Week 3 - Neuro Embryology Flashcards
primordia of head, neck, face, palate, nasal cavity
present by 4-5 wks
pharyngeal apparatus
arches, clefts, pouches, membranes - surrounds foregut, is source of mesenchyme that forms the head, neck, face, palate, nasal cavity
facial prominences
frontonasal, maxillary, mandibular
combine to form 1st pharyngeal arch
maxillary and mandibular prominence
frontonasal prominence
single anterior bulge where forebrain is developing, cranial neural tube overgrows the pharynx
pharyngeal arches
bulges 1-6 (no 5) - 5 pairs, bars of mesenchyme covered with ectoderm externally and endoderm internally, form around foregut, formed by folding of lateral plate mesoderm, have associated aortic arch, somite/somitomere mesoderm and neural crest cells and nerves migrate into arches
pharyngeal clefts
indents between pharyngeal arches, four pairs 1-4, ectoderm external surface
pharyngeal pouches
indents inside the gut tube, opposite pharyngeal clefts, pairs 1-4, endoderm internal surface
pharyngeal membrane
thin area of tissue that between pharyngeal clefts and pharyngeal pouches as development progresses, ectoderm externally, endoderm internally, mesenchyme between, membranes do not break down in humans but they do break down in fish
maxillary prominence
part of 1st pharyngeal arch
mandibular prominence
part of 1st pharyngeal arch - fuse during week 4 to form lower lip/jaw/face
oropharyngeal membrane
membrane that covers hole between maxillary and mandibular prominences where mouth would be
somites / somitomeres
mesoderm migrates from them into pharyngeal arches, becomes most muscles of the face and parts of the skulls, ex: eye muscles from somitomeres and tongue from occipital somites
neural crest cells
migrate into pharyngeal arches, form skeletal parts of the head and PNS ganglia in the head
elements in each pharyngeal arch
skeletal (bones, cartilage, ligaments of head), muscular (skeletal muscles of head), neural (cranial nerves), vascular (aortic arch arteries)
cranial nerve
neurons from brain and cranial ganglia grown into specific pharyngeal arches forming cranial nerves - each arch has a single cranial nerve
1st arch muscles
trigeminal nerve, V3 to muscles of mastication
2nd arch muscles
facial nerve to muscles of facial expression
3rd arch muscles
glossopharyngeal nerve to stylopharyngeus
4th arch muscles
vagus nerve to pharyngeal constrictors
6th arch muscles
vagus nerve to laryngeal muscles
1st pharyngeal arch
maxillary prominence becomes upper jaw (maxilla/zygomatic/squamous temporal bone - intermembranous), mandibular prominence becomes lower jaw, Meckel’s cartilage is replaced by mandible/malleus/incus/spine of sphenoid, muscles - temporalis/masseter/mylohyoid/ant belly digastric/tensor tympani/tensor veli palatini, nerve - trigeminal V3
2nd pharyngeal arch
Reichert’s cartilage is replaced by stapes/styloid process/stylohyoid ligament/lesser cornu of hyoid, muscles - facial expression/post belly digastric/stylohyoid/stapedius, bones of endochondral ossification
3rd pharyngeal arch
greater cornu of hyoid bone, glossopharyngeal nerve to stylopharyngeus
4th pharyngeal arch
thyroid and cricoid cartilage, nerve - superior laryngeal of vagus nerve, muscles - soft palate (except tensor veli palatini), pharynx, cricothyroid, cricopharyngeus, sensation about vocal cords
6th pharyngeal arch
thyroid and cricoid cartilage, nerve - recurrent laryngeal of vagus, intrinsic muscles of larynx (except cricothyroid), striated upper muscles of esophagus
all nerves of pharyngeal arches
are special visceral efferents
first pharyngeal pouch endothelial cells
auditory tube (epi lining), middle ear (epi lining), mastoid air cells
second pharyngeal pouch endothelial cells
palatine tonsils (epi component, no lymphatic)
third pharyngeal pouch endothelial cells
thymus, inferior parathyroid glands
fourth pharyngeal pouch endothelial cells
superior parathyroid glands, ultimobrachial bodies (thyroid)
thymus
from 3rd pharyngeal arch, migrates down behind sternum, capsule from neural crest cells, populated by thymocytes from hematopoetic stem cells, involutes in adolescence, still functional in adults
1st pharyngeal cleft
external auditory meatus (epi lining)
