Week 8: Craniofacial Embryology Flashcards
when do head and neck develop and from what?
weeks 4-8; from pharyngeal or branchial apparatus
3 components of pharyngeal apparatus
- arches, clefts, and pouches
* 5 pairs of arches forms starting on day 22
pharyngeal clefts are made from what germ layer?
ectoderm
pharyngeal pouches are made from what germ layer?
endoderm
structure of each pharyngeal arch
outer ectoderm, inner endoderm, and core of mesenchyme -> mesoderm and neural crest
The neural crest portion of the pharyngeal arches form
cartilage, CT, and an arch-associated nerve
The mesoderm portion of the pharyngeal arches form
skeletal muscle and an artery
2 components of 1st pharyngeal arch
- maxillary process
* mandibular process
Maxillary process of 1st arch forms
maxilla and zygomatic bones
mandibular process of 1st arch forms
mandible and Meckel’s cartilage
what does Meckel’s cartilage become?
the incus and malleus of the middle ear
muscle derived from the 1st arch
- muscles of mastication (temporalis, masseter, and pterygoids)
- anterior digastric
- mylohyoid
- tensor tympani
- anterior 2/3 of the tongue
cranial nerve associated with 1st arch
trigeminal nerve (CN V), specifically the maxillary and mandibular divisions
1st pharyngeal arch artery gives rise to
a portion of the maxillary artery
2nd pharyngeal arch forms what skeletal structures
- Reichart’s cartilage -> stapes of middle ear
- styloid process of temporal bone
- lesser cornu (horn) and upper body of hyoid bone
muscle derived from 2nd arch
- muscles of facial expression
- stapedius
- stylohyoid
- posterior belly of digastric muscle
nerve associated with 2nd arch
facial nerve (CN VII)
Artery of the 2nd arch form
- 2 embryonic arteries: stapedial and hyoid
* hyoid develops into a small branch of the internal carotid
3rd pharyngeal arch forms
greater cornu and lower body of hyoid bone
muscles derived from 3rd arch
stylopharyngeus muscle
nerve associated with 3rd arch
glossopharyngeal nerve (CN IX)
artery of the 3rd arch
common carotid and proximal part of the internal carotid on each side
4th and 6th pharyngeal arches form
they fuse to form laryngeal cartilages: •thyroid •cricoid •aryntenoid •corniculate •cuneiform
muscle derived from 4th and 6th arches
laryngeal muscles
4th arch also forms (muscles)
cricothyroid, levator palatini, and pharyngeal constrictors
6th arch also forms (muscles)
intrinsic muscles of the larynx (except cricothyroid)
4th arch artery
arch of aorta on left and proximal part of Right subclavian on the right
6th arch artery
- proximal left pulmonary artery and ductus arteriosus on the left
- right pulmonary artery on the right
nerve associated with 4th and 6th arch
vagus (CN X)
key to remember for 1st arch
- nerve= trigeminal (V)
* structure= maxilla/mandible
key to remember for 2nd arch
- nerve= facial (VII)
* structure= hyoid
key to remember for 3rd arch
- nerve= glossopharyngeal (IX)
* structure= hyoid
key to remember for 4th and 6th arches
- nerve= vagus (X)
* structure= larynx
specific part of nerve associated with 4th arch
superior laryngeal branch of vagus
specific part of nerve associated with 6th arch
recurrent laryngeal branch of vagus
ligaments derived from 1st arch
- anterior ligament of malleus
* sphenomandibular ligament
ligament derived from 2nd arch
stylohyoid ligament
1st pharyngeal cleft develops
- external auditory meatus
* external part of tympanic membrane
1st pharyngeal pouch develops
- internal part of tympanic membrane
- tympanic cavity (middle ear)
- auditory (Eustachian) tube
2nd pharyngeal pouch develops
palatine tonsil
3rd pharyngeal pouch develops
- inferior parathyroid glands
* thymus
4th pharyngeal pouch develops
- superior parathyroid
* ultimobranchial body -> parafollicular cells (C cells) of thyroid
cervical sinus
a temporary structure formed when 2nd arch grows over and fuses with the 3rd and 4th arches, previously the 2nd-4th pharyngeal clefts
abnormal fusion of the 2nd, 3rd and 4th arches can cause
