sievert H&N development Flashcards
Three main types of primodia
placodes
somites
pharyngeal/branchial arches (branchial = pharyngeal… they’re synonyms)
location of branchial cleft and branchial pouch, respectively
Cleft on outside
Pouch on inside
both of these are invaginations in the inferior portion of pharyngeal/branchial arches
define a placode
ECTOdermal thickening (of the neural tube) that eventually only allows for the development of the ear or lens or olfaction
list the three placodes
olfactory (in forebrain)
lens (in outpouching of forebrain)
otic (around hindbrain)
What makes a somite preotic or postotic?
relative to the location of the otic placode.
preotic (upper to otic placode)
postotic (lower to otic placode)
where does the olfactory epithelium come form, and what does it do?
- comes from the nasal/olfactory placode
- fxn: comprises the true organs of smell, the ones w/all the receptors in the olfactory epithelium in the high superior border of nasal cavity.
etiology and fate of nasal/olfactory placode
- Forebrain (telencephalon) has a bulge, this structure is called the olfactory bulb
- This olfactory bulb induces the olfactory placode to start thickening.
- The placode makes the primary olfactory epithelium.
- Primary olfactory epithelium will end up growing up into the olfactory bulb
- How? By have to penetrating through the cribriform plate of the ethmoid bone
how is the lens placode different than the other two placodes?
the other two make the sensory bodies of the nervous system BUT lens placode has NOTHING to do w/receptors… it only makes the lens
how are lens made?
- First of all, an outpocketing of the diencephalic midbrain INDUCES the surface ectoderm to thicken, forming the lens placode
- Lens placode thickens and invaginates and breaks off to make the lens.
- The remaining part of the surface ectoderm, the part that didn’t beak off, becomes the cornea
how does the retina form?
the retina forms by an outpocketing of the diencephalon, and as the retina develops, it will be covering over the lens (basically lens placode invaginates into the developing retina)
what does the otic placode make, and how?
inner ear—membranous labyrinth, sensory neurons, and ganglion cells of CN 8
Otic placode is induced by the nervous system, specifically the hindbrain; the surface ectoderm ends up invaginating, forms otic vesicle, and then forms the future innr ear
how is the future middle ear made?
the endodermal lining of the pharynx (as part of the 1st branchial/pharyngeal pouch) makes a bilateral outpouch–this outpouch becomes the future middle ear cavity
how does the future external canal get made?
an additional invagination of surface ectoderm (branchial/pharyngeal groove)—not part of placode but is associated w/ cleft
from what does the tympanic membrane form?
mesenchyme situated between the middle and inner ear will eventually make the t-membrane
why is ear so susceptible to environmental effects?
coz it takes so long to develop and a long time to pick up said effects
How are CN ganglia similar to DRG?
- no synapse
- pseudounipolar cells w/ peripheral and central processes
define somites
masses of mesoderm that form skeletal muscles
preotic somites define. include CN too
Preotic somites form muscles that move the eye (+levator palpebrae), not the muscles of the iris or the lens (innervated by CN 3 4 and 6, respectively )
postotic somites define. include CN too
Postotic somites form muscles of the tongue, CN 12
how do you classify muscles that came from somites?
general somatic efferents
how do you classify muscles that have fibers related to visceral structures, SM or cardiac?
general visceral efferents
define branchiomotor
muscles that came from branchial/pharyngeal arch mesenchyme… functionally the same as skeletal
define pharyngeal arch. when do they appear
Masses of mesenchyme tissue that flank the developing gut tube
appear around the 4th-5th week
describe the structure of each arch
outer half covering = ectoderm
inner half covering = endoderm
core region = mesenchyme
suspended within that mesenchyme, laterally we have a nerve, cartilage/bone in the middle, and an artery more medially.
describe the arch numbering
we have six arches present, two go away or merge.
arches 1-4
arch 5 gets overridden
arch 4 and 6 merge together
location of laryngeal orifice
right under the fourth arch
what role do neural crest ells play in the arches?
they migrate into these arches, forming their nerve component
fxn: to contribute to the skeletal components of face
list the four pharyngeal arch derivatives
- muscle (probably from the -mesenchyme)
- bone/cartilage (from the bone/cartilage component of arch)
- skin (from the ectoderm of arch)
- gut tube (from endoderm)
what formed the upper and lower jaws (maxilla and mandible, respectively?
