test 2 Lecture 17 sense organs Flashcards by jillian Bastidas

___ form sensory neurons

cranial placodes

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what are the three cranial placodes in order from top to bottom

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placode formation starts with thickening of the ___ then __

ectoderm

invagination

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what is different between the lens vesicle and the otic vesicle and olfactory vesicle

the lens vesicle does not produce sensory neurons

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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

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The otic placode gives rise to the sensory epithelium of the ear and to neurons that help form the ___.

cochlear-vestibular ganglion

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Trigeminal placodes

sensory neurons that innervate the face and jaw

ophthalmic and maxillomandibular

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epibranchial placodes

Nodose: forms sensory neurons innervating heart, lungs, gut

Petrosal & geniculate placodes: forms neurons innervating taste buds

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eye development involves ectoderm, ___, and mesenchyme

neural crest cells

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eye development starts with ___

outpocketing of the wall of the diencephalon

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___: inducer tissue & the responding tissue

Inductive interactions

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head mesenchyme produce ___ which will stimulate the formation of ___ in the eye

TGF-beta

retinal pigmented epithelium (RPE)

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In the eye, ___ produced by the presumptive lens placode will inhibit the production of RPE and form ___

FGF

neural retina (NR)

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Factors secreted by the presumptive lens placode (FGFs) promote ___

neural retina (NR).

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Factors produced by the head mesenchyme surrounding the optic vesicle (TGFbeta) directs ___ formation.

retinal pigmented epithelium (RPE)

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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.

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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

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Cells in the ___ absorb excess light and transport oxygen and nutrients to photoreceptors.

RPE (melanocytes)

retinal pigmented epithelium (RPE)

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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

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Blood vessels gain access to the eye through the ___

optic stalk.

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2 layers of the optic cup

thick inner layer:

neural retina (NR)

thin outer layer:

retinal pigmented epithelium (RPE)

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___ a sensory layer that receives visual images, converts into signals transmitted through optic nerve

neural retina (NR),

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optic stalk becomes the ___

optic nerve

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lens specification depends on optic ___

vesicle

Ablation of the optic vesicle prevents the formation of the lens.

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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)