Face and Nose Development

Question 1

Where are neural crest cells initially found?

Answer 1

Neural crest cells are initially formed during the creation of the neural tube. As the ectoderm invaginated, ridges form above the neural tube where the 2 edges of ectoderm meet. The peak of these ridges is where the neural crest cells are first found

Question 2

Name 4 main facial features that must develop in the fetus.

Answer 2

Philtrum, Nares, Oral fissure, Palpbral fissures (eye sockets)

Question 3

What is the stomatodeum?

Answer 3

A depression in the middle of the future face that will become the future mouth. 5 prominences form around it.

Question 4

Name the 5 prominences that form around the stomatodeum.

Answer 4

Frontonasal prominence (FNP), maxillary prominences (2), mandibular prominences (2)

Question 5

What parts of the face are derived from the FNP?

Answer 5

Forehead, bridge of the nose, nose, philtrum

Question 6

What parts of the face are derived from i) the maxillary ii) the mandibular prominences?

Answer 6

i) maxillary: cheeks, lateral lip and upper jaw

ii) mandibular: lower lip and jaw

Question 7

What is a placode?

Answer 7

A thickened area of ectoderm

Question 8

Describe in 3 steps the formation of the nose from the nasal prominences.

Answer 8

1) the maxillary prominences start to grow, pushing the nasal provinces closer together
2) the maxillary prominences fuse with the medial nasal prominences
3) the medial nasal prominences fuse together at the midline

Question 9

What 3 things comprise the intermaxillary segment?

Answer 9

Philtrum, primary palate, the upper jaw (4 incisors)

Question 10

Describe the origin, growth and outcome of the palatal shelves.

Answer 10

The palatal shelves grow vertically down from the maxillary prominences towards the growing tongue

The mandible then grows allowing the tongue to drop and creating space for the shelves to grow

The shelves then grow horizontally towards the midline and fuse, forming the roof of your mouth and a ridge that can still be felt down the centre

Question 11

Where are the:

i) primary palate and philtrum
ii) secondary palate derived?

Answer 11

i) nasal prominences

ii) maxillary prominences

Question 12

Describe the difference between why a lateral cleft lip, and a cleft lip and palate occur.

Answer 12

A lateral cleft lip occurs due to the failure of fusion between the medial nasal prominence and the maxillary nasal prominence

A cleft lip and palate is this plus failure of fusion of the palatal shelves along the midline

Question 13

What are optic placodes and what do they go on to form?

Answer 13

Optic placodes are thickened ectoderm that are pushed from underneath by out pocketing of the forebrain during the formation of the eyes. They go onto form the lens of the eye:

1) forebrain out pockets, pushing up on the otic placodes
2) the placode ectoderm invaginated, then pinch off and sit in the centre of the forebrain out pocketings

Question 14

What tissues are the i) retina ii) lens derived from?

Answer 14

i) retina: forebrain

ii) lens: optic placodes (ectoderm)

Question 15

Growth of what moves the eyes from the side of the head to a binocular vision position?

Answer 15

Growth of the facial prominences

Question 16

In the external development where are the external auditory meatus, and auricle derived from individually?

Answer 16

i) external auditory meatus grows from the 1st pharyngeal arch
ii) auricle grows from the 1st and 2nd PAs

Question 17

Where is the initial position of the ear, why is this, and how does it move?

Answer 17

The initial position of the ear is on the neck due to it growing from the 1st pharyngeal arch

It ascends to be in line with the eyes due to the growth of the mandible

Question 18

Briefly describe the formation of the inner ear tubes.

Answer 18

Otic placodes on the ectoderm sink forming the auditory vessels

Question 19

In fetal alcohol syndrome (FAS) what are the 3 common facial feature alterations?

Answer 19

Smooth philtrum, thin upper lip, small eye openings

Question 20

What cells are particularly sensitive to alcohol levels in the developing fetus?

Answer 20

Neural crest cells