Development Of The Ear

Question 1

What is the first indication of the developing ear?

Answer 1

In embryos 22 days a thickening of the surface ectoderm on each side
of the rhombencephalon

Question 2

How are the auditory vesicles (otocysts) formed?

Answer 2

The thickening of the surface ectoderm, the otic placodes, pits ,invaginate rapidly and form the otic or auditory vesicles (otocysts)
• Otic pit, otic vesicle, loses connection from surface ectoderm

Question 3

The inner ear is under inductive influence by?

Answer 3

1. Notochord
2. Paraxial mesoderm

Question 4

Name the embryonic structure tires that develop into the inner ear?

Answer 4

• Otic placode - thickening of ectoderm
• Otic pit
• Otic vesicle = otocyst
Note: Epithelium of membranous labyrinth incl. sensory epithelium originate from ectoderm

Question 5

Each auditory vesicle divided into?

Answer 5

1. Ventral component that gives rise to the saccule and cochlear duct .
2. Dorsal component that forms the utricle, semicircular canals, and endolymphatic duct
   - Together these epithelial structures form the membranous labyrinth.

Question 6

Describe the development of the saccule?

Answer 6

• in the sixth week of development, the saccule forms a tubular outpocketing at its lower pole.
• This outgrowth, the cochlear duct, penetrates the surrounding mesenchyme in a spiral fashion until at the end of the eighth week it has completed 2.5 turns.
• The ductus reuniens connects the remaining portion of the saccule with utricle.

Question 7

What is the cochlear duct?

Answer 7

Outgrowth of the saccule at its lower pole

Question 8

How does the cochlear duct develop?

Answer 8

Penetrates surrounding mesenchyme in a spiral fashion
- completes 2.5 turns at the end of week 8

Question 9

What connects the remaining portion of the saccule with the utricle?

Answer 9

Ductus reuniens

Question 10

What happens to the mesenchyme surrounding the cochlear duct?

Answer 10

Differentiates into cartilage

Question 11

What happens to the cartilaginous shell?

Answer 11

In the 10th week, this cartilaginous shell undergoes vacuolization, and forms two perilymphatic spaces
1. the scala vestibuli
2. scala tympani

Question 12

What separates the cochlear duct from the scala vestibuli?

Answer 12

Vestibular membrane

Question 13

What separates the cochlear duct from the scala tympani?

Answer 13

Basilar membrane

Question 14

Function of spiral ligament?

Answer 14

Attaches lateral wall of cochlear duct to the surrounding cartilage

Question 15

What is the Modiolus?

Answer 15

The median angle of the cochlea angle is connected to and partly supported by a long cartilaginous process know as the modiolus
- the future axis of the bony cochlea

Question 16

Ossification of cartilaginous she’ll happens by?

Answer 16

25 weeks

Question 17

The epithelial cells of the cochlear duct form what 2 ridges?

Answer 17

1. The inner ridge, the future spiral limbus,
2. The outer ridge which forms the sensory cells, hair cells, of the auditory system

• They are covered by the tectorial membrane
• The sensory cells and tectorial membrane together constitute the organ of Corti
• Impulses received by this organ are transmitted to the spiral ganglion and then to the nervous system by the auditory fibers of cranial nerve VIll