What is meant by the neural crest?
A specialised population of cells that originates within the neuro-ectoderm.
Cells of the lateral border of the neuro-ectoderm become displaced and enter the mesoderm
What are the embryonic tissue components of the face?
Maxillary and mandibular prominences from the 1st PA
What external features does the frontonasal prominence form?
Forehead, bridge of nose, nose and philtrum
What external features does the maxillary prominence form?
Cheek, lateral upper lip and lateral upper jaw
What external features does the mandibular prominence form?
Lower lip and jaw
What happens in the development of the nose?
Nasal placodes appear on the Frontonasal Prominence
They then sink to become the nasal pits and medial and lateral nasal prominences form on either side of the pits.
The maxillary prominences grow medially, which pushes the nasal prominences closer together in the midline.
The maxillary prominences fuse with the medial nasal prominences and the medial nasal prominences then fuse in the midline.
How do we create the intermaxillary segment?
What does it give rise to?
By the fusion of the medial nasal prominences
It separates the nostrils from the mouth
It gives rise to the philtrum, medial part of the maxillary bone, 4 incisor teeth and the primary palate
How are the nasal and oral cavities separated?
The oronasal membrane, which ruptures
The cavities are initially separated by primary palate
The cavities are then separated by the secondary palate
How do we form the secondary palate?
The maxillary prominence gives rise to 2 palatal shelves.
They grow down vertically in to the oral cavity on each side of the developing tongue.
The mandible needs to grow larger enough to allow the developing tongue to drop out of the way.
The palatal shelves then grow towards each other and fuse in the midline and to the nasal septum
What is meant by a lateral cleft lip?
Failure of the medial nasal prominence and maxillary prominence to fuse
What is meant by cleft lip and palate?
Cleft lip and failure of palatal shelves to meet in the midline.
It can involve the primary or secondary palate.
What happens in the development of the eyes?
4th week, out-pocketings of forebrain.
The optic placode will form the lens of the eye.
The outgrowth create optic vesicles, they grow out towards the surface and make contact with the lens placode.
The lens placode then invaginates and pinches off
What happens in the positioning of the eyes?
Eye primordia are positioned on the side of the head.
As the facial prominences grow, the eyes move to the front of the face
What happens in positioning of the ears?
The external ears develop initially in the neck. There are proliferations within the first and second pharyngeal arches called auricular hillocks. As the mandible grows. The ears ascend to the side of the head to lie in line with the eyes
What happens in the development of hearing and balance?
Development from otic placodes
They invaginate to form auditory vesicles, which develop to form the membranous labyrinth to give rise to the cochlea and semi-lunar canal system
What is the importance of foetal alcohol syndrome?
Alcohol freely passes across the placenta
There is no known safe level of alcohol consumption during pregnancy
Neural crest migration and brain development are extremely sensitive to alcohol