test 2 Lecture 17 sense organs Flashcards
___ form sensory neurons
cranial placodes
what are the three cranial placodes in order from top to bottom
placode formation starts with thickening of the ___ then __
ectoderm
invagination
what is different between the lens vesicle and the otic vesicle and olfactory vesicle
the lens vesicle does not produce sensory neurons
The olfactory placode gives rise to the sensory neurons involved in smell, and also to some migratory neurons that will travel into the brain & secrete ___ releasing hormone.
gonadotropin
The otic placode gives rise to the sensory epithelium of the ear and to neurons that help form the ___.
cochlear-vestibular ganglion
Trigeminal placodes
sensory neurons that innervate the face and jaw
ophthalmic and maxillomandibular
epibranchial placodes
Nodose: forms sensory neurons innervating heart, lungs, gut
Petrosal & geniculate placodes: forms neurons innervating taste buds
eye development involves ectoderm, ___, and mesenchyme
neural crest cells
eye development starts with ___
outpocketing of the wall of the diencephalon
___: inducer tissue & the responding tissue
Inductive interactions
head mesenchyme produce ___ which will stimulate the formation of ___ in the eye
TGF-beta
retinal pigmented epithelium (RPE)
In the eye, ___ produced by the presumptive lens placode will inhibit the production of RPE and form ___
FGF
neural retina (NR)
Factors secreted by the presumptive lens placode (FGFs) promote ___
neural retina (NR).
Factors produced by the head mesenchyme surrounding the optic vesicle (TGFbeta) directs ___ formation.
retinal pigmented epithelium (RPE)
The lens placode invaginates to become a ____ , which forms a complete circle that pinches off from the surface ectoderm to become the ___
lens pit
lens vesicle.
At the same time the lens vesicle is forming, the optic vesicle also invaginates to form a double-layered structure called the ___. So at this point we see a goblet-shaped optic cup with the lens vesicle floating in its open end.
optic cup
Cells in the ___ absorb excess light and transport oxygen and nutrients to photoreceptors.
RPE (melanocytes)
retinal pigmented epithelium (RPE)
The portion of each optic vesicle that interacts with the surface ectoderm induces an area of the ectoderm to form a thickening, the ___(a precursor of the lens).
lens placode
Blood vessels gain access to the eye through the ___
optic stalk.
2 layers of the optic cup
thick inner layer:
neural retina (NR)
thin outer layer:
retinal pigmented epithelium (RPE)
___ a sensory layer that receives visual images, converts into signals transmitted through optic nerve
neural retina (NR),
optic stalk becomes the ___
optic nerve
lens specification depends on optic ___
vesicle
Ablation of the optic vesicle prevents the formation of the lens.
lens vesicle will close, move away from the ___, and form __ inside the optic cup
ectoderm
lens
Bottom of optic cup forms epithelium of ___ and ciliary body
iris
inner layer (NR): forms ___ and ___
rods & cones
___ & ciliary body develop from neural crest cells migrating into this area
Stroma of iris
___ in stroma of the iris determines eye color
Melanin
explain how lens is formed
cell differentiation within the lens
anterior cuboidal epithelial cells
dividing epithelial cells
elongation
stops dividing and elongates more and become mature posterior fiber cells with crystallin
crystallin
90% of total lens protein are crystallins
10% insoluble albuminoids
3 types of crystallin
Alpha-crystallin:
•Largest crystallin• 31% total lens proteins
Beta-crystallin:
•Most abundant•55% heterogenous
Gamma-crystallin:
Smallest and least abundant (2%)
3 types of crystallins
Alpha-crystallin:
•Largest crystallin• 31% total lens proteins
Beta-crystallin:
•Most abundant•55% heterogenous
Gamma-crystallin:
Smallest and least abundant (2%)
beta- crystallin
Most abundant type of crystallin
55% heterogenous
alpha crystallin
- Largest crystallin
- 31% total lens proteins
gamma crystallin
Smallest and least abundant (2%)
example of reciprocal inductive interactions during eye development
optic vesicle induces the formation of lens placode which then induces formation of optic cup
___ expressed at late gastrula stage in lens ectoderm
Otx2
Inducers from neural plate initiate ___ expression in lens ectoderm, making it ___to respond to optic vesicle in late neurula stage
Pax6
competent
Optic vesicle produces BMPs that induce ___ expression at late neural stage, which initiates lens formation
Sox3
During eye development Otx2 is made after Pax6
true or false?
false
Otx2 first during mid gastrula stage
then pax6 during early neurula stage
___ competence factor that regulates eye development
Pax6
where is Pax6 found
sonic hedgehog (shh) is produced by the ___ and ___Pax6 expression in the center of the eye field.
midline tissues
suppresses
If shh signaling is impaired, Pax6 expression is sustained in the entire eye field, leading to the development of ___
one large eye
cyclopia
fusion of the eyes
synophtalmia
cyclopia is associated with underdevelopment of the forebrain and cranial defects like___ (single telenecephalic lobe).
holoprosencephaly
Factors affecting the midline structure formation of the eye include:
alcohol
abnormal cholesterol metabolism
Teratogens: cyclopamine
what causes cycolpia
Cyclopamine: teratogenic agent that inhibits the Shh signaling pathway
chemical in corn lily
NR= neural retina
RPE= retinal pigmented epithelium
three parts of the ear
outer= capture sound
middle= amplify sound
inner= transduce sound
parts of the outer ear
auricle or pinna
auditory canal - eardrum (tympanic membrane)
The outer ear is mainly formed by the cells in the ___ including arch ___ and ___.
