Embryology

Question 1

What develops from the ectoderm?

Answer 1

membraneous labyrinth (inner ear), auricular skin, eam lining

Question 2

Mesoderm develops into?

Answer 2

3 ossicles, 2 muscles of the ear, fibrous layer of the TM, optic capsule, osseus labyrinth

Question 3

Endoderm development?

Answer 3

Middle ear space & Eustachian tube

Question 4

What is the invagination process of the inner ear

Answer 4

Auditory placode –> optic pit –> otocyst (2 divisions saccule and utricle) –> inner ear

Question 5

What is the notochord?

Answer 5

Primitive spinal cord, that directs the invagination of the neural tube

Question 6

What occurs on week 3 of gestation?

Answer 6

Notochord forms, and the neural groove forms.

Question 7

What happens on week 4 of gestation?

Answer 7

The neural tube closes & otic pits form (bronchial arches). Mouth, liver and lungs form. Heart begins to beat.

Question 8

What conditions can occur on the week 4 gestation

Answer 8

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

Question 9

Week 5 of gestation

Answer 9

Circulation begins and brain divides into 5 vesicles

Question 10

Week 7 of gestation (week 6-9)

Answer 10

The cochlea forms 1 full turn. Hillocks start creating the pinna.

Question 11

Week 8-10 of gestation

Answer 11

mass creation of neurons, the cochlea is formed out of the saccule, genitals appear, cochlea has done full 2.5 turns

Question 12

Week 20-25 of gestation

Answer 12

At 21 weeks the cochlea is fully formed. Functioning inner ear, respiratory able to support gas exchange.

Question 13

Pharyngeal Arch 1 (mandibular) 2 hillocks

Answer 13

Forms the Pinna. Develops into 1. Tragus and 2. Crux of Helix.

Question 14

Pharyngeal Arch 2 (hyoid) 4 hillocks

Answer 14

1. ascending helix
2. upper helix, scaphoid, and anti-helix
3. descending helix, middle scaphoid, and anti-helix
4. anti tragus

Question 15

Pharyngeal Arch 1 (Middle ear)

Answer 15

Meckell’s cartilage;

1. head of the malleus
2. short process and body of the incus
3. tensor tympani (CN5)

Question 16

Pharyngeal Arch 2 (Middle ear)

Answer 16

Reichert’s cartilage;

1. handle of the malleus
2. long process of the incus
3. super structure of the stapes
4. tympanic part of the stapes footplate
5. stapedius muscle (CN7)

Question 17

Cartilage Ossicles timeline

Answer 17

incus and malleus - week 8.5

stapes - week 15

Question 18

Ossification of the Ossicles timeline

Answer 18

incus and malleus 15-32 weeks

stapes 18 weeks an beyond

Question 19

The otocyst is directed by what? and how?

Answer 19

Hindbrain; releases neurotransmitters

Question 20

Fetus can respond to sound at which week?

Answer 20

26-28 weeks

Question 21

At what day does the endolymphatic duct, utricle, and saccule specify

Answer 21

36 days

Question 22

endogenous vs exogenous

Answer 22

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

Question 23

How do the frequencies develop in threshold and f discrimination? when does f discrimination occur?

Answer 23

high to low; f discrimination emerges at 6 months (adult like)