2nd, 3rd, 4th pharyngeal clefts
normally grown over by 2nd pharyngeal arch, leaving smooth surface and no gill slits - can create cervical sinus when covered which can lead to cervical cysts or fistulas
1st pharyngeal membrane
becomes tympanic membrane with three layers - ectoderm, mesosderm, endoderm
thyroid gland
forms from evagination of floor of pharynx between 1st and 2nd arches, remains connected to tongue via foramen cecum and thyroglossal duct, small piece of superior thyroid tissue called pyramidal lobe in 50% of pts, follicular cells from thyroid diverticulum and parafollicular cells from 4th pharyngeal pouch come together to form thyroid gland
tongue development
from floor of pharynx, involves arches 1-4, ant 2/3 = oral, post 1/3 = pharyngeal
ant 2/3 tongue (oral)
from 1st arch mesenchyme, distal tongue buds overgrow the median tongue bud and leave a median sulcus in the tongue
post 1/3 tongue (pharyngeal)
from 3rd arch mesenchyme, 3rd arch hypobrachial eminence overgrows the 2nd arch copula so the 2nd arch does not contribute to the tongue
terminal sulcus
boundary between 2/3 ant and 1/3 post tongue, where buccopharyngeal membrane used to be
epiglottis and extreme posterior tongue
from 4th arch mesenchyme
tongue muscles
from myoblasts that migrate from occipital myotomes with hypoglassal nerve that ends up innervating them
motor innervation of the tongue
all muscles but palatoglossus (vagus) supplied by hypoglossal nerve CN XII
sensory innervation of the tongue
ant 2/3 - lingual nerve V3 sensory and chorda tympani CN VII with lingual taste from 1st arch, post 1/3 - glossopharyngeal nerve CN IX taste and sensory from 3rd arch, extreme posterior tongue - internal laryngeal nerve CN X vagus from 4th arch
pituitary gland
evagination upward from roof of pharynx (endoderm) becomes gland and evegination downward from hypothalamus becomes infundibulum/neurohypophysis
general somatic efferent GSE
motor to skeletal muscles
general visceral efferent GVE
motor to heart, smooth muscle, glands, parasympathetic in cranial nerves
special visceral efferents SVE
motor to skeletal muscles that develop in pharyngeal arches (pharynx, larynx, middle ear)
general somatic afferents GSA
sensation of touch, pain, temp
special somatic afferents SSA
special sense organs from ectoderm in embryo (vision, hearing)
general visceral afferents GVA
sensory from organs (heart, intestines)
special visceral afferents SVA
special sense organs developing in assciation with gut tract (smell and taste)
ear embryology
1st branchial cleft, 1st branchial pouch, otic placodes, 1st and 2nd arch derivatives
nasal cavity embryology
nasal placodes form nasal pits in ectoderm, nasal sacs deepen from mesenchyme proliferation of medial and lateral nasal prominences, temporary epi plug, ***nasobuccal membrane ruptures
palate embryology
5-12th wks, 6-9th wks key, primary palate - medial nasal prominences fuse ant to incisive foramen, secondary palate - lateral palatine prominences form medial maxillary prominences (allowed when tongue drops with mandibular formation) fuses with septum and primary palate, ossification in ant-post direction
thyroid embryology
4th wk endoderm foregut thickening, thyroid diverticulum forms, thyroid descends ant to hyoid and thyroid cartilage, 7th wk thyroid reaches location and thyroglossal duct degenerates
placodes
thickening of ectoderm - nasal placodes, lens placodes, otic (inner ear) placodes
stomodeum and oropharyngeal (buccopharyngeal) membrane
found in the space where the mouth will be, stomodeum from ectoderm of oropharyngeal membrane, is at level of terminal sulcus of tongue, breaks down
rostral 1st pharyngeal arch
covered with ectoderm on both sides up to buccopharyngeal membrane, represents transition from keratinized to non-keratinized mucosa to gut tube endoderm
nasal placodes
rostral frontonasal prominence, medial and lateral nasal prominences around each placode, form nose and upper lip, develop during 5th wk, medial nasal placode migrate toward each other and fuse
mandible
formed from the fusion of the mandibular prominences (1st arch) during wk 4 and endochondral ossification
medial nasal prominences (in frontonasal prominence)
