Week 3 - Ach (Embryo of Eye & Ear) Flashcards
When does the otic placode appear?
around Day 22
What are the general derivatives of the otic placode?
- Inner Ear
- Otic Vesicle => MEMBRANOUS Labyrinth
- Utricle –> Semicircular Duct
- Saccule –> Cochlear Duct
- Otic Capsule => BONY Labyrinth
- Semicircular Canals
- Cochlea
- Vestibule
- Otic Vesicle => MEMBRANOUS Labyrinth
What area of the primitive brain do the otic placodes arise?
Mylencephalon
What dermal layer thickens to form the otic placodes?
Ectoderm
How do the otic vesicles form?
- Otic pits invaginate in each otic placode
- Otic pits sink into underlying mesoderm and detach from the surface ectoderm
What does each otic vesicle form?
- Epithelial structures of the inner ear
- Membranous labyrinth
- Dorsal part
- Utricles
- Semicircular Ducts
- Endolymphatic duct
- Ventral part
- Saccules
- Cochlear Ducts
- Ductus reuniens
- Dorsal part
- Membranous labyrinth
How does the bony (osseous) labyrinth form?
Mesoderm surrounding otic vessicle –>
condenses into cartilaginous otic capsule –>
becomes bony labyrinth via endochondral ossification
What is the Statoacoustic Ganglion formed by?
Cells from the wall of the otic vesicle and neural crest cells.
What do the tympanic cavity and Eustachian tube form from?
Endodermal origin from 1st pharyngeal pouch
(tubotympanic recess)
What cartilage do the ossicles form from?
Malleus and Incus –> dorsal tip of 1st pharyngeal arch (Meckel’s cartilage)
Stapes –> 2nd pharyngeal arch (Reichert’s cartilage)
What middle ear muscle/nerve derives from the 1st pharyngeal arch?
Tensor tympani - CN V3
What middle ear muscle/nerve derives from the 2nd pharyngeal arch?
Stapedius - CN VII
The external ear is derived from what pharyngeal cleft derivative?
1st
What are the three embryologic layers of the Tympanic Membrane?
- Ectodermal outer layer - 1st pharyngeal groove
- Mesodermal middle layer - 1st & 2nd pharyngeal
- Endodermal inner layer - 1st pharyngeal
What embryological processes can cause neurosensory deafness?
- Abnormal development of:
- cochlea
- CN VIII
- brainstem
- Rubella in 1st trimester
- Neural crest deficit (essential in stria vascularis)
What embryological processes can cause conduction deafness?
- Persistance of meatal plug
- Fixation of footplate of stapes
- annular ligament failure
- Abnormalities of malleus and incus
Describe the development of the optic cup from the diencephalon.
- Neuroectoderm of the Diencephalon
- Optic grooves
- Optic vesicles
- Optic Cup
What are the 8 basic derivatives of the optic cup?
- Retina
- Iris
- Lens
- Vitreous/Aqueous humor
- Choroid/Sclera
- Cornea
- Conjunctiva
- Eyelids
The optic nerve is a tract of what?
the Diencephalon
Hyaloid vessels are branches of what? What do they supply?
Branches of the Ophthalmic Vessels
Supply:
- Optic Nerve
- Retina
- Posterior aspect of the Lens Capsule
What process inolving the optic nerve continues after birth?
Myelination
When does the Hyaloid artery normally regress?
11 weeks - 8 months
What is a congenital coloboma?
Defective closure of the choroid or optic fissure.
Where is a Congenital Coloboma positioned?
infero-nasal quadrant
(reflective of the location of the optic fissure during fetal development)
What two layers of the optic cup become the retina? What do each become?
- Thin outer layer
- Retinal pigmented epithelium (RPE)
- Thick inner neural layer
- Photoreceptors
- Bipolar/Ganglion cell layers
(layers separated by Intraretinal Space that disappears around week 6)
What may a congenital detached retina be due to?
The failure of the retinal layers to fuse and obliterate the intraretinal space.
(or by unequal growth of the eye)
What is Microphthalmia?
Arrested development of the optic vesicle
(globe is small & lens does not form)
What is Anophthalmia?
Arrested development of the optic vesicle early in Week 4.
Usually accompanies severe craniocerebral defects.
What causes congenital glaucoma?
Malformed drainage apparatus
or
Rubella
What embryological tissue is the lens derived from?
Ectoderm
