H&N Embryology Flashcards
Pharyngeal/branchial apparatus
a group of structures that contribute to form head and neck Pharyngeal: 1) arches 2) pouches 3) grooves 4) membranes
Pharyngeal arches
paired ridges of tissue, each containing:
- muscle component
- cartilage
- CN
- aortic arch
Pharyngeal pouches
Paired segmented balloon-like pockets
separates pharyngeal arches internally
Pharyngeal grooves
paired clefts separating pharyngeal arches externally
Pharyngeal membranes
formed where epithelia of grooves and pouches approach each other
Arch formation
Each arch covered externally with ectoderm and internally by endoderm
6 arches formed during embryonic period but 5/6 are rudimentary (not visible on the surface of embryo)
Most of H/N congenital anomalies originate during transformation of pharyngeal apparatus into its adult derivatives
Neural crest cells
originate from neural tube
migrate into ventral part of pharyngeal arches and form different tissues
(Muscles and vascular endothelia are derived from original mesenchyme)
CT in the dorsal region of head
formed by paraxial mesoderm (somites, somatomeres)
1st pharyngeal arch name
mandibular arch - formation of the face
Portions of mandibular arch
Maxillary prominence
Mandibular prominence
Maxillary prominence derivatives
maxilla
zygomatic bone
squamous part of temporal bone
Mandibular prominence derivatives
mandible
1st arch syndrome
Insufficient migration of NCCs into 1st pharyngeal arch
Characteristics:
- deformed auricle of external ear
- defect in cheek between auricle and mouth
- hypoplasia of mandible
-macrostomia
SVE in H/N
muscles derived from pharyngeal arches
considered visceral, but can be controlled voluntarily
GVA in H/N
dermis and mucous membranes of H/N
CN V supplies
derivatives of 1st arch
sensory innervation of head and part of neck
motor innervation of muscles of mastication
CN VII supplies
derivatives of 2nd arch
CN IX supplies
derivatives of 3rd arch
Superior laryngeal branch of vagus nerve - supply
4th arch
CN X - supply
derivatives of 6th arch
Recurrent laryngeal branch of vagus nerve - supply
6th arch
1st arch cartilage
2 of middle ear ossicles
horse-shoe shaped primordium of mandible - guides its early morphogenesis
cartilage disappears as mandible develops around it by intramembranous ossification
2nd arch cartilage
Reichert cartilage
one of middle ear ossicles
styloid process of temporal bone
part of hyoid bone
3rd arch catilage
ossifies to form rest of hyoid bone that is not being formed by the 2nd arch
4/6th arch cartilage
fuse to form laryngeal cartilages (except for epiglottis - derived from mesenchyme of 3rd/4th arches)
Pharyngeal muscle innervation
CN X except stylopharyngeus (IX)
Soft palate muscle innervation
X
except tensor veli palatini (V3)
Tongue muscle innervation
XII except palatoglossus (X)
All tensor muscles in the head/neck innervation
tensor tympani/tensor veli palatini
V3
Laryngeal muscle innervation
Recurrent laryngeal nerve (X) except cricothyroid (superior laryngeal nerve X)
Anterior belly of digastric and mylohyoid muscle innervation
mylohyoid nerve (V3)
posterior belly of digastric and stylohyoid muscle innervation
VII
geniohyoid muscle innervation
C1
Strap (infrahyoid muscle) innervation
ansa cervicalis (C1,2,3)
Pharyngeal groove derivatives
at first: 4 grooves on each side of embryo
2nd arch grows and coveres 3/4
Separate pharyngeal arches externally
Only 1st pair of grooves remain –> external acoustic meatus
- other grooves lie in a slit-like depression = cervical sinus = normally obliterated as the neck develops
Cervical cysts - remnants of cervical sinus and/or 2nd groove may persist
Pharyngeal membranes derivatives
Appeared in floor of pharyngeal grooves during 4th week of development
Formed by conjunction of surface ectoderm with endoderm and intervening mesoderm
Only 1st pharyngeal membrane remains = tympanic membrane
1st pharyngeal pouch derivatives
tympanic membrane
tympanic cavity
auditory tube
2nd pharyngeal pouch derivatives
endodermal lining –> surface epithelium and lining of tonsilar crypt
mesenchyme around crypt –> lymphoid tissue, form lymphatic nodules of palatine tonsil
3rd pharyngeal pouch derivatives
inferior parathyroid glands and thymus
4th pharyngeal pouch derivatives
superior parathyroid glands and ultimopharyngeal (ultimobranchial) body
ultimopharyngeal (ultimobranchial) body fuses with thyroid gland –> cells give rise to parafollicular (or C) cells - produce calcitonin
- cells differentiate from NCCs that migrate from pharyngeal arches
Development of thyroid gland
1st endocrine gland to develop
Formed from a median endodermal thickening in floor of primordial pharynx and forms thyroid diverticulum
As tongue grows, developing thyroid descends, passing ventral to developing hyoid bone and laryngeal cartilages - still connected to the tongue by thyroglossal duct
After final stage: takes final shape in front of neck and thyroglossal duct degenerates and disappears
Proximal opening of thyroglossal duct persists as a small, blind pit –> foramen cecum of tongue
Thyroglossal duct cysts
Remnants of thyroglossal duct
tongue/anterior part of neck
painless, moveable median mass
cervical cyst is lateral, painless and moveable
Infection of a cyst–> perforation of skin, leading to a formation of a thyroglossal duct sinus
Ectopic thyroid gland
incomplete descent of thyroid gland –> sublingual thyroid gland appearing high in neck
Most common type: lingual hyroid glandular tissue
Development of anterior 2/3 of tongue
Oral part
Formed by fusion of lingual swellings on midline
swellings result from mesenchyme proliferation in 1st pharyngeal arch
Fusion of swellings indicated by median groove
Development of posterior 1/3 of tongue
Formed by 2 elevations caudal to foramen cecum
Early: mesenchyme of 2/3/4 arches take part
- end stage: mesenchyme of 2 disappears, develops from mesenchyme of 3/4
Tongue muscles derived from paraxial mesoderm of occipital somites - CN XII
Ant 2/3 tongue sensory
General: V3
Special: CN VII, chorda tympanic branch
Posterior 2/3 tongue sensory
CN IX for special and general
Foramen cecum sensory
CN X
1st arch derivatives
muscles of mastication
2 of middle ear ossicles
CN V2 and V3
2nd arch derivatives
Muscles of facial expression stapedius stylohyoid posterior belly of digastric 1 of middle ear ossicles, hyoid bone CN VII
3rd arch derivatives
Stylopharyngeus muscle
hyoid bone
CN IX
4/6 arches derivatives
soft palate muscles (except tensor veli palatini)
pharyngeal constrictor muscles
laryngeal muscles
cartilages of larynx
Superior and recurrent laryngeal branch of vagus (CN X)
