Development of the head and neck part 1

Question 1

Features of the 4 week old embryo

Answer 1

No face yet
Head and neck take up almost 50% of body
Follows segmental pattern
Each segment contains structures from each system

Question 2

5 parts of each of the pharyngeal arches

Answer 2

Ectoderm
Cranial nerve
Cartilage bar
Artery
Endoderm

Question 3

What does the cartilage bar have and what does it do?

Answer 3

Associated muscles
Supports the arch (mesodermal derived)

Question 4

Cranial nerve - what does each one do in each arch?

Answer 4

Each arch has own cranial nerve
Motor innervation to muscles associated with that arch

Question 5

Artery supply to arch origin

Answer 5

Mesoderm - one of the aortic arches

Question 6

Ectoderm purpose

Answer 6

Covers superficial surface of arch - will become skin and nerve tissue

Question 6

Ectoderm purpose

Answer 6

Covers superficial surface of arch - will become skin and nerve tissue

Question 7

Endoderm purpose

Answer 7

Covers deep aspect of arch, inner lining

Question 8

What nerve is associated with arch 1?

Answer 8

Trigeminal

Question 9

Which nerve is associated with arch 2?

Answer 9

Facial

Question 10

Which nerve is associated with arch 4 and 6?

Answer 10

Vagus

Question 10

Which nerve is associated with arch 3?

Answer 10

Glossopharyngeal

Question 11

How many pharyngeal arches are there?

Answer 11

5 - but numbered 1,2,3,4 and 6 (no 5th arch in humans)

(aortic arch which supplies them corresponds to arch number)

Question 12

Muscles within arch 1

Answer 12

Muscles of mastication (supplied by mandibular portion of trigeminal nerve)

Question 13

Skeletal elements of arch 1

Answer 13

Mandible
Malleus
Incus

Question 14

Muscles associated with arch 2

Answer 14

Muscles of facial expression (supplied by facial nerve)

Question 15

Skeletal elements associated with arch 2

Answer 15

Stapes (middle ear bone that bangs on cochlea)
Superior hyoid part

Question 16

Muscles associated with arch 3

Answer 16

Stylopharyngeus

Question 17

Skeletal elements associated with arch 3

Answer 17

Inferior hyoid

Question 18

Muscles associated with arch 4 and 6

Answer 18

Pharyngeal and laryngeal muscles

Question 19

Skeletal elements associated with 4th and 6th arch

Answer 19

Laryngeal cartilage

Question 20

What is formed by the pharyngeal arches?

Answer 20

Pharyngeal cleft and pouches

Question 21

What is a pharyngeal cleft?

Answer 21

Invagination of ectoderm (pit within ectoderm, visible on outer surface)

Question 22

What is a pharyngeal pouch?

Answer 22

Evagination of endoderm - formed by inner layer

Question 23

What does the first cleft become?

Answer 23

Almost merges with 1st pharyngeal pouch, forms external acoustic meatus (tympanic membrane between)

Question 24

What does first pouch become?

Answer 24

Eustachian tube (called tubotympanic recess in embryo)

Question 25

What does the eustachian tube do?

Answer 25

Connects pharynx to middle ear

Question 26

What happens to the rest of the pharyngeal clefts?

Answer 26

Disappear

Question 27

What does the 2nd pharyngeal pouch become?

Answer 27

Palatine tonsil

Question 28

What does the 3rd pharyngeal pouch become?

Answer 28

Thymus and parathyroid III