- cervical or branchial fistula
- cervical cyst
- branchial cleft cyst
cervical cyst or branchia cleft cyst
- present as neck mass
- always lateral, anterior to sternocleidomastoid muscle, below angle of mandible, immobile, and may occur on 1 0r both sides
tongue mucosa develops
from the floor endoderm lining pharyngeal arches. Innervation of tongue correlates with its developmental origin
thyroid gland develops from
midline endoderm of floor of pharynx, grows inferiorly into the neck
thyroglossal duct
connects the developing thyroid to the pharynx, and breaks down
foramen cecum
the former site of thyroglossal duct in adults
pyramidal lobe of thyroid
remnamts of thyroglossal duct can remain in adults
midline thyroid tissue or thyroglossal cysts
can be found anywhere along the path of thyroid descent
thyroglossal duct cysts present as
midline neck mass, usually painless and mobile.
most common place to find ectopic thyroid tissue
base of tongue
as thyroid gland descends…
superior and inferior parathyroid glands and parafollicular cells embed themselves in its posterior surface
face develops from
frontonasal prominence and 1st pharyngeal arch (maxillary and mandibular prominences)
prominence also =
process
2 depressions on frontonasal process
form nasal pits and create ridges of tissue called medial and lateral nasal processes
intermaxillary process
- formed when maxillary processes grow and cause medial nasal processes to fuse in midline
- becomes the bridge of the nose and philtrum of upper lip
maxillary and medial nasal processes fuse to form
the rest of the upper lip and the primary palate
maxillary and lateral nasal processes fuse to form
cheeks and alae (wings) of nose
mandibular processes fuse
in the midline to form lower lip and jaw
secondary palate forms from
fusion betwen 2 ridges of tissue (palatal shelves) growing from the oral surfaces of the maxillary process
incisive foramen marks
- the junction between primary and secondary palate
* vessels and nerves pass through it
cleft lip results from
- incomplete or lack of fusion of the maxillary process with the medial nasal processes
- can be unilateral or bilateral
- cleft lip and palate can be isolated or occur together
cleft palate resuls from
- incomplete or lack of fusion of palatal shelves
* cleft lip and palate can be isolated or occur together
eye derives from
- neuroectoderm (otic cup)
* ectoderm (lens)
optic vesicles develop as
lateral outpocketings of the neural tube, deep to the surface ectoderm
optic vesicle invaginates to form ___ and causes
optic cup, which causes overlying ectodem to form lens placode
what is a placode
thickening of ectoderm
lens placode becomes
lens vesicle and then the lens
optic cup develops into
neural retina and pigmented epithelium of retina
ventral part of optic stalk also invaginates…
and optic cup folds around the invagination to form choroidal or optic fissure
what passes through optic fissue
hyaloid artery branches from the ophthalmic artery (of the internal carotid) and enters the optic cup through optic fissure
hyaloid artery and vein become
central artery and vein of the retina
optic nerve is formed
in development of neural retina, axons of ganglion cells move along surface of retina and through the optic stalk to the brain to from optic nerve
anterior rim of optic cup develops into
iris
mesenchyme surround the optic cup forms what parts of the eye
choroid, sclera, cornea, and extraocular muscles
choroid
•layer of blood vessels and CT between sclera and retina
sclera
- the white outer wall of eye
- tough, fibrous tissue
- extends from cornea to the optic nerve at the back of the eye
choroid is a continuation of
pia mater
sclera is a continuation of
dura mater
cornea
the clear front section of the eye
eyelids develop as
- ectodermal folds with a mesenchymal core (from 1st pharyngeal arch)
- they grow toward each other in front of cornea and fuse by 8 weeks before reopening between 5th and 7th months