what is the name for the ear upper jaw element and the early lower jaw element?
cartilage/bone of the first pharyngeal/branchial arch
maxillary process
mandibular process
skeletal elements:
maxillary process forms the
maxilla
zygomatic bone
part of temporal bone
skeletal elements:
mandibular process forms the
mandible
malleus
incus
Skeletal elements:
second arch is also known as?
hyoid arch
skeletal elements:
second/hyoid arch forms?
lesser horn of hyoid bone
styloid process
stapes
skeletal elements:
origins of the ear bones
malleus + incus from first arch (mandibular process)
stapes from second arch
skeletal elements:
what does the third arch make?
rest of hyoid bone
remember that lesser horn of hyoid formed by the second/hyoid arch
skeletal elements:
what do the fourth and sixth arches form?
4th and 6th fuse. then they make the laryngeal cartilages
pharyngeal arch muscles:
first arch?
muscles of mastication!!!! these are the only ones innervated by first arch
pharyngeal arch muscles:
2nd arch?
muscles of fascial expression
pharyngeal arch muscles:
third arch?
just the stylopharyngeus.
goes from styloid process to the pharynx
pharyngeal arch muscles:
4th+6th arches?
muscles of palate, pharynx, and larynx
when it comes to sensory innervation (maybe motor too, but i’m not sure yet), the nerves of EACH respective arch innervate what?
the endodermal lining of each respective arch
what happens to the endodermal lining of the second arch?
its sensory lining gets overgrown by the first arch
describe the sensory innervation of the tongue?
anterior 2/3rds: lined by ectoderm, first arch zone
posterior third: lined by endoderm (allegedly, waiting of sievert’s response), THIRD arch zone. is behind the sulcus terminalis.
foramen cecum
see what sievert says!
describe etiology of sensory innervation of the epiglottis
comes form fourth arch?
what CN does the first arch and the cutaneous innervation of the anterior tongue?
5th cranial nerve
what does the first pharyngeal cleft make?
external auditory meatus
what do clefts 2 3 and 4 make?
they close ff tho make cervical sinuses/cysts, but you usually don’t see anything associated w/ it
first pouch does what?
develops into auditory and primitive middle ear cavity
second pouch develops what?
palatine tonsils
third pouch develops to what?
thymus and inferior parathyroid glands
talk about the migration of the thymus and its relationship to the parathyroid glands?
During dev, the thymus migrates from the back of the tongue, into the the foramen cecum area, down into the chest. As it does so, it pulls the inferior thyroid gland down with it until it’s below the superior. That’s why the superior pouch (third) gives rise for the inferior PT gland.
this is is weird coz embryologically, the inferior PT gland, thymus (inf PT connected to thymus), and superior PT gland
fourth pouch gives rise to?
superior PT gland
fifth pouch gives rise to?
parafollicular C cells
CN 5 does what?
motor to muscles of mastication, but it’s main fxn is sensory
list the cranial nerves to placodes
1, 2, and 8
list cranial nerves to somites
3, 4, 6 (preotic, only somatomotor, extraocular eye muscles)
and
12 (postotic, only somatomotor, hypoglossal to tongue)
list cranial nerve to branchial branches
V
VII
IX
and X
CN 1:
full name
primoridium
olfactory n
olfactory placode
CN 2:
full name
primoridium
optic nerve
optic vesicle
CN 3:
full name
primoridium
oculomotor
preotic somite
CN 4:
full name
primoridium
trochlear
preotic somite
CN 5:
full name
primoridium
trigeminal
branchial arch 1
CN 6:
full name
primoridium
abducens preotic somite (3 4 and 6 all extraocular eye)
CN 7:
full name
primoridium
fascial
branchial arch 2
CN 8:
full name
primoridium
vestibulocochlear
otic placode
CN 9:
full name
primoridium
glossopharyngeal
branchial arch 3
CN 10:
full name
primoridium
vagus
branchial arch 4, also branchial arch 6
CN 11:
full name
primoridium
spinal accessory
probably branchial but dunno for sure
CN 12:
full name
primoridium
hypoglossal
postotic somite
