sievert H&N development

Question 1

Three main types of primodia

Answer 1

placodes
somites
pharyngeal/branchial arches (branchial = pharyngeal… they’re synonyms)

Question 2

location of branchial cleft and branchial pouch, respectively

Answer 2

Cleft on outside
Pouch on inside

both of these are invaginations in the inferior portion of pharyngeal/branchial arches

Question 3

define a placode

Answer 3

ECTOdermal thickening (of the neural tube) that eventually only allows for the development of the ear or lens or olfaction

Question 4

list the three placodes

Answer 4

olfactory (in forebrain)
lens (in outpouching of forebrain)
otic (around hindbrain)

Question 5

What makes a somite preotic or postotic?

Answer 5

relative to the location of the otic placode.

preotic (upper to otic placode)
postotic (lower to otic placode)

Question 6

where does the olfactory epithelium come form, and what does it do?

Answer 6

• 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.

Question 7

etiology and fate of nasal/olfactory placode

Answer 7

• 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

Question 8

how is the lens placode different than the other two placodes?

Answer 8

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

Question 9

how are lens made?

Answer 9

• 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

Question 10

how does the retina form?

Answer 10

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)

Question 11

what does the otic placode make, and how?

Answer 11

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

Question 12

how is the future middle ear made?

Answer 12

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

Question 13

how does the future external canal get made?

Answer 13

an additional invagination of surface ectoderm (branchial/pharyngeal groove)—not part of placode but is associated w/ cleft

Question 14

from what does the tympanic membrane form?

Answer 14

mesenchyme situated between the middle and inner ear will eventually make the t-membrane

Question 15

why is ear so susceptible to environmental effects?

Answer 15

coz it takes so long to develop and a long time to pick up said effects

Question 16

How are CN ganglia similar to DRG?

Answer 16

• no synapse

- pseudounipolar cells w/ peripheral and central processes

Question 17

define somites

Answer 17

masses of mesoderm that form skeletal muscles

Question 18

preotic somites define. include CN too

Answer 18

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 )

Question 19

postotic somites define. include CN too

Answer 19

Postotic somites form muscles of the tongue, CN 12

Question 20

how do you classify muscles that came from somites?

Answer 20

general somatic efferents

Question 21

how do you classify muscles that have fibers related to visceral structures, SM or cardiac?

Answer 21

general visceral efferents

Question 22

define branchiomotor

Answer 22

muscles that came from branchial/pharyngeal arch mesenchyme… functionally the same as skeletal

Question 23

define pharyngeal arch. when do they appear

Answer 23

Masses of mesenchyme tissue that flank the developing gut tube

appear around the 4th-5th week

Question 24

describe the structure of each arch

Answer 24

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.

Question 25

describe the arch numbering

Answer 25

we have six arches present, two go away or merge. arches 1-4 arch 5 gets overridden arch 4 and 6 merge together

Question 26

location of laryngeal orifice

Answer 26

right under the fourth arch

Question 27

what role do neural crest ells play in the arches?

Answer 27

they migrate into these arches, forming their nerve component fxn: to contribute to the skeletal components of face

Question 28

list the four pharyngeal arch derivatives

Answer 28

- muscle (probably from the -mesenchyme) - bone/cartilage (from the bone/cartilage component of arch) - skin (from the ectoderm of arch) - gut tube (from endoderm)

Question 29

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?

Answer 29

cartilage/bone of the first pharyngeal/branchial arch maxillary process mandibular process

Question 30

skeletal elements: | maxillary process forms the

Answer 30

maxilla zygomatic bone part of temporal bone

Question 31

skeletal elements: | mandibular process forms the

Answer 31

mandible malleus incus

Question 32

Skeletal elements: | second arch is also known as?

Answer 32

hyoid arch

Question 33

skeletal elements: | second/hyoid arch forms?

Answer 33

lesser horn of hyoid bone styloid process stapes

Question 34

skeletal elements: | origins of the ear bones

Answer 34

malleus + incus from first arch (mandibular process) stapes from second arch

Question 35

skeletal elements: | what does the third arch make?

