Ear & Eye Development Flashcards
When does the ear begin to develop?
4th week
What will the otic vesicle give rise to?
Utricle – forms the endolymphatic duct, utricle and semicircular canals
Saccule – forms the saccule and cochlear duct
What are the specialized hair cells in the ear?
- Cristae ampullaris – in the ampulla of each semicircular canal
- Macula – one in the utricle and one in the saccule
- Cochlear – numerous along the cochlear duct
Spiral ganglion is related to…
Cochlear duct, involved in hearing
Vestibular ganglion is related to…
Remaining hair cells, involved in detection of head movement
What does the otic vesicle signal?
Surrounding mesenchyme to condense and form an otic capsule
What will the otic capsule contribute to?
Petrous part of temporal bone
Rubella infection can cause…
Malformation of cochlea and deafness
What pharyngeal apparatus will contribute to the tympanic membrane?
First pharyngeal groove and pouch
What is the pharyngeal groove lined by? The pouch?
Groove -> endoderm
Pouch -> ectoderm + mesenchyme (mesoderm)
The tympanic membrane is comprised of…
All three germ layers!
Tubotymapnic recess is continuous with…
Mastoid antrum + nasopharynx via pharyngotympanic tube
Tensor tympani embryology
attached to the malleus; it derives from the mesenchyme of the first arch and is innervated by the nerve of the first arch (CN V)
Stapedius embryology
attached to the stapes; it derives from the cartilage of the second arch and is innervated by the facial nerve
What is the external ear innervated by?
CN V + VII
Anotia
Absence of ear
Microtia
Small ear
Auricular appendages
Persistence of extra auricular hillocks, absence of auricle
Preauricular sinuses
Small depressions located anterior to the auricle. This defect results from abnormal closure of the first pharyngeal groove. These sinuses have only cosmetic significance but they can become infected
If cells situated in front of the tympanic membrane fail to die…
Atresia of the external auditory meatus
Atresia of the external auditory meatus
Blockage of the external canal
Congenital cholesteatoma
Epidermoid tissue within the tympanic membrane
The eye develops from four sources
- neuroectoderm – retina, posterior layers of the iris and optic nerve
- surface ectoderm – lens and corneal epithelium
- mesoderm – fibrous and vascular coats
- neural crest – choroid, sclera and corneal endothelium
When does the eye begin to develop?
4th week
What will the lens placode become?
Form lens pits and will invaginate to form a lens vesicle
What will the optic stalk become?
Optic nerve
What will the hyaloid artery become?
Central artery of retina
Where will the retina develop?
The walls of the optic cup
The outer layer becomes the pigmented retina; the inner layer becomes the neural retina
What do the ganglion cells mostly form?
Superficial portion of neural retina
The neural retina and the pigmented retina are separated by…
Intraretinal space
Where does the ciliary body derive from?
Choroid mesenchyme, along with both layers of the optic cup
What are the ciliary muscles derived from?
Choroid mesenchyme from the anterior edge of the optic cup
Where is the iris formed?
Front edge of optic cup
The lens are derived from…
Surface ectoderm that invaginated
The hyaloid artery supplies…
Developing lens
When the hyaloid artery obliterates, the lens becomes…
Avascular
Cornea is formed from…
- Surface ectoderm – corneal epithelium
- Mesoderm – connective tissue
- Neural crest – corneal endothelium
Choroid contributes to the formation of…
The ciliary body
When do the eyelids seperate?
During the 5th to 7th months of development
How do the aqueous chambers form?
Anterior chamber -> between lens & cornea
Posterior chamber -> space in mesenchyme posterior to iris and anterior to the lens
Vitreous body forms in cavity of optic cup
Where are the extrinsic eye muscles formed from?
Prechordal plate mesoderm (preotic somites)
What is the sequence of extrinsic eye muscles?
- lateral and superior rectus
-> the levator palpebrae forms from a splitting of the superior rectus - superior oblique
- medial rectus, inferior rectus and inferior oblique
-> the inferior rectus and inferior oblique form from a common precursor
When does the oculomotor nerve reach the orbit?
early in 5th week
When does the abducens & trochlear nerve reach the orbit?
end of 5th week
Congenital retinal detachment
Recall that the two layers of the retina were separated by an intraretinal space. Normally, there is some degree of fusion between these two layers. If these layers
fail to fuse during development the defect is congenital. Retinal detachment can occur following a blow to the eye in which case fluid can accumulate and vision can be impaired
Coloboma
This defect involves an improper closing of the choroid fissure resulting in a gap in the iris or iris and retina
Cyclopia
This defect occurs when there is fusion of the eye in the midline. Cyclopia is indicated by a single eye; synophthalmia is indicated when there is incomplete fusion of the eyes. Cyclopia results from a defect involving midline structures and is accompanied by other defects and is incompatible
with life. Cyclopia is often accompanied by a midline proboscis that is situated superior to the fused eye
Microphthalmia
This defect is indicated by a small, normal appearing eye or an eye that was arrested at some point during normal development; may lack a lens
Anophthalmia
This defect is indicated by the congenital absence of eye tissue. Can vary in severity – can involve only the optic stalk or may involve development of the forebrain
Persistent pupillary membrane
The pupillary membrane normally covers the anterior surface of the lens and disappears during development. This membrane may remain as strands of connective
tissue spanning the pupil but will rarely interfere with vision
Congenital glaucoma
Glaucoma is any increase in the intraocular pressure. This occurs congenitally when there is a defect in the draining mechanism (scleral venous sinus). This condition may arise in relation to a rubella infection during pregnancy
Congenital cataract
Any lens opacity present at birth; can be progressive so may not be identified at birth; can be caused by infection (rubella, chicken pox, herpes) or genetic
Aniridia
Absence of the iris; defect involving neuroectoderm and neural crest cells
Color of the iris
Usually blue/gray in most newborns -> becomes primary color by 8-10 months
Congenital aphakia
Absence of the lens
Heterochromia
Different eye colors
Retinoblastoma
a neuronal tumor arising from the retina; the most common primary intraocular malignancy of childhood
