Week 3 Flashcards
3 stage of human prenatal development
- pre-embryonic (week 1-3)
- Embryonic (week 4-8)
- Fetal (week 9- birth)
pre-embryonic
week 1
zygote cleaves and forms blastocyst which forms hypoblast
pre-embryonic week 2
bilaminar disc formation
form layer of epiblast
Preembryonic week 3
when the neural development starts in 3 weeks
- notochord and neural plate
when does the outer and middle ear form
embryonic stage and much later
middle ear formation
forms from the 1st and 2nd branchial arch
- some structures come from both
most common isolated congenital anomaly
disconnection between incus and stapes, long process of incus absent or abnormal, and super structures of stapes is malformed
bones don’t fuse together
cause congenital conductive HL
malformation of ossicular chain occurs as a solitary lesion T/F
False it rarely occurs as a solitary lesion there is usually other temporal bone anomalies (Atresia of EAC)
Development of pinnae
begins at 4 weeks
- at 3 months more mature ossicles develop quite rapidly
cochlear development
starts at 7 weeks (1 turn)
10-11 weeks 2 1/2 turns
25 weeks fully mature
- organ of corti develops from thickened epitheial cells of cochlear duct
when is the first sign of hair cell differentiation
9-10 weeks
what shape is IHC
start cylindrical and become flattened shape
are IHC or OHC immature for a longer period of time
OHCS
how many rows of hair cells exist initially
2 IHC 4 OHC, overproduction followed by reabsorption may serve to slow development
3 stages of HC innervation
- before onset of function- IHC receive efferent and afferent OHC only efferent
- onset of function
- adult like- IHC strong afferent innervation and OHC receive large efferent connections
anotia
absent pinna, 10dB hearing loss (conchae gives gain of approx 10dB at 5KHz)
stenois
partial closure of ear canal
atresia
complete closure of ear canal
how much of a dB loss can a complete ear canal closure cause
50-60dB conductive hearing loss
microtia
congenital birth defect of outer ear due to incomplete development of 1st and 3nd brachial arches before 5th week of gestation
what are the syndromes associated with microtia
treacher collins
fraser
nager
goldenhar
satyr ear
pinna comes out to sharp point and forward fold
- deficiency in 4th hillock during 6th and 8th week gestation
- potential localization and conductive loss issues
stahl ear
abnormality in superior crus on antihelix
- may have 3rd crus
less elastic cartilage
lop ear
folding down of helix and scapha
question mark ear
cleft between helix and lobe
- defect between 5th and 6th hillocks
- occurs b.w 6th and 8th week gestation
Darwin tubricle
small growth at superior point of pinna due to small growth in position of 5th hillock
- autosomal dominant trait
what % of congenital deafness is attributable to recessive genetic factors
80-85%
what % of congenital deafness is attributable to dominant genetic factors
10%
what % of congenital deafness is attributable to mitochondrial mutations
5%
what % of congenital hearing loss is syndromic vs non-syndromic
30% syndromic
70% non-syndromic
waardenburg syndrom
-moderate-profound hearing loss
-2 different coloured eyes or unusally bright blue
-white forelock premature graying
- low frontal hairline
- wide space inner corners of eyes
ushers
autosomal recessive
3-6% deaf and 3-6% hearing impaired
- type I most severe
Type III least severe
night blindness is associated with what type of ushers
Type III
Type III ushers hearing loss onset is when
mid teens deaf by mid-late adult
ushers Type II
Moderate to severe hearing loss
- do well with amplification
Type I ushers
profound HL and severe balance issue with little oral language (sign) and rarley walk before 18 months
- progress to blindness
non-syndromic hearing losses
COCH mutation
GJB2-Gap junction beta 2
Connexin
COCH mutation
vestibular problem
onset 15-65 years
GJB2-Gap junction beta 2
most common cause HL
encodes protein connexin lining gap junction
varying degrees of HL from mild- profound
HL @ birth or shortly after
mumps
low incidence of HL
tinnitus and fullness common
hearing loss within 2 weeks of inflammation of parotid gland, rapid onset, profound loss and permanent
measles
was the most common cause of HL before vaccine
- now low incidence
if you did get it 45% deaf 55% mild to. moderate
what is the inutarine background noise
28dBsPL, mostly less 40HZ
external sounds that are attenuated in fetal environment
<250 0-2dB
1KKhZ 20dB
2-4KHZ 40dB
asphyxia
lack of oxygen in utero and postnatally can cause HL
