Embryological Development (pharyngeal Arches)

Question 1

Describe the structure of a pharyngeal arch in a transverse/cross sectional image:

Answer 1

Ectoderm lines the outside
Endoderm lines the inside

Cartilage bar in the core of the arch (between ectoderm and endoderm)

Cranial nerve coming from the neural tube

Question 2

Go to the last slide of the Embryological development and label the cross sectional image of the pharyngeal arch:

Answer 2

1 = endoderm
2 = ectoderm
3 = cartilage bar
4 = neural tube
5 = cranial nerve
6 = artery

Question 3

What is derived from the ectoderm in the pharyngeal arch?

Answer 3

Skin overlying head and neck
Glands
GI
Resp
Covers superficial surface of arch

Question 4

What is derived from the endoderm of the pharyngeal arch?

Answer 4

Epithelial lining of the GI and resp (pharynx)
Endocrine glands
Covering deeep aspect of arch

Question 5

What is the function of the cartilage bar in the pharyngeal arch?

Answer 5

Supports the arch

Has muscles associated with it

Question 6

What embryological layer is the cartilage bar of the pharyngeal arch derived from?

Answer 6

Mesoderm

Question 7

Describe the general rule for cranial nerve supply and arterial supply to the pharyngeal arches:

Answer 7

Each arch has a different cranial nerve and branch of the aortic arch supplying it

Question 8

What muscles does the cranial nerve in the pharyngeal arch supply?

Answer 8

The muscles associated with the cartilage bar

Question 9

How many pharyngeal arches are there?

Answer 9

5

Question 10

How are the pharyngeal arches numbered?

Answer 10

Ordered from rostral to caudal
Arches, I, II, III, IV and VI (no V)

Question 11

What nerve and branch of the aorta supplies the 1st pharyngeal arch?

Answer 11

Trigeminal nerve (V)
Aortic arch I

Question 12

What muscles are associated with/derived from the cartilage bar in pharyngeal arch 1?

What skeletal elements are derived from pharyngeal arch 1?

Answer 12

Muscles of mastication:
-medial + lateral pterygoids
-Temporalis
-masseter

Mandible
structures of middle ear (malleus and incus)

Question 13

What nerve and branch of the aorta supplies the 2nd pharyngeal arch?

Answer 13

Facial nerve (VII)

2nd aortic arch

Question 14

What muscles are associated with/derived from the cartilage bar in pharyngeal arch 2?

What skeletal elements are derived from pharyngeal arch 2?

Answer 14

Muscles of facial expression:
-occipitofrontalis
-Orbicularis oculi
-orbicularis oris
-Buccinator
-Zygomaticus major

Stapes (middle ear bone) + superior part of hyoid

Question 15

What muscle attaches to stapes pulling on it?

Answer 15

Stapedis

Question 16

Damage to what nerve can lead to hearing problems and why?

Answer 16

Facial nerve (VII)

Muscles like stapedis supplied by it so if it gets damage doesn’t pull on stapes leading to hearing problems

Question 17

What nerve and branch of the aorta supplies the 3rd pharyngeal arch?

Answer 17

Glossopharyngeal (IX)

3rd aortic arch

Question 18

What muscles are associated with/derived from the cartilage bar in pharyngeal arch 3?

What skeletal elements are derived from pharyngeal arch 3?

Answer 18

Stylopharyngeus

Inferior part of hyoid

Question 19

What nerve and branch of the aorta supplies the 4th and 6th pharyngeal arch?

Answer 19

Vagus nerve (X) supplies both the 4th and 6th pharyngeal arch

Aortic arch 4+6 respectively

Question 20

What muscles are associated with/derived from the cartilage bar in pharyngeal arch 4+6?

What skeletal elements are derived from pharyngeal arch 4+6?

Answer 20

Pharyngeal and laryngeal muscles

Laryngeal cartilages

Question 21

What is a pharyngeal cleft?

Answer 21

Invagination in the ectoderm of the pharyngeal arch
(Invagination on the outside)

Question 22

What is a pharyngeal pouch?

Answer 22

Invagination of the endoderm around the pharyngeal arch

(Invagination on the side)

Question 23

Which one is superficial and which one is deep, the Pharyngeal cleft or the pharyngeal pouch?

Answer 23

Pharyngeal cleft = superficial

Pharyngeal pouch = deep

Question 24

What develops from the First pharyngeal pouch+cleft?

Answer 24

Ear

Question 25

What develops from the Second pharyngeal pouch+cleft?

Answer 25

Palatine tonsils

Question 26

What develops from the third and forth pharyngeal pouch+cleft?

Answer 26

Thymus gland
Parathyroids

Question 27

What is formed when the first pharyngeal pouch and the first pharyngeal cleft come into contact?

Answer 27

Thin membrane called Tympanic membrane

Question 28

What structure does the first pharyngeal pouch form?

Answer 28

Eustachian tube

Question 29

What structure does the first pharyngeal cleft form?

Answer 29

External acoustic meatus

Question 30

What structures does the Eustachian tube connect?

Answer 30

Ear with the pharynx

Question 31

What is significant about the growth of the second pharyngeal arch?

Answer 31

It grows downwards destroying the clefts from the 2nd pharyngeal cleft onwards

Question 32

What are the 3 types of disorders that can form as a result of the incorrect obliteration of the pharyngeal clefts by the second pharyngeal arch’s downward growth?

Answer 32

Branchial cysts
Branchial sinuses
Branchial fistulas

Question 33

What is a Branchial cyst?

Answer 33

An enclosed cyst filled with fluid

(Growth of second pharyngeal arch left an enclosed space)

Question 34

Where is the lump located with a Branchial cyst?

Answer 34

In the anterior triangle anterior to Sternocleidomastoid

Question 35

What is a Branchial sinus?

Answer 35

When the space left by the incomplete obliteration of the pharyngeal clefts are open to the skin (hole in skin)

Question 36

What is a Branchial fistula?

Answer 36

When the pharyngeal cleft that has failed to obliterate connects with the pharynx

Its an abnormal connection with the ectoderm and the endoderm