medial side of nasal placodes, migrate toward each other and fuse during wk 6-7 forming intermaxillary segment that gives rise to nasal septum, philtrum, pre-maxilla, and primary palate
maxillary prominence (1st pharyngeal arch)
grows medially, fusing with medial nasal prominences/lateral nasal prominences/mandibular prominences, forms cheek, lateral upper lip, secondary palate
palate development
critical wks 6-9, primary palate - from intermaxillary segment of fused medial nasal prominences of frontonasal prominence, secondary palate - from palatine shelves of maxillary prominence of 1st pharyngeal arch ossifies ant - post
incisive canal
where primary and secondary palate development meet and fuse, entire thing is called the definitive palate
hard palate
ossified primary palate and ant secondary palate
soft palate
unossified post secondary palate and uvula
nasal septum
formed from fused medial nasal prominences grows down and fuses with definitive palate - gives rise to perp plate of ethmoid and vomer
nostrils/nasal cavities
medial/lateral nasal prominences enlarge with proliferation of mesenchyme, nasal pits deepen created blind primitive nasal cavities which become connected to the oral cavity when the oronasal membrane ruptures making primitive choanae, as the secondary palate forms true choanae develop, nasal conchae protrude and olfactory epi develops in roof of nasal cavity
paranasal air sinuses
formed after birth as outgrowths of walls of nasal cavity (only maxillary and ethmoid sinus are present at birth)
nasal conchae
develop as elevations in lateral nasal cavity wall
tooth development
maxilla and mandible grow along with tooth development, otoblasts from neural crest cells, trophic for bone dev in jaw
critical period for ear development
4-9 wks, can lead to low set ears and deafness
critical period for eye development
4-8wks, can lead to microphthalmia, cataracts, gluacoma
eye 4wks
optic vesicle forms behind lens placode, optic vesicle is in the prosencephalon/diencephalon lined with neuroectoderm
neuroectoderm and eye
forms invagination called optic groove -> optic vesicle -> optic cup on optic stalk (behind lens placode), develops into retina/iris/ciliary bodies and induces surface ectoderm to become lens
lens placode
in front of optic cup of neuroectoderm, forms lens pit -> lens vesicle inside optic cup, branches of ophthalmic artery called hyaloid artery supply optic cup (retina) and lens vesicle (posterior lens)
hyaloid artery
from ophthalmic artery to optic cup and posterior lens placode usually regresses from lens by 8 months (leaving an avascular lens), occasionally it can persist in adults and interfere with vision, becomes central artery that supplies the inner layer of the optic cup
closure of optic fissure
where optic stalk wrapped around, hyaloid artery runs in it, it closes leaving a circular end opening behind lens and that becomes pupil
optic cup
from neuroectoderm, has outer and inner layer with intraretinal space between them
outer layer optic cup
becomes retinal pigmented epithelium, has strong inductive influence on neural retina, choroid, and sclera
inner layer optic cup
from neuroectoderm, becomes neural retina, supplied by hyaloid artery that becomes central artery
ciliary body
develop from inner (becomes non-pigemented ciliary layer) and outer (becomes pigmented ciliary layer) layers of optic cup anterior to the ora serrata
iris
posterior iris is a continuation of the inner and outer layers of the retinal cup, anterior iris is stromal layer with dilator and sphincter muscles and an ant layer of chromataphores / melanocytes with genetically determined density, iris arise from both ectoderm and mesoderm
sphincter and dilator pupillae
develop from neuroectoderm, unlike rule that muscles come from mesoderm
lens
optic vesicle induces lens placode to form -> lens pit -> lens vesicle -> ant and post layers of lens vesicle come together closing lumen -> lens
aqueous chambers and humor
anterior chamber is space within mesenchyme between lens and cornea, posterior chamber is a space in mesenchyme between iris and lens, both fill with aqueous humor from ciliary processes
vitreous body
from mesenchyme between lens and retina
