Ear development Flashcards
The inner ear develops from
ectodermal otic placode
The external and middle ears arise from
first and second pharyngeal arches and the first pharyngeal cleft and pouch.
When does the Otic Placode first appear?
Week 3-4
The otic placode gradually invaginates to first form
the Otic Pit
then
the Otic Vesicle
Young neurons delaminate from the ventral otocyst to form
statoacoustic (vestibulocochlear) ganglion
statoacoustic (vestibulocochlear) ganglion Splits into?
cochlear and vestibular portions.
Otic Vesicle divides into three things
endolymphatic sac
pars superior (= dorsal, utricular part)
pars inferior (= ventral, saccular part)
Pars superior (utricular): Forms
Semisicular Canals
Ampulla
Urticle
Pars inferior (saccular) Forms
cochlear duct
spiral organ of Corti
saccule
mesenchyme around the otic vesicle to condense and differentiate into
cartilaginous otic capsule
vacuoles appear in the cartilaginous otic capsule
- Which coelse to form perilymphatic space
- Membranus labrinth floats in Perilymph
- Perilymphatic space is comunication with the sub achachnoid space.
The cartilaginous otic capsule later ossifies to form
bony labyrinth of the internal ear (part of the temporal bone).
When does the inner ear reach its adult size?
middle of the fetal period (20-22 weeks)
The tympanic membrane is made up of what types of cells?
Ectoderm of the first pharyngeal groove (outer lining). Endoderm of the tubotympanic recess (inner lining). Mesenchyme (connective tissue) that form the intervening layer between the outer and inner lining. neural crest cells
The first pharyngeal pouch elongates to form:
tubotympanic recess
proximal part of the tubotympanic recess forms the
pharyngotympanic tube (auditory tube or Eustachian tube)
The distal part of the tubotympanic recess expands and becomes the?
tympanic cavity
- which gradually wraps around the small bones of the middle ear-auditory ossicles (malleus, incus, and stapes), their tendons and ligaments, and the chorda tympani nerve
- occures late in pregnancy, 8th month
The malleus and incus arise from
First pharyngeal Arch
The stapes arises from the?
Second pharyngeal arch.
tensor tympani muscle is innervated by
the trigeminal nerve (cranial nerve V),
the stapedius muscle is innervated by the
facial nerve (cranial nerve VII).
tympanic membrane originates from the?
First Pharyngeal Membrain
the tensor tympani (associated with the malleus) and the stapedius (associated with stapes) Form in which week?
9th week from first- and second-pharyngeal arch mesoderm,
external ear consists of ?
- external layer of the tympanic membrane
- external auditory meatus
- the auricle (pinna).
The precursor of the external auditory meatus develops by? What Week?
An invagination of the First Pharangeal Cleft during the 6th week
The Meatel plug fills the External Auditory Meatus until what week>
week 26
When does the Meatus acheave its final length
9-10 years of age.
Auricle develops from what?
six auricular hillocks
auricular hillocks arise during what week Where?
- Week 5
- First and Second Pharyngeal arches.
CHARGE syndrome.
- Coloboma of the eye,
- Heart defects,
- Atresia of the choanae,
- Retarded growth and development,
- Genital and urinary anomalies, and
- Ear anomalies and hearing loss
CH7 Gene issue
- Inner ear defects:
- labyrinthine aplasia,
- reduction in the number of cochlear turns (less than 2.5 turns),
- semicircular canal defects.
- Abnormal development of the middle ear
- External ear abnormalities one of the cardinal features of the syndrome
Defects of the external ear result from what?
abnormal growth and morphogenesis of one or more of the auricular hillocks derived from the first and second pharyngeal arches.
Defects of the middle ear result from?
Results from abnormal formation or ossification of the middle ear ossicles, (themmalleus, incus, and stapes) that are derived from neural crest cells populating the first and second pharyngeal arches.
Suppressed growth of these neural crest cells results in ossicle hypoplasia or aplasia and fixation.
These defects occur in association with skeletal dysplasias such as achondroplasia (FGFR3 mutation) and osteogenesis imperfecta (multiple COLLAGEN mutations), or in various syndromes such as BOR, Treacher Collins, and OAVS.
Large (enlarged) vestibular aqueduct (LVA or EVA)
inner ear dysplasia characterized by enlargement of the bony canal that contains the endolymphatic duct associated with Pendred syndrome gene encodes PENDRIN, a chlorideiodide transporter protein
Genetic defects in the development and function of hair cells can result in what type of hearing defect.
Inner Ear.
Usher syndrome type 1,
- Usher - singer
- sensorineural hearing loss
- retinitis pigmentosa- back wall of eye is damaged.
- autosomal recessive disorder
You can’t hear or see him sing!!
Jervell and LangeNielsen syndrome
sensorineural hearing loss and cardiac arrhythmia (long QT syndrome Accounts for 20-30% nonsyndromic deafness
MTRNR1 gene issues
late onset hearing loss
may be precipitated suddenly by treatment with aminoglycoside antibiotics due to increased sensitivity.
microtia (small auricle)
or
anotia
Suppresed Growth of All Hillocks.
macrotia
(Large Auricle)
Overgrowth of the hillocks
ectopic preauricular tags
Accessory Hillocks present
preauricular pits
Small indentations in front of ear due to accessory Hillocks
Conductive hearing loss
is the result of malformations in the
- external and or
- middle ear
Sensorineural hearing loss
due to genetic causes (Syndromic)
isolated defect (nonsyndromic)
can arise from defects in the inner ear, vestibulocochlear nerve (cranial nerve VIII), or the auditory regions of the brain.
nonsyndromic hearing loss
commonly attributed to environmental factors.
Environmental factors include in utero viral infections (e.g., cytomegalovirus and rubella) and neonatal exposure to aminoglycoside antibiotics (e.g., gentamycin and tobramycin)
syndromic hearing loss
genetic causes
associated with other anomalies about 1/2 of the cases
the first pharyngeal pouch froms?
- Auditory tube
- tympanic middle ear cavity
