Pharyngeal Arches

Question 1

What does each germ layer give rise to?

Answer 1

Ectoderm - nervous system, epidermis in skin
Mesoderm - skeleton, muscle, dermis, kidney, gonads, blood
Endoderm - gut, liver, lungs, thyroid

Question 2

What 4 different tissues give rise to the head?

Answer 2

Neural crest, mesoderm, endoderm, ectoderm

Question 3

What happens during the fourth week of embryonic development?

Answer 3

The neural folds meet superior to the neural groove and form the neural tube. Neural folds also forms the cells of the neural crest (migratory populations of cells, multipotent, give rise to certain tissues in the face&neck).

The embryo then folds along this tube. Anterior end of the neural tube rapidly expands to form the beginning of the forebrain, midbrain and hindbrand.
Continued development of somites.

Question 4

Where does the epidermis go once a neural tube has formed from a folded neural plate?

Answer 4

It sits above the neural crest and neural tube.

Question 5

What is the 4th germ layer and give some details on this?

Answer 5

The Neural Crest

The NC forms at the lateral edges of the neural plate, at the boundary with the epidermis. Crest cells delaminate from the neural tube and migrate away.

Question 6

What happens to the anterior part of the neural tube when the forebrain, midbrain and hindbrain form?

Answer 6

They expand greatly.

Question 7

What is the name of the eight bulges developed from the part of the neural tube that forms the hindbrain?

Answer 7

Rhombomeres

Question 8

What does the mesoderm do laterally to the neural tube?

Answer 8

Segments to form 7 somatomeres and fully segments caudally to form somites.

Question 9

What does migration of neural crest cells provide?

Answer 9

Embryonic connective tissue needed for craniofacial development.

Question 10

Name some vital cells that multipotent neural crest cells can divide into?

Answer 10

Odontoblasts, cartilage, dermis, schwann cells, membrane bones

Question 11

What arches do the neural crest cells migrate into?

Answer 11

Branchial (pharyngeal) arches

Question 12

Where do neural crest cells originate?

Answer 12

At dorsal neural folds

Question 13

What else do neural crest cells contribute to?

What is most likely to happen here if there is a defect?

Answer 13

Cardiac Formation
(there are cardiac neural crest cells).

Mixing of oxygenated and deoxygenated blood.

Question 14

Pharyngeal Arch:
When does it appear?
What does it consist of?
How are they separated by each other?

What are the 5 arches numbered?

Answer 14

4th and 5th weeks of development.

A bar of mesenchymal tissue, lined in outside of ectoderm and inside endoderm.

Separated by deep clefts on outside and pouches on inside.

1, 2, 3, 4, 6 (no 5th arch as this separates the arches)

Question 15

What does the first pharyngeal arch develop to?

Answer 15

The mandibular prominence.

Question 16

The development of the —- —- forms the stomatodeum?

Answer 16

Frontal prominence

Question 17

What are the 5 facial primordia and their positions?

Answer 17

1 X frontonasal process
(cranially)
2 X maxillary processes (laterally)
2 X mandibular processes (caudally)

Question 18

What is the first branchial arch?

Answer 18

The mandibular

Question 19

Which way around are the cleft and the pouches? (outside and inside)

Answer 19

Cleft - outside

Pouches - inside

Question 20

What is the basic structure of each branchial arch?

General structure of the pharyngeal arch?

Answer 20

Cartilage, nerve. artery
Extra - mesenchymal tissue and ectodermal epithelium.

Ectoderm (outside), mesenchyme (neural crest and mesoderm in middle), endoderm (inside).

Question 21

What is the difference between the primary and secondary palate?

Answer 21

Primary - portion of the alveolar ridge containing the 4 incisors.
Secondary - forms remaining hard palate and all of soft palate.

Question 22

What is the incisive foramen?

Answer 22

Funnel-shaped opening in the bone of the oral hard palate immediately behind incisor teeth where blood vessels and nerves pass.

Question 23

What does each arch have?

Why is this important in dentistry?

Answer 23

Each has separate cranial nerves.

Important for when giving local anaesthetic to a patient.

Question 24

Explain what the first arch gives rise to? Give details on this

Answer 24

Located between the stomodeum and first pharyngeal pouch (shall give rise to the two lower thirds of the face).
The maxillary and mandibular processes may be isolated, respectively in a more dorsal and in a more anterior position, located laterally and inferiorly to the stomodeum.

Question 25

What derives from the maxillary process?

Answer 25

From the maxillary process derives the …. maxilla and palate, maxillary bone, premaxillary bone, zygomatic bone, squamous part of temporal bone.

Question 26

Where is the mandibular process located and what will it form?

Answer 26

Located in the Meckels cartilage.

Forms the incus and the malleus.

Question 27

How does the mandibular bone form?

Answer 27

From ossification of the mesenchymal tissue of the Meckel’s cartilage itself.