Answer 35

rest of hyoid bone | remember that lesser horn of hyoid formed by the second/hyoid arch

Question 36

skeletal elements: | what do the fourth and sixth arches form?

Answer 36

4th and 6th fuse. then they make the laryngeal cartilages

Question 37

pharyngeal arch muscles: | first arch?

Answer 37

muscles of mastication!!!! these are the only ones innervated by first arch

Question 38

pharyngeal arch muscles: | 2nd arch?

Answer 38

muscles of fascial expression

Question 39

pharyngeal arch muscles: | third arch?

Answer 39

just the stylopharyngeus. goes from styloid process to the pharynx

Question 40

pharyngeal arch muscles: | 4th+6th arches?

Answer 40

muscles of palate, pharynx, and larynx

Question 41

when it comes to sensory innervation (maybe motor too, but i'm not sure yet), the nerves of EACH respective arch innervate what?

Answer 41

the endodermal lining of each respective arch

Question 42

what happens to the endodermal lining of the second arch?

Answer 42

its sensory lining gets overgrown by the first arch

Question 43

describe the sensory innervation of the tongue?

Answer 43

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.

Question 44

foramen cecum

Answer 44

see what sievert says!

Question 45

describe etiology of sensory innervation of the epiglottis

Answer 45

comes form fourth arch?

Question 46

what CN does the first arch and the cutaneous innervation of the anterior tongue?

Answer 46

5th cranial nerve

Question 47

what does the first pharyngeal cleft make?

Answer 47

external auditory meatus

Question 48

what do clefts 2 3 and 4 make?

Answer 48

they close ff tho make cervical sinuses/cysts, but you usually don't see anything associated w/ it

Question 49

first pouch does what?

Answer 49

develops into auditory and primitive middle ear cavity

Question 50

second pouch develops what?

Answer 50

palatine tonsils

Question 51

third pouch develops to what?

Answer 51

thymus and inferior parathyroid glands

Question 52

talk about the migration of the thymus and its relationship to the parathyroid glands?

Answer 52

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

Question 53

fourth pouch gives rise to?

Answer 53

superior PT gland

Question 54

fifth pouch gives rise to?

Answer 54

parafollicular C cells

Question 55

CN 5 does what?

Answer 55

motor to muscles of mastication, but it's main fxn is sensory

Question 56

list the cranial nerves to placodes

Answer 56

1, 2, and 8

Question 57

list cranial nerves to somites

Answer 57

3, 4, 6 (preotic, only somatomotor, extraocular eye muscles) and 12 (postotic, only somatomotor, hypoglossal to tongue)

Question 58

list cranial nerve to branchial branches

Answer 58

V VII IX and X

Question 59

CN 1: full name primoridium

Answer 59

olfactory n | olfactory placode

Question 60

CN 2: full name primoridium

Answer 60

optic nerve | optic vesicle

Question 61

CN 3: full name primoridium

Answer 61

oculomotor | preotic somite

Question 62

CN 4: full name primoridium

Answer 62

trochlear | preotic somite

Question 63

CN 5: full name primoridium

Answer 63

trigeminal | branchial arch 1

Question 64

CN 6: full name primoridium

Answer 64

``` abducens preotic somite (3 4 and 6 all extraocular eye) ```

Question 65

CN 7: full name primoridium

Answer 65

fascial | branchial arch 2

Question 66

CN 8: full name primoridium

Answer 66

vestibulocochlear | otic placode

Question 67

CN 9: full name primoridium

Answer 67

glossopharyngeal | branchial arch 3

Question 68

CN 10: full name primoridium

Answer 68

vagus | branchial arch 4, also branchial arch 6

Question 69

CN 11: full name primoridium

Answer 69

spinal accessory | probably branchial but dunno for sure

Question 70

CN 12: full name primoridium

Answer 70

hypoglossal | postotic somite