- pharyngeal arches
- pharyngeal grooves (clefts)
- pharyngeal pouches
- pharyngeal membranes
pharyngeal arches
5 pairs of arches (5th arch almost never forms)
-mesenchymal core (paraxial mesoderm, neural crest cells, and lateral plate) lined on the outside by ectoderm and endoderm on the inside
pharyngeal grooves (clefts)
external aspect (ectoderm-epidermis)
pharyngeal pouches
4 well defined internal structures formed by outpockting of the endoderm
pharyngeal membranes
two layered structures of ectoderm and endoderm
each pharyngeal arch contains
- cartilagenous skeletal component (neural crest cell derived)
- connective tissue (neural crest cell derived) and muscle component (paraxial mesoderm)
- cranial nerve
- aortic arch artery
intramembranous bone formation
- bone develops in well vascularized mesenchyme
- absence of cartilage model
- develops flat bones of face and skull
intra cartilaginous (endochondral) bone formation
-bone formation in a pre-existing cartilage model (limb bones, weight bearing bones, and some bones of the pharyngeal apparatus)
2 prominence of the 1st pharyngeal arch
maxillary and mandibular
maxillary prominence
- cartilage: palatopterygoquadrate
- cartilage regresses and leaves no adult remnants
mandibular prominence
- large contribution to the face
- cartilage: meckel’s cartilage: leaves some adult structures
meckel’s cartilage gives rise to
-incus
-malleus
by endochondral ossification
perichondrium of meckel’s cartilage forms
- anterior ligament of the malleus
- sphenomandibular ligament
intramembranous in the maxillary prominence forms
- squamous portions of the temporal bone
- maxillary bone
- zygomatic bone
- palatine bone
- from mesenchyme derived from neural crest cells
intramembranous in the mandibular prominence forms
mandible
*from mesenchyme derived from neural crest cells
muscle components of the 1st pharyngeal arch
- 4 muscles of mastication
- tensor veli palatini and tensor tympani
- anterior belly of the digastric
- mylohyoid
nerve components of the 1st pharyngeal arch
- mandibular branch of the trigeminal nerve (CN5) supplies muscles
- sensory to the skin of the face is through the ophthalmic, maxillary, and mandibular branches of the trigeminal nerve (CN5)
2nd pharyngeal arch (hyoid arch) cartilage
reichert’s cartilage
endochondral ossification
reichert’s cartilage gives rise to
- stapes
- styloid process
- stylohyoid ligament
- lesser horn and upper body of the hyoid bone
muscle components of the 2nd pharyngeal arch
- muscles of facial expression
- stapedius
- stylohyoid
- posterior belly of the digastric
nerve components of the 2nd pharyngeal arch
facial nerve (CN 7)
3rd pharyngeal arch gives rise to
lower part of the body and greater horn of the hyoid bone
-endochondral ossification
muscle components of the 3rd pharyngeal arch
stylopharyngeus
nerve components of the 3rd pharyngeal arch
glossopharyngeal (CN 9)
4th and 6th pharyngeal arches
- merge together
- form the laryngeal cartilages from lateral plate mesoderm
- ossification does not occur in these cartilages
muscle components of the 4th and 6th pharyngeal arch
- muscles of the soft palate
- muscles of the pharynx
- intrinsic muscles of the larynx
- muscles of the upper esophagus
nerve components of the 4th and 6th pharyngeal arch
vagus nerve (CN10)
1st pharyngeal pouch
- forms a stalk like extension (tubotympanic recess)
- expands towards the 1st pharyngeal cleft (future external acoustic meatus)
- distal portion expands to form the epithelial lining of tympanic cavity, proximal narrow portions forms the auditory tube (eustachian tube)
- *tympanic ear cavity and auditory tube
2nd pharyngeal pouch
- endoderm proliferates and forms buds that extend into the mesenchyme
- buds infiltrated by lymphatic tissue
- part of the pouch remains as the palatine fossa
- *palatine tonsil
3rd pharyngeal pouch
dorsal region: **inferior parathyroid gland (secrete PTH)
ventral: stoma of the **thymus
4th pharyngeal pouch
dorsal region: **superior parathyroid gland
ventral region: **ultimobranchial body (cells derived from neural crest cells)
1st pharyngeal cleft
external acoustic meatus
1st pharyngeal membrane
tympanic membrane
tongue development begins
week 4 of development
tongue arises from
proliferation of endoderm (and mesenchyme) of the pharyngeal floor
-swellings give rise tot ehe mucous membrane (epithelium and CT) of the tongue
pharyngeal arch 1 (tongue)
forms anterior 2/3 of the tongue
- median swelling midline
- two lateral swellings
- fuse midline
terminal sulcus
location where the anterior and posterior portions of the tongue fuse
copula
formed by the endoderm and underlying mesenchyme of the 2nd arch
hypobranchial eminence
formed by the endoderm and underlying mesonchyme of the 3rd and 4th arches
which arch does not contribute to the mucosa of the adult tongue
2nd arch because the 3rd overgrows the 2nd
posterior 1/3 of the tongue
formed by the 3rd and 4th arch endoderm
innervated by CN9 and 10
muscles of the tongue arise from..
the myotomes of the occipital somites that migrate forward towards the developing tongue
innervated by the hypoglossal nerve (CN12) except the palatonglossus
