Head And Neck Embryology Flashcards
Viscerocranium bones are derived from what?
First 2 pharyngeal arches
The primordia
The naive head and neck
Neuroectoderm -> efferent nerve pathways
Neural crest cells -> mesenchyme
Preotic somitomeres
Superior to the otic vesicle
Differentiate into the muscles of the orbit and include CN3,4,6
Postotic somites
Generates the tongue tissue and muscles of the tongue as well as CN 12
Somatic mesenchyme
Generates accessory nerve (CN11)
Placodes
Thickening of the ectoderm in Locations that end up differentiating into special sensory functions
3 placodes
Olfactory placode = CN1/smell
Optic placode = CN2/vision
Otic placode = CN8/ hearing and balance
Endoderm
Derives the epithelial membranes over the middle ear, sinuses and oral/nasal cavities
Also generates pharynx and all glands/tonsils
Pharyngeal grooves vs pharyngeal pouches
Grooves = derived from ectoderm
Pouches = derived from endoderm
1st arch
Nerve = CN 5
Muscles = muscles of mastication, tensor muscles, mylohyoid anterior belly of the diagastric
Arteries = external carotid and maxillary
Bones = all intramembranous viscerocranium bones, Meckels cartilage (incus/malleus bones)
- breaks into a maxillary and Mandibular prominence with the only difference being bone development*
- maxillary = all other intramembranous Viscerocranium bones
- mandibular = mandible bone
2nd arch
Nerve = 7
Muscles = all muscles of facial expression, stylohyoid, stapedius, posterior diagastric
Artery = stapedial artery
Bone/cartilage = reichert cartilage (stapes, styloid process and superior portion of the hyoid)
3rd arch
Nerve = CN9
Muscles = stylopharyngeus only
Artery = internal and common carotid arteries
Bone/cartilage = inferior part of the hyoid bone
4th arch
nerve = CN10
Muscles = palatoglossus, palatopharyngeus, levator veli palatini, Salpingopharyngeus, cricothyroid and pharyngeal constrictors.
Cartilage = laryngeal cartilage (thyroid, laryngeal, crico cartilage, aretynoid cartilage)
Arteries = right subclavian, aorta and the aortic arch
6th arch
Nerve = recurrent laryngeal via (CN10)
Muscles = intrinsic muscles of the larynx only
Artery = right and left pulmonary arteries as well as the ductus arteriosus
Cartilage: same as 4th arch since they fuse
What generates the epiglottis
Fusion of mesenchyme from 3rd and 4th arches
1st grooves
Becomes the external auditory meatus
- the rest of the grooves become gills and 99% of the time obliterate*
1st pouch
Between the 1st and 2nd arches
Generates the tympanic membrane and cavity
2nd pouch
Between the 2nd and 3rd arches
Generates the palatine tonsils and foramen cecum
3rd pouch
Generates between the 3rd and 4th arches
Generates the inferior parathyroid glands and the the thymus
4th pouch
Forms between the 4th and 6th arches
Generates the superior parathyroid glands
Tongue development
Generates at the beginning of the 4th week as a lump in the anterior primordial pharynx just anterior to the foramen cecum
Lingual swellings diverticulate out from the 1st two arches forming the anterior two thirds tongue mucosa
- hence why CN5 and 7 do the anterior two thirds of the tongue
Copula and hypopharyngeal eminences form below the lingual swellings and form the posterior 1/2 of the tongue mucosa
- hence why CN9 does sensation and taste to the posterior 1/3 of the tongue and CN10 does sensation to the pharynx
Thyroid descent
Of of the 2nd arch, the thyroid normally generates a thyroglossal duct and a foramen cecum
The thyroid then moves down this duct to the larynx
