Lecture 1- Embryology Flashcards
When does the trilaminar embryo develop?
Forms in 1st 3 weeks of development
What are the 3 components of the trilaminar embryo?
Ectoderm: neural tissue and surface epithelium
Mesoderm: most connective tissues of the body, muscle, bone, and cartilage
Endoderm: lining epithelium of the gastrointestinal, urogenital, and respiratory tract
What arises from the different trilaminar layers?
Otic placodes originate from thickenings of ectoderm
Middle ear originates from endodermal tissue
When do the pharyngeal arches develop?
By 4th week, 5 branchial grooves appear in lower head and neck region on the lateral surfaces
How many pharyngeal arches are there?
5
Which arches contribute to auditory development? Which part of the ear do they contribute to?
Pharyngeal arches 1 and 2 are main contributors to the middle/outer ear
What is the 1st branchial arch responsible for?
Responsible for most of the body structure of the malleus and incus
What is the 2nd branchial arch responsible for?
- Lenticular process of the incus
- Handle of the malleus
- Stapes
When does the auricle begin to develop? What does it arise from?
Develops during 3rd or 4th week from the 1st and 2nd branchial arches
What development occurs during the 3rd week of fetal development?
Inner Ear
- Auditory placode; auditory pit
Middle Ear
-Tubotympanic recess begins to develop
What development occurs during the 4th week of fetal development?
Inner Ear
- Auditory vesicle (otocyst): vestibular-cochlear division
Middle Ear
-5 branchial grooves appear in lower head and neck region on lateral surfaces
Outer Ear
-Tissue thickenings begin to form
What development occurs during the 5th week of fetal development?
Outer Ear
- Primary auditory meatus begins
What development occurs during the 6th week of fetal development?
Inner Ear
- Utricle and saccule present; semicircular canals begin
Outer Ear
-Six hillocks evident; cartilage begins to form
What development occurs during the 7th week of fetal development?
Inner Ear
- One cochlear coil present; sensory cells in utricle and saccule
Outer Ear
- Auricles move dorsolaterally
What development occurs during the 8th week of fetal development?
Inner Ear
- Ductus reuniens present; sensory cells in semicircular canals
- Sensory end organs first appear as localized thickenings of epithelium in the utricle and saccule
Middle Ear
- Incus and malleus present in cartilage; lower half of tympanic cavity formed
Outer Ear
- Outer cartilaginous one-third of external canal formed
What development occurs during the 9th week of fetal development?
Middle Ear
- Three tissue layers at tympanic membrane are present
What development occurs during the 11th week of fetal development?
Inner Ear
- 2.5 cochlear coils present
- Nerve VIII attaches to cochlear duct via ductus reuniens
- Cochlear division of the 8th nerve follows the elongating and coiling of the cochlear duct
What development occurs during the 12th week of fetal development?
Inner Ear
- Sensory cells in cochlea
- Membranous labyrinth complete
- Otic capsule begins to ossify
What development occurs during the 15th week of fetal development?
Middle Ear
- Cartilaginous stapes formed
What development occurs during the 16th week of fetal development?
Inner Ear
- Otic capsule begins to ossify
Middle Ear
- Ossification of malleus and incus beings
What development occurs during the 18th week of fetal development?
Middle Ear
- Stapes begins to ossify
What development occurs during the 20th week of fetal development?
Inner Ear
- Maturation of inner ear; inner ear adult size
Outer Ear
- Auricle is adult shape but continues to grow until age 9
What development occurs during the 21st week of fetal development?
Middle Ear
- Meatal plug disintegrates, exposing tympanic membrane
What development occurs during the 30th week of fetal development?
Middle Ear
- Pneumatization of tympanum
Outer Ear
- External auditory canal continues to mature until age 7
What development occurs during the 32nd week of fetal development?
Middle Ear
- Malleus and incus complete ossification
What development occurs during the 34th week of fetal development?
Middle Ear
- Mastoid air cells develop
What development occurs during the 35th week of fetal development?
Middle Ear
- Antrum is pneumatized
What development occurs during the 37th week of fetal development?
Middle Ear
- Epitympanum is pneumatized
- Stapes continues to develop until adulthood -
- Tympanic membrane changes relative position during first 2 years of life
What are genetic abnormalities?
Thought to be within 1st 2 weeks of development as the zygote
- Chromosomal
- Translocation of chromosomal segments
- Single gene mutation
What are some external ear abnormalities that can be indicative of middle ear bone abnormalities?
Thickened lobes: abnormal incus and stapes
Smaller cup ears w/ absent cartilage: mennonite genetic absences of incus and stapes
Absent superior crus: congenital ossicle fixation
What is anotia?
Occurs when pharyngeal arch hillocks fail to form
- Impacts EAM and ME bones
Known genetic causes: Treacher Collins Syndrome, hemifacial microsomia, congenital aural atresia
What are some characteristics of Treacher Collins Syndrome?
- Downward-slanting eyes
- Small jaw and chin
- Alters development of facial bones and tissues
What is microtia?
Smaller cup ear or overfolded auricle
Can be associated with:
- Hearing and vision abnormalities
- Neurological abnormalities
- Clefting of the face and palate
- Musculoskeletal abnormalities
How does Fetal Alcohol Syndrome (FAS) affect the external ear?
Lower or uneven external ear position
“Railroad track” ear
- Auricle has a curve at the top part of the ear, which is underdeveloped and folded over parallel to the curve beneath
What is FAS associated with?
Delayed auditory function
SNHL
Intermittent CHL due to recurrent serous otitis media
What is absence of the ossicles associated with?
Dwarfism and achondrogenesis
Incus/stapes are most common bones to be absent
Inner ear cochlear and semicircular canal abnormalities are due to what genetic effects?
- The Trisomies
- Michel aplasia (absence of inner ear labyrinth)
- Pendred Syndrome (abnormalities of the cochlea, enlarged vestibular aqueduct, thyroid enlargement)
