Embryology Flashcards
What develops from the ectoderm?
membraneous labyrinth (inner ear), auricular skin, eam lining
Mesoderm develops into?
3 ossicles, 2 muscles of the ear, fibrous layer of the TM, optic capsule, osseus labyrinth
Endoderm development?
Middle ear space & Eustachian tube
What is the invagination process of the inner ear
Auditory placode –> optic pit –> otocyst (2 divisions saccule and utricle) –> inner ear
What is the notochord?
Primitive spinal cord, that directs the invagination of the neural tube
What occurs on week 3 of gestation?
Notochord forms, and the neural groove forms.
What happens on week 4 of gestation?
The neural tube closes & otic pits form (bronchial arches). Mouth, liver and lungs form. Heart begins to beat.
What conditions can occur on the week 4 gestation
Anencephaly (lack of a brain) neural tube closure dysfunction. Mouth disruption can result in cleft palate. Hydrocephaly can happen in this stage as well (4th ventricle) or Spina bifida if the closure has anomalies
Week 5 of gestation
Circulation begins and brain divides into 5 vesicles
Week 7 of gestation (week 6-9)
The cochlea forms 1 full turn. Hillocks start creating the pinna.
Week 8-10 of gestation
mass creation of neurons, the cochlea is formed out of the saccule, genitals appear, cochlea has done full 2.5 turns
Week 20-25 of gestation
At 21 weeks the cochlea is fully formed. Functioning inner ear, respiratory able to support gas exchange.
Pharyngeal Arch 1 (mandibular) 2 hillocks
Forms the Pinna. Develops into 1. Tragus and 2. Crux of Helix.
Pharyngeal Arch 2 (hyoid) 4 hillocks
- ascending helix
- upper helix, scaphoid, and anti-helix
- descending helix, middle scaphoid, and anti-helix
- anti tragus
Pharyngeal Arch 1 (Middle ear)
Meckell’s cartilage;
- head of the malleus
- short process and body of the incus
- tensor tympani (CN5)
Pharyngeal Arch 2 (Middle ear)
Reichert’s cartilage;
- handle of the malleus
- long process of the incus
- super structure of the stapes
- tympanic part of the stapes footplate
- stapedius muscle (CN7)
Cartilage Ossicles timeline
incus and malleus - week 8.5
stapes - week 15
Ossification of the Ossicles timeline
incus and malleus 15-32 weeks
stapes 18 weeks an beyond
The otocyst is directed by what? and how?
Hindbrain; releases neurotransmitters
Fetus can respond to sound at which week?
26-28 weeks
At what day does the endolymphatic duct, utricle, and saccule specify
36 days
endogenous vs exogenous
endogenous is within the cortex, starts off as irregular firing of action potentials, becomes regular at 22 weeks in response to sound
Exogenous: needs stimulation from the outside to promote tonotopic organization within the auditory system; IHC develop before OHC
How do the frequencies develop in threshold and f discrimination? when does f discrimination occur?
high to low; f discrimination emerges at 6 months (adult like)