coloboma
•results when optic fissure fails to fuse, leaving a gap in eye structures •complete coloboma extends through entire eye (optic nerve to iris) coloboma iridis (of the iris) more localized
congenital cataracts
(lens opacities)
can result from genetic or environmental factors
genetic factors of congenital cataracts
diverse genes ranging from structural components of lens (ie mutations in CRYSTALLIN or gap junction proteins) to transcription factors
cataracts may also develop as a result of
- metabolic disorders, such as galactosemia (defect in galactose metabolism)
- congenital infections such as rubella
detached retina
- can be congenital or from head trauma
* neural retina detaches from pigmented retina
external ear develops from
- external auditory meatus from 1st cleft
* pinna or auricle from the ectoderm and underlying mesenchyme surrounding the 1st cleft (1st and 2nd arches)
middle ear develops from
- auditory ossicles (malleus, incus, stapes) from the 1st and 2 arches
- tympanic cavity and auditory tube from 1st pharyngeal pouch
inner ear develops from
•cochlea and vestibular apparatus (3 semicircular canals, utricle, saccule) from the ectoderm of the otic placode
auricle develops from
6 auricular hillocks (proliferating ectoderm underlying mesenchyme) on the 1st and 2nd arches during the 5th week
external auditory meatus develops from
1st pharyngeal cleft
structural abnormalities of external ear lead to
conductive hearing loss, as they impeded conduction of sound to the inner ear
defects of the pinna and auricle result from
abnormal growth of 1 or more of the auricular hillocks
suppressed growth of all hillocks results in
microtia (small auricle) or anotia (absence of auricle)
overgrowth of hillocks results in
macrotia (large auricle)
accessory hillocks produce
preauricular tags, which may or may not be accompanied by preauricular pits
defects of external auditory meatus include
atresia and stenosis
microtia occurs in several single-gene disorders..
- branchio-oto-renal (BOR)
- CHARGE
- Treacher collins syndromes
- trisomy 21 and 18
mocrotia can occur following prenatal exposure to
alcohol or isotretinoin
macrotia can occur in
fragile x syndrome, the most common cause of mental retardation in males
microtia and preauricular tags occur in
oculoauriculo-vertebral spectrum (OAVS)
auditory ossicles condense in
1st and 2nd pharyngeal arch mesenchyme
1st pharyngeal pouch becomes
auditory tube and tympanic cavity
tympanic cavity encloses
auditory ossicles
eardrum (TM) is derived from
opposed ectoderm and endoderm of the 1st pharyngeal cleft and pouch, called the 1st pharyngeal membrane
meatal plus
- formed by proliferating ectodermal cells of the cleft
* later thins out to establish eardrum
defects of the middle ear
- also cause conductive hearing loss
- can result from abnormal formation of the malleus, incus, and stapes, derived from neural crest cells of 1st and 2nd arches
middle ear defects occur in association with
- skeletal dysplasias, such as achondroplasia (FGFR3 mutation) and osteogenesis imperfects
- or in various syndromes such as BOR, treacher collins, or OAVS
inner ear develops from
ectodermal otic placode, which invaginates and then pinches off to form otic vesicle
otic placode also gives rise to
sensory ganglia of vestibulocochlear nerve
otic vesicle forms
endolymphatic duct, pars superior, and pars inferior
pars superior froms
3 semicircular canals and utricle
pars inferior forms
cochlear duct and saccule
membranous labyrinth
constituted by all the otic vesicle derivatives: endolymphatic duct, pars superior, and pars inferior
sensorineural hearing loss
can arise from defects of inner ear, vestibulocochlear nerve, or auditory regions of the brain
about half of hearing loss
- has genetic causes
- other half - environmental, including in utero viral infections and neonatal exposure to aminoglycoside abx
- postnatal exposure to loud noise can also cause hearing loss