first pharyngeal cleft,
ectoderm and mesoderm
parts of middle ear
eardrum
ossicles, three small bones
Eustachian tube: connects to the throat to equalize the pressure on both sides of the eardrum
___: connects to the throat to equalize the pressure on both sides of the eardrum
Eustachian tube
The middle ear chamber is filled with ___
air
what are the three bones of the middle ear?
malleus (hammer)
incus (anvil)
stapes (stirrup)
___ ossicles are derived from the first branchial arches.
malleus and incus
___ ossicles are derived from the 2nd branchial arch.
stapes
origin of the ossicles are ___
neural crest or paraxial mesoderm.
The cavity of the middle ear is lined by mucosal tissues of ___ origin that extends from the oral cavity.
endoderm
The first visible sign of inner ear development is the appearance of the ___, an ectodermal thickening located adjacent to rhombomeres ___ of the hindbrain.
otic placode
5 and 6
induction of otic placode
Fgf8 from endoderm
stimulates Fgf19 from mesoderm
stimulates Wnt8c and Fgf3 from neural plate
Fgf19 also prepares prospective otic placode
stimulates thickening otic placode of ectoderm
A portion of the pharyngeal endoderm sercretes Fgf8, which induces the mesoderm overlying it to secrete Fgf19.
Fgf19 is received by both the prospective otic placode and the adjacent neural plate.
Fgf19 instructs the neural plate to secrete Wnt8c and Fgf3, two paracrine factors that work synergistically to induce Pax2 and other genes that allow the cells to produce the otic placode and become sensory cells.
development of the inner ear
otic vesicle becomes
cochlear duct
semicircular canals
delaminating neuroblasts from the otic cup become
the ganglion of the 8th cranial nerve
most components of the inner ear are derived from the ___ (otic placode).
what are the exceptions?
ectoderm
Exception: the pigment cells of the stria vascularis and the secretory epithelium of the cochlea (neural crest origin); cartilaginous tissues surrounding the epithelial core of the inner ear (paraxial mesoderm).
the pigment cells of the stria vascularis and the secretory epithelium of the cochlea come from ___origin
neural crest
cartilaginous tissues surrounding the epithelial core of the inner ear come from ___ origins
paraxial mesoderm
Dorsally : semi circular canals (SCC), utricule (U) and saccule (S)
Ventrally : cochlea (C)
In its adult form, the mammalian inner ear includes six sensory patches that develop as sensory epithelia acting as the primary transducers of ___
sound, motion and gravity
Three semi-circular canals (scc) are responsible for the ___
perception and maintenance of balance
the organ of Corti, which extends along the coil of the cochlear duct, acts as the ___
primary auditory organ
the saccule (s) and utricule (u), located in the center of the inner ear,
perceives linear and angular acceleration
___ perceives linear and angular acceleration
saccule (s) and utricule (u),
___ acts as the primary auditory organ
organ of Corti
__ are responsible for the perception and maintenance of balance
Three semi-circular canals (scc)
organ of corti
- a single inner hair cell (I)
- three outer hair cells (1-3)
- a number of supporting cells
- -TC (tunnel of Corti)*
The organ of Corti is located on the floor of the ___
scala media.
___ extends dorsally to communicate with the central nervous system (CNS), allowing the passage of cerebrospinal fluid from the CNS to the inner ear, where it is called ___, an essential fluid for sensory transduction.
Endolymphatic duct
endolymph
endolymph
cerebrospinal fluid from the CNS to the inner ear,
an essential fluid for sensory transduction.
how does inner ear differ between species
utricle and semicircular canals highly conserved
auditory chamber very different:
auditory chambers in fish
The saccule and lagena are prominent auditory organs in fish but the saccule has a vestibular role in mammals and birds.
The lagena is absent in mammals and is of uncertain function in birds.
auditory chambers in birds and mammals
The primary auditory organ in birds and mammals is the cochlea (c), which has no known counterpart in fishes and amphibians.
auditory chamber in amphibian
In amphibians, the saccule is auditory, as are the basilar papilla and amphibian papilla.
what are two transcription factors for otic vesicle development
Hmx3 (semi circular canal) (top of inner ear)
Pax 2 (cochlea- bottom of inner ear)
Cochlear degeneration is the most common cause of ___ in aged animals.
acquired deafness
___ can be inherited or results from damage to the developing fetus.
Congenital deafness
___ is caused by defects in cochlear hair cells or cochlear nerve neurons.
Sensorineural deafness
merle & spotted white coats are often associated with congenital sensorineural deafness in dogs and other animals. this is because of ___
abnormal neural crest derived pigment cells
30% of dalmatians are deaf
: abnormal Sox9 expression. results in abnormal circling behavior
Vestibular apparatus dysfunction
___ are present in normal hearing tissue. They are absent or reduced when deafness occurs.
Melanocytes
Melanocytes help control the___, required for normal hearing.
endocochlear potential
what are some errors of melanocytes in association with deafness
Failure of migration of neural crest cells (melanoblasts)
Abnormal maturation of melanocytes
Premature death/dysfunction of melatocytes within cochlea (sv)