choroid and sclear
from mesenchyme around eye induced by the retinal pigmented epithelium, choroid is inner vascular and pigements, sclera is outer tough
cornea and conjunctiva
lens induces surface ectoderm to form outer epithelium, middle stroma comes from mesenchyme, inner endothelium comes from neural crest cells migrating from optic cup
eyelids
folds of surface ectoderm and mesenchyme overgrow the eye forming eyelids
skeletal muscles and nerves of the eyelids
orbicularis oculi (2nd arch, facial nerve, SVE), levator palpebrae superioris (preo-otic myotomes, oculomotor nerve, GSE)
smooth muscle and nerve of the eyelids
superior tarsal (mesenchyme, sympathetic, GVE)
external ear
1st pharyngeal cleft and mesenchyme of 1st and 2nd phyarngeal arches
middle ear
1st pharyngeal pouch; ossicles from 1st and 2nd pharyngeal arches
inner ear
otic vesicle
otic placodes
on rhombencephalon (hindbrain), come from surface ectoderm thickening, otic placode -> otic pit -> otic vesicles (otocytes) -> membranous labyrinth
otic vesicle
becomes membranous labyrinth, induces mesenchyme to become bony labyrinth and contributes to peripheral CN VIII ganglion (statoacoustic ganglion)
dorsal (utricular) otic vesicle
becomes semicircular ducts, utricle, endolymphatic duct
ventral (saccular) otic vesicle
becomes saccule, cochlear duct, ductus reuniens
semicircular ducts
from dorsal part of otic vesicle, flat plates from utricle, fills with endolymph, ampulla and crista ampullaris form
utricle
from dorsal otic vesicle, what remains after semicircular canals form, macula utriculi form
statoacoustic ganglion
from wall of optic vesicle and neural crest cells, splits into spiral and vestibular ganglia
vestibular ganglion
bipolar 1st order afferent, from optic placode and neural crest cells, part of CN VIII - special somatic afferent
cochlear duct
from ventral otic vesicle, out of saccule, ductus reuniens remains connecting them
orga of Corti (spiral organ)
from wall of cochlear duct, hair cells innervated by bipolar cells from statoacoustic ganglion, auditory to CN VIII - special somatic afferent
otic capsule
mesenchyme surrounding otic vesicle induced to condense, outer part ossifies becoming bony labyrinth
scala vestibuli / scala tympani perilymphatic spaces
formed from vacuolization of cartilage of inner otic capsule
membranous cochlear duct
from otic vesicle, inside vacuolized cartilaginous otic capsule, composed of vestibular and basilar membranes and spiral ligament
vestibular membrane
between scala vestibuli and cochlear duct
basilar membrane
between scala tympani and cochlear duct
spiral ligament
attachment between cochlear duct and cartilage capsule
middle ear
tympanic cavity and auditory tubes form from first pharyngeal pouch, pouch grows outward and upward to surround ossicles
malleus and incus
forms from Meckel’s cartilage of 1st pharyngeal arch
stapes
forms from Reichert’s cartilage of the 2nd pharyngeal arch
mastoid air cells
from extending tympanic cavity reaching back into mastoid bone
tensor tympani
from 1st arch, from bony / cartilage auditory tube, attaches manubrium to malleus, nerve - V3 (special visceral efferent)
stapedius
from 2nd arch, from wall of tympanic cavity, attaches to stapes, nerve - facial nerve (special visceral efferent)
external ear
from 1st pharyngeal cleft, exends inward making external acoustic meatus and meatal plug (epithelial cells - later dissolves)
tympanic membrane
forms where 1st pharyngeal cleft and 1st pharyngeal groove meet, outer ectoderm layer, middle mesoderm layer, inner endodermal layer - most nociceptive receptors, overlapping innervation from facial / glossopharyngeal / vagus / trigeminal
auricle (pinna)
6 hillocks, dorsal half from 1st arch and half from 2nd arch, fuse into folds around 1st cleft and move upward and backward as mandible lengthens
1st hillock
from 1st arch, gives rise to tragus, crus of helix, and helix - sensory from CN V
2nd hillock
from 2nd arch, gives rise to antihelix, antitragus, and lobule - sensory cervical plexus and facial nerve
dermatomes of neck
surface ectoderm of 2nd - 6th arches go into cervical sinus and disappear that is why spinal nerve innervation starts below V3
