S6) Development of the Head, Neck and Face

Question 1

Describe the structure of the pharyngeal arches

Answer 1

Pharyngeal arches are comprised of a system of mesenchymal proliferations in the neck region of the embryo

Question 2

How many pharyngeal arches are there?

Answer 2

5 in total, numbered 1 to 6 (5th does not form in humans)

Question 3

Identify the components which constitute the building blocks for the head and neck region

Answer 3

• Pharyngeal arches
• Frontonasal prominence (FNP)

Question 4

Describe the association of the cranial nerves with the pharyngeal apparatus

Answer 4

• Cranial nerves – CN V, CN VII, CN IX & CN X
• Functions:

I. Mixed sensory & motor functions

II. Supply the derivatives of the pharyngeal arches

Question 5

Describe how the muscles of the face are derived from the pharyngeal arches

Answer 5

• Ph Arch 1: muscles of mastication
• Ph Arch 2: muscles of facial expression

Question 6

State the 3 muscles derived from the 4th pharyngeal arch

Answer 6

Ph Arch 4:

• Cricothyroid
• Levator palatini
• Constrictors of the pharynx

Question 7

State the muscles derived from the 3rd and 6th pharyngeal arches

Answer 7

• Ph Arch 3: stylopharyngeus
• Ph Arch 6: intrinsic muscles of the larynx

Question 8

Each of the pharyngeal arches develops a neural crest.

Identify the cartilages of the 1st & 2nd pharyngeal arches

Answer 8

- Ph Arch 1 – Meckel’s cartilage: malleus, incus + a template for formation of the mandible

- Ph Arch 2 – Reichert’s cartilage: stapes + upper part hyoid bone

Question 9

Each of the pharyngeal arches develops a neural crest.

Identify the cartilages of the 3rd, 4th & 6th pharyngeal arches

Answer 9

- Ph Arch 3 – remainder of hyoid bone

- Ph Arch 4 & 6 – cartilages of the larynx

Question 10

The aortic sac lies in floor of the pharynx.

Hence, in light of this describe the derivatives of the pharyngeal arch arteries

Answer 10

- Ph arch 1&2 arteries disappear

- Ph arch 3 artery = internal carotid artery

- Ph arch 4 artery = arch of aorta (L) & subclavian artery (R)

- Ph arch 6 artery = pulmonary arteries

Question 11

What is a pharyngeal pouch?

Answer 11

Pharyngeal pouches are endoderm lined pockets in the pharynx

Question 12

The first pharyngeal pouch is the largest.

What is its derivative?

Answer 12

Pharyngotympanic tube and middle ear cavity

Question 13

What is the derivative of the second pharyngeal pouch?

Answer 13

Palatine tonsils

Question 14

What are the derivatives of the third pharyngeal pouch?

Answer 14

• Inferior parathyroid
• Thymus gland

Question 15

What are the derivatives of the fourth pharyngeal pouch?

Answer 15

• Superior parathyroid gland
• C cells of thyroid gland

Question 16

What is a pharyngeal cleft?

Answer 16

Pharyngeal clefts are grooves which form in the lateral ectodermal surface of the neck region to separate the arches

Question 17

Describe the fate of the first pharyngeal cleft

Answer 17

1st pharyngeal cleft is remains and becomes the external acoustic meatus

Question 18

What happens to the other pharyngeal clefts (besides 1)?

Answer 18

Ph arch 2 grows down to cover others, obliterating all other clefts

Question 19

Which conditions can occur if there are remnants of other pharyngeal clefts?

Answer 19

Branchial cysts or fistulae can occur

Question 20

Identify 5 muscular derivatives of pharyngeal arch 1

Answer 20

• Muscles of mastication
• Mylohyoid
• Anterior belly of digastric
• Tensor tympani
• Tensor veli palatine (soft palate)

Question 21

Identify 5 skeletal derivatives of pharyngeal arch 1

Answer 21

• Maxilla
• Zygoma
• Meckel’s cartilage: mandible, malleus, incus

Question 22

Identify 4 muscular derivatives of pharyngeal arch 2

Answer 22

• Muscles of facial expression
• Stapedius
• Stylohyoid
• Posterior belly of digastric

Question 23

Identify 4 skeletal derivatives of pharyngeal 2

Answer 23

Reichert’s cartilage:

• Superior part of hyoid
• Stapes
• Styloid process
• Stylohyoid ligament

Question 24

What is the muscular derivative of pharyngeal arch 3?

Answer 24

Stylopharyngeus muscle

Question 25

What is the skeletal derivative of pharyngeal arches 3 and 4?

