[MOD15C - Development of Special Senses_2028]

What are the four ectodermal plates formed immediately after gastrulation?

Surface ectoderm, neuroectoderm, neural crest, ectodermal placodes

Which ectodermal plate becomes the epidermis of human skin?

Surface ectoderm

What is the role of the neural crest cells in eye development?

They differentiate into melanocytes and contribute to the iris and retinal pigment epithelium.

Which placode is responsible for the formation of the human lens?

Optic (lens) placode

At what day of development do lens placodes begin to appear?

Day 22 of age of gestation (AOG)

What structure forms from the optic stalk?

Cranial Nerve II (Optic nerve)

What is the choroid fissure and where is it located?

A temporary cleft in the inferior aspect of the eye primordium

Failure of the choroid fissure to close leads to which congenital defect?

Coloboma iridis

Which gene is the master gene for gastrulation activated at day 18?

HNF-3b

Which gene handles the further maturation of the primordial lens?

Paired Homeobox 6 (PAX-6) gene

What are the two segments of the optic cup?

Anterior segment (pars ceca retinae) and posterior segment (pars optica retinae)

Which layers of the retina are formed by the optic cup?

Outer pigment layer and inner neural layer

What do the mesodermal cells surrounding the optic cup differentiate into?

Sclera and choroid

Which extraocular muscles arise from somitomeres 1, 2, and 3?

Inferior oblique, medial rectus, inferior rectus, superior rectus, and superior oblique

The pharyngeal system is composed of five pharyngeal arches, four clefts, and four pouches.

TRUE

The tympanic membrane is derived solely from the ectoderm of the pharyngeal cleft.

FALSE

The mastoid air cells form as a result of pneumatization from the middle ear cavity.

TRUE

The lateral part of the tubotympanic recess forms the Eustachian tube.

FALSE

The medial part of the tubotympanic recess forms the primitive tympanic cavity.

TRUE

Meckel's cartilage originates from the 2nd pharyngeal arch.

FALSE

According to the classical theory, the stapes is derived from Reichert's cartilage.

TRUE

The lentiform process is found on the malleus and articulates with the stapes.

FALSE

The obturator foramen of the stapes forms after the regression of the stapedial artery.

TRUE

A persistent stapedial artery can cause conductive hearing loss.

TRUE

The tragus is derived from Auricular Hillock 1.

TRUE

Auricular Hillocks 1-3 originate from the 2nd pharyngeal arch.

FALSE

Darwin's Tubercle is considered a congenital ear anomaly found at the junction of the upper and middle thirds of the helix.

TRUE

The intertragal notch is formed from both Auricular Hillocks 1 and 6.

TRUE

The saccule and cochlear duct both originate from the saccular portion of the otic vesicle.

TRUE

The external auditory meatus originates from the 1st pharyngeal pouch.

FALSE

The spiral ganglion of CN VIII is derived from the saccular portion of the otic vesicle.

TRUE

The transformation of auricular hillocks begins from the thoracic region of the embryo.

FALSE

The rami of the mandible help elevate the hillocks to their final position on the head.

TRUE

The tympanic membrane forms from the first pharyngeal membrane.

TRUE

What component of otocyst will foreshadow the formation of the semicircular canals?

Utricle or dorsal component of otocyst

What component of the otocyst will foreshadow the formation of the cochlea?

Saccule or ventral component of otocyst

Name two funcions of the endolymphatic duct and sac.

Sie of inner ear's early phagocytosis and site for CSF formation (and eventual endolymph and perilymph formation)

How many revolutions does the saccular outgrowth undergo?

2 and 1/2

What week AOG is the first turn of the saccular outgrowth formed?

6th week AOG

What week AOG is the second turn of the saccular outgrowth formed?

7th week AOG

What week AOG is the last 1/2 turn of the saccular outgrowth formed?

8th week AOG

TRUE OR FALSE: The tubular outgrowth only forms the cochlear duct.

TRUE

TRUE OR FALSE: The scala tympani is found inside the cochlear duct

FALSE (Should be scala media)

TRUE OR FALSE: The apex of the cochlear duct forms first.

FALSE (Base is formed from the 1st turn, middle from 2nd turn, apex from last half turn)

The spiral tube and cochlear duct foreshadows the formation of?

Membranous labyrinth (with scala vestibuli, scala media, scala tympani)

The penetrating mesenchyme foreshadows formation of?

Osseous labyrinth

TRUE OR FALSE: Canalization or vacuolization begins at the apex

FALSE: It begins at the base/inferior cartilage, moving up the tubular outgrowth. This forms the scala tympani.

TRUE OR FALSE: Canalization continues from apex to base to form the scala vestibuli.

TRUE: This continuation of canalization is marked by the helicotrema, which connects the scala vestibuli and scala tympani.

From which embryological structures do the auricular hillocks arise?

The auricular hillocks arise from the dorsal lateral ends of the 1st and 2nd pharyngeal arches.

What embryonic cells contribute to the formation of auricular hillocks?

Neural crest cells from the 1st and 2nd pharyngeal arches proliferate to form the auricular hillocks

What structure do the auricular hillocks eventually form?

The auricular hillocks condense and combine to form the human pinna (auricle or external ear).

Which auricular hillocks are derived from the 1st pharyngeal arch?

Hillocks numbered 1, 2, and 3.

Which auricular hillocks are derived from the 2nd pharyngeal arch?

Hillocks numbered 4, 5, and 6.

How does the position of the developing auricle change during embryogenesis?

The hillocks elevate from the neck to the lateral aspect of the head or face, influenced by the growth of the mandibular rami

According to most sources, the external auditory canal is derived from which embryologic structure?

The 1st pharyngeal cleft.

When does the epithelial lining of the 1st pharyngeal cleft begin to proliferate and form the meatal plug?

At the beginning of the 3rd month (around the 9th week of age of gestation, AOG).

A solid epithelial plate that temporarily fills the developing external auditory canal

Meatal plug

When does the meatal plug dissolve to form the definitive ear canal?

Around the 7th month of age of gestation (AOG), approximately 2 months before birth.

Otic placodes start to appear as early as what day?

22nd day

What will serve as an immediate anlage for the formation of the semicirculr canals and cochlea?

otocyst / otic vesicle

On what day does the otic pit continues to penetrate the surrounding mesenchyme of the head and neck until it will form a vesicle?

32nd day

The medial wall cells and neural crest cells will form ____ at the level of hindbrain

statoacoustic ganglion

This innervates the hair cells of he forming cochlea for hearing as well as carry auditory type of data coming from the ventral half of the otocyst to the hindbrain

ventral cochlear / spiral ganglion

This innervates the hair cells of the forming semicircular canals for equilibrium and proprioception

dorsal vestibular ganglion / superior ganglion

This carries proprioception data and balancing data from dorsal half of the otocyst to the hindbrain

dorsal vestibular ganglion / superior ganglion

This foreshadows the formation of semicircular canal equipped with endolymphatic duct and sac

dorsal compartmen / utricle

Which compartment of the otocyst foreshadow the formation of cochlea

ventral compartment / saccule

The otic groove continues to invaginate until it forms an otic day on which AOG?

27th day

What is the thickest layer of the cornea

corneal stroma

Which embryologic origin gives rise to the corneal epithelium

Surface ectoderm

Which corneal layers derive from undifferentiated mesodermal cells

Bowman's layer and corneal stroma

Which corneal layers derive from neural crest cells

Descemet's membrane and corneal endothelium

What enzyme leads to dehydration and clearing of the cornea

Hyaluronidase

Central corneal opacity due to incomplete metachromasia or mechanical injury to embryonic cornea

leukoma

When do primordial eyelids begin to form

7th week AOG

When do the eyelid outgrowths fuse

15th week AOG

The fused primordial eyelids will be acted upon by what two genes

hairless gene and FRAS1 gene

Partial fusion of eyelids due to incomplete FRAS1 gene function

ankyloblepharon

Rare congenital anomaly in which the skin is continuous over the eyeball with absence of eyelids

cryptophthalmos

What syndrome is associated with cryptophthalmos and intersex development in the genitals

Fraser-Francois-Feichtiger-Meyer-Ullrich-Schwickerath syndrome

What is the master gene for eye globe formation and lens maturation

PAX-6

What induces upregulation and coexpression of PAX-2

SHH

master gene for optic nerve formation

PAX-2

What condition results if SHH and PAX-2 fail to divide the eye field

Cyclopia or synophthalmia

A congenital disorder or birth defect characterized by the failure of the embryonic prosencephalon or genes involved to properly define the orbits of the eye into two cavities

cyclopia

What gene is upregulated by surface ectoderm and lens placode near each eye field

FGF

What gene is upregulated by the surrounding mesenchyme with mesodermal cells

TGF-β

What is the master gene in the formation of the first 9 layers of the retina

CHX10

Inadvertent fusion of ears

synotia

Inadvertent fusion of eyes

synophthalmia

What is the master gene in the formation of the 10th layer of the retina

MITF gene

What is the master gene for rods and cones formation

CRX gene

Thickened ectoderm plates flanking on either side of the neurolating hindbrain

Otic (Ear) Placodes

Otic Placodes starts to appear at ____ Day

Starts to appear at 22ND DAY AOG

Otic (Ear) Placodes turns into

OTIC PITS

Foreshadow the formation of the inner ear

OTIC PITS

Otic (Ear) Placode cannot self invaginate without genetic instruction (True/False)

False (They Can)

From which embryonic germ layer do the ciliary muscles originate?

Ciliary muscles differentiate from mesodermal cells

Which specific subpart of the Pars Ciliaris Retinae forms the musculatures of the ciliary body?

Pars Muscularis

True/False: The ciliary muscles are responsible for dictating the shape and size of the lens during eye accommodation.

TRUE