10. Development Of The Head And Neck 1

Question 1

In the 4th week of development, what proportion of the embryo does the head and neck represent?

Answer 1

Half.

Question 2

What glands develop from modification of the endoderm tube lining the pharynx in the pharyngeal pouches?

Answer 2

Parathyroid, thymus, palatine tonsils, thyroid.

Question 3

What type of embryological cell are the pharyngeal/brachial arches derived from?

Answer 3

Mesoderm and endoderm.

Question 4

How many pharyngeal/brachial arches are there?

Answer 4

5, numbered 1-6 as the 5th doesn’t form in humans.

Question 5

What constitutes the building blocks for the head and neck region in an embryo?

Answer 5

Frontonasal prominence.

Pharyngeal arches.

Question 6

Which cranial nerves are associated with the pharyngeal arches and supply the derivatives of the arches?

Answer 6

CN V, VII, IX, X.

Question 7

What muscles are derived from Ph Arch 1?

Answer 7

Muscles of mastication of the face.

Question 8

What muscles are derived from Ph Arch 2?

Answer 8

Muscles of facial expression.

Question 9

What muscles are derived from Ph Arch 3?

Answer 9

Stylopharyngeus.

Question 10

What muscles are derived from Ph Arch 4?

Answer 10

Cricothyroid.
Levator palatine.
Constrictors of the pharynx.

Question 11

What muscles are derived from Ph Arch 6?

Answer 11

Intrinsic muscles of the larynx.

Question 12

Each of the pharyngeal arches develops a neural crest-derived cartilage bar. What does each go on to form?

Answer 12

Ph A 1 - meckel’s cartilage, forms the malleus, incus and a template for the formation of the mandible.
Ph A 2 - reicher’s cartilage, forms the stapes plus upper part of the hyoid bone.
Ph A 3 - forms the remainder of the hyoid bone.
Ph A 4 & 6 - forms the cartilages of the larynx.

Question 13

What cavity does the first pharyngeal pouch become?

Answer 13

Tympanic cavity.

Question 14

What does the first pharyngeal cleft become, and what happens to the others?

Answer 14

First cleft - becomes the external acoustic meatus.

Others - second arch grows down to cover the others, obliterating all the other clefts.

Question 15

What can occur if there are remnants of the brachial clefts that should have been obliterated?

Answer 15

Brachial cysts and fistulae can occur on the anterior boarder of sternocleidomastoid.

Question 16

What drives development of the face?

Answer 16

Expansion of the cranial neural tube, appearance of a complex tissue system with the cranial gut tube and outflow of the developing heart, and development of the sense organs with a need to separate the respiratory tract from the GI tract.

Question 17

What components form the face embryologically?

Answer 17

Frontonasal prominence.
Stomatodeum with buccopharyngeal membrane at the centre.
1st pharyngeal arch forms the maxillary prominences and mandibular prominences.

Question 18

What structures does the frontonasal prominence form?

Answer 18

Forehead, bridge of nose, nose, philtrum.

Question 19

What structures does the maxillary prominence form?

Answer 19

Cheeks.
Lateral upper lip.
Lateral upper jaw.

Question 20

What structures does the mandibular prominence go on to form?

Answer 20

Lower lip and jaw.

Question 21

Describe the development of the nose.

Answer 21

Nasal placodes appear on the frontonasal prominence. The maxillary prominences grow medially, pushing the nasal prominences closer together in the midline. These then sink to become the nasal pits, with medial and lateral nasal prominences forming on either side of the pits. Maxillary prominences fuse with the medial nasal prominences, and the medial nasal prominences then fuse in the midline.

Question 22

Fusion of the medial nasal prominences creates the intermaxillary segment, what does this consist of?

Answer 22

Philtrum, 4 incisors and primary palate.

Question 23

How is the main part of the definitive palate formed?

Answer 23

Maxillary prominence gives rise to two palatal shelves. These grow vertically downwards into the oral cavity on each side of the developing tongue. The mandible grows large enough to allow the tongue to drop. The palatial shelves then grow towards each other and fuse in the midline. The nasal septum develops as a midline down-growth and ultimately fuses with palatial shelves.

Question 24

What causes a lateral cleft lip?

Answer 24

Failure of fusion of the medial nasal prominence and maxillary prominence.

Question 25

What causes a cleft lip and cleft palate?

Answer 25

Failure of fusion of the medial nasal prominence and maxillary prominence, combined with failure of palatial shelves to meet in the midline.

Question 26

What do the auricles develop from?

Answer 26

Proliferation within the isn’t and 2nd Ph Arches surrounding the meatus.

Question 27

Describe how the ears become correctly positioned

Answer 27

External ears develop initially in the neck. As the mandible grows the ears ascend to the side of the head to lie in line with the eyes.

Question 28

What abnormality do all common chromosomal abnormalities have associated with them?

Answer 28

External ear anomalies.

Question 29

Why is the face affected in foetal alcohol syndrome?

Answer 29

Facial skeleton is derived from neural crest cells populating the pharyngeal arches. Neural crest irrational and development of the brain are extremely sensitive to alcohol, leading to behaviour and facial defects.

Question 30

Name 4 facial defects seen in fetal alcohol syndrome

Answer 30

Small head.
Epicanthal folds.
Flat mid face.
Smooth philtrum.
Underdeveloped jaw.
Thin upper lip.
Short nose.
Small eye openings.
Low nasal bridge.