Head and Neck: Development of the Face and Nose

Question 1

What drives development of the face?

Answer 1

Expansion of the cranial neural tube - need normal development of the brain

Question 2

What is the embryological reasoning why their is a soft palate and a hard palate?

Answer 2

Initially the resp tract develops as an out-pouch of the GI tract where the opening was the GI tract. The separation causes the soft and hard palate

Question 3

What is the neural crest?

Answer 3

A specialised collection of cells that are derived from the neuroectoderm. They fold to create the neural tube so therefore are critical for the development of the head and neck.

Question 4

What is the palpebral fissure and the philtrum?

simple)

Answer 4

The palpebral fissure is the opening to the orbital cavity

The philtrum is the groove above the top lip

Question 5

Which pharyngeal arches make up the face?

Answer 5

• Neural crest of 1st arch makes the facial skeleton
• Mesoderm of 1st arch makes the muscles of mastication
• Mesoderm of 2nd arch makes the muscles of facial expression
  (explains why sensation of face and mastication muscles are trigeminal nerve and muscles of facial expression are facial nerve)

Question 6

What are the features of the frontonasal prominence?

Answer 6

Its prominent due to underlying developing brain

It contains the nasal placodes and the primordia of the eyes

Question 7

What is the stomatodeum?

Answer 7

A small depression in the face - the buccopharyngeal membrane is at the centre (no layer between endo and ectoderm)

Question 8

What are the 4 prominences making up the face?

Answer 8

The frontonasal prominence
the maxillary and mandibular prominence (1st arch)
The stomatodeum

Question 9

What external features of the face are made up of the 3 prominences?

Answer 9

Frontonasal prominence: forehead, nose, philtrum
Maxillary prominence: cheeks, lateral upper lip and lateral upper jaw
Mandibular prominence: lower lip and jaw

Question 10

Outline the development of the external nose

Answer 10

Nasal placodes appear on the FNP and sink to become nasal pits
Medial and lateral nasal prominences form on either side of the pits
The maxillary prominences then grow medially which pushes the nasal prominences to the midline. The medial prominences get pushed together and fuse

Question 11

What is the oronasal membrane?

Answer 11

A connective tissue layer that ruptures so theres continuity between the nasal and oral cavity

Question 12

Outline the developement on the nasal cavity

Answer 12

The nasal septum grows down into the oral cavity and the maxillary prominence gives rise to 2 palatal shelves which grow down into the oral cavity each side of the tongue.
As the jaw grows there is enough space for the tongiue to drop and the 2 palatal shelves fuse in the midline along with the nasal septum

Question 13

What is the origin of the palate?

Answer 13

The primary palate and philtrum are made of the intermaxillary segment (medial nasal prominences)
The rest of the palate is the fused palatal shelves from the maxillary process

Question 14

How does a cleft lip and palate occur?

Answer 14

A lateral celft lip affects just the lip and can extend to the nose. It is due to failure of the medial nasal prominence and maxillary prominence to fuse.

A cleft lip and palate also affects the primary or secondary palate. It is a filaure of the palatal shelves to fuse in the midline

Question 15

What week do the eyes begin to develop?

Answer 15

The 4th week

Question 16

Outline the development of the eyes

Answer 16

The eyes are out pouches of the forebrain which grow out to make contact with the lens placode. The lens placode then thickens and invaginates.
(the lens is derived from the placode, the retina is derived from the forebrain)

Question 17

The eys begin on the side of the head, how do they move round to the front?

Answer 17

The facial prominences grow which push the eyes round to the front for binocular vision

Question 18

Which arches is the external ear derived from?

Answer 18

The external auditory meatus develops from the 1st pharyngeal cleft (only cleft that remains)
The auricles develop from the 1st and 2nd pharyngeal arches

Question 19

How does the position of the ears change through development?

Answer 19

The ears initially develop in the neck, however as the mandible grows the ears ascend to become in line with the eyes.
All common chromosomal abnoramlies have external ear abnormalities eg in downs syndrome the ears are small with over folded helices

Question 20

What is fetal alcohol syndrome?

Answer 20

Neural crest cells are really sensitive to alcohol which crosses the placenta easily. Fetal alcohol syndrome causes mental and physical abnormalities, however alcohol related neurodevelopmental delay occurs with less alcohol