Answer 25

Epiglottis

Question 26

Identify the 3 muscular derivatives of pharyngeal arches 4-6?

Answer 26

- Constrictor muscles of pharynx and muscles of soft palate (levator veli palatine) - Muscles of the larynx - Striated muscle of upper oesophagus

Question 27

What is the skeletal derivative of pharyngeal arches 4-6?

Answer 27

Cartilages of the larynx

Question 28

Which 4 events drive the development of the face?

Answer 28

- The expansion of the **cranial neural tube** - The appearance of a **complex tissue system** - The development of the **sense organs** - The need to **separate** the respiratory tract from the GI tract

Question 29

What is associated with the appearance of a complex tissue system in the development of the face?

Answer 29

- The cranial gut tube - The outflow of the developing heart

Question 30

Identify and describe 2 structures which form in the early development of the face

Answer 30

- Facial primordia I. Derived from Ph arch 1 II. Contains FNP - Primordia of eyes

Question 31

What does the FNP do in the facial primordia?

Answer 31

**Frontonasal prominence** surrounds ventro-lateral part of the forebrain

Question 32

Identify the 4 components of the developing face

Answer 32

- Frontonasal prominence - Maxillary prominence (PhA 1) - Mandibular prominence (PhA 1) - Stomatodeum (depression in buccopharyngeal membrane)

Question 33

Identify 4 major facial features

Answer 33

- Palpebral fissures - Oral fissure - Nares - Philtrum

Question 34

Identify the 4 components of the frontonasal prominence

Answer 34

- Forehead - Bridge of nose - Nose - Philtrum

Question 35

Identify the 3 components of the maxillary prominence

Answer 35

- Cheeks - Lateral upper lip - Lateral upper jaw

Question 36

Identify 2 components of the mandibular prominence

Answer 36

- Lower lip - Lower jaw

Question 37

In 5 steps, describe the embryological development of the nose

Answer 37

⇒ **Nasal placodes** appear on the FNP & sink to become the **nasal pits** ⇒ **Medial** and **lateral nasal prominences** form on either side of the pits ⇒ **Maxillary prominences** grow medially, pushing the nasal prominences closer together in the midline ⇒ Maxillary prominences **fuse** with medial nasal prominences ⇒ Medial nasal prominences then **fuse in the midline**

Question 38

In 2 steps, describe the development of palatal shelves

Answer 38

⇒ Maxillary prominence give rise to **two palatal shelves** ⇒ These grow vertically downwards into the **oral cavity** on each side of developing tongue

Question 39

In 2 steps, explain how the oral and nasal cavities are separated

Answer 39

⇒ Fusion of medial nasal prominences creates the **intermaxillary segment** ⇒ The secondary palate is derived from palatal shelves

Question 40

State the 3 components of the intermaxillary segment

Answer 40

- **Labial component:** philtrum - **Upper jaw:** 4 incisors - **Palate**: primary palate

Question 41

In 3 steps, explain how the nasal septum is formed

Answer 41

⇒ The **mandible** grows large enough to allow the tongue to “drop” ⇒ The **palatal shelves** then grow towards each other and fuse in the midline ⇒ The **nasal septum** develops as a midline down-growth & ultimately fuses with palatal shelves

Question 42

How does a cleft lip occur?

Answer 42

**Lateral cleft lips** are due to the failure of fusion of the medial nasal prominence with the maxillary prominence

Question 43

How does a cleft lip and cleft palate occur?

Answer 43

- Failure of fusion of medial nasal prominence & maxillary prominence - Failure of palatal shelves to meet in midline

Question 44

Describe the development of the following structures in the ear: - External auditory meatus - Middle ear cavity - Ossicles - Auricles

Answer 44

- **External auditory meatus** develops from the 1st Ph cleft - **Middle ear cavity** develops from 1st pharyngeal pouch - **Ossicles** develop from cartilages of 1st and 2nd arches respectively - **Auricles** develop from proliferation within the Ph Arches 1&2

Question 45

Explain how the ears are positioned

Answer 45

- Initially, external ears develop in the neck - As the mandible grows, the ears ascend to the side of the head to lie in line with the eyes

Question 46

Explain the effect of alcohol on embryological development

Answer 46

- The facial skeleton is derived from **neural crest cells** in the Ph arches - Neural crest migration as well as development of the brain are known to be **extremely sensitive to alcohol**

Question 47

What is the incidence of Foetal Alcohol Syndrome?

Answer 47

Incidence of FAS = 1 / 100 births

Question 48

Describe the effects of Foetal Alcohol Syndrome on the development of the face:

Answer 48

Question 49

What is ARND?

Answer 49

Alcohol-related neurodevelopmental delay