Question 28

Masculature of the 1st arch forms what?

The nerve supply is from which cranial nerve?

Answer 28

Muscles of mastication

5

Question 29

What rises from Meckels cartilage?

Answer 29

From which mandible develops

Question 30

Give 3 points on the second arch

Answer 30

• Hyoid arch, the cartilage forms the stapes, styloid process on the base of the skull, and lesser horns and upper part of the hyoid bone.
• Muscles are the functional group of ‘muscles of facial expression’
• Nerve supply is from cranial never 7 (facial)

Question 31

What muscles do each arch (1,2,3,4,6) form?

Answer 31

1 - muscles of mastication
2 - muscles of facial expression
3 - stylopharyngeus (muscle of the head)
4 - constrictors of pharynx
6 - intrinsic muscles of larynx

Question 32

What cartilage forms from each arch?

Answer 32

1 - Meckels cartilage 
2 - Stapes, styloid process
3 - Greater horns of hyoid
4 - Cartilages of larynx 
5 - Cartilages of larynx

Question 33

Give 3 details on the third arch

Answer 33

1. Cartilage forms (greater horns and the lower part of the hyoid bone)
2. Muscle - stylopharyngeus muscle
3. Nerve supply is via cranial nerve 9 (glossopharyngeal nerve)

Question 34

Pharyngeal Cleft:
What are the clefts lined with?
Only — forms a structure in the adult.
What does the first cleft between the first and second arch forms?

Answer 34

Lined with ectoderm

One

External Auditory Tube

Question 35

First Pharyngeal Cleft:
What happens in the 3rd month?
What forms?

When are the other clefts obliterated?

Answer 35

The ectoderm at bottom of cleft between 1st and 2nd arch proliferates.
It forms solid epithelial plate of cells ‘meatal plug’.

During development.

Question 36

What is the tubotympanic recess?
What is the primitive tympanic?

What does the proximal part narrow to form?

Answer 36

The first pharyngeal pouch (forms stalk like projection).

A distal portion widens into a sac - like structure.

Forms the auditory tube.

Question 37

Give some details on the 2nd, 3rd, 4th, and 5th pouches

Answer 37

2nd - palatine tonsils
3rd - dorsal wing, inferior parathyroid gland (both loose connections to wall and thymus migrate down neck dragging the inferior parathyroid with it.
4th - superior parathyroid glands
5th - ultimobranchial body (incorporated into the thyroid. Forms the parafollicular or C-cells of the thyroid). These secrete calcitonin regulating Ca2+ levels in the blood.

Question 38

What is formed from the pharyngeal pouch 1 and pouch 2?

Superior and inferior part of pouch 3?

Superior and inferior part of pouch 4?

Answer 38

1 - auditory tube and middle ear cavity
2 - numerous infoldings that become the crypts of the palatine tonsil.

Superior = the inferior parathyroid glands. 
Inferior = forms the thymus 

Superior = superior parathyroid glands 
Inferior = 5th pharyngeal pouch

Question 39

What tip of the tongue is attached to the mandible?

Answer 39

The distal tip

Question 40

What nerves innervate each arch?

Answer 40

1st arch - cranial nerve 5
2nd arch - facial nerve 7
3rd arch - glossopharngeal 4
4th arch - vagus nerve 5

Question 41

How many mesodermal origins are there for tongue muscle origins?

Answer 41

2

Question 42

What happens during the fifth and sixth weeks of embryonic development?

Answer 42

• bilateral maxillary processes derived from first brachial arch fuse with the medial nasal process to form the upper lip, alveolus, and the primary plate.
• lateral nasal process forms the alar structures of the nose
• lower lip and jaw are formed by the mandibular process

Question 43

What happens during the development of the palatal shelves?

What happens at the same time as this?

Answer 43

The primary plate is formed by an extension of the intermaxillary process.
The secondary palate from from palatine shelves that grow medially from the maxillary prominences.

At the same time, growth of the nasal septum separates the left and right nasal chambers.
Initially, the palatine shelves grow beneath the tongue but soon move upwards to meet at the midline above the tongue (these fuse to form the nasal septum). The lower part of the palate undergoes ossification forming the hard palate. Fusion of the palatine shelves occurs 1 week earlier in male embryos.

Question 44

What is the primary palate an extension of?

Answer 44

Extension of the maxillary process.

Question 45

What is the primary causes of cleft palate?

Answer 45

The palatal shelves fail to fuse with each other, inadequate growth of the palatine shelves, failure to the shelves to elevate above the tongue, an excessively wide head, failure to fuse and secondary rupture after fusion.

Question 46

Cleft palate: The muscular defects reduce the articular motion: what 3 things are limited?
What happens when the patient opens their mouth?

Answer 46

Opening, protrusion, and lateral movements are limited.

The mandible deviates towards the affected side because of the absence of an adequate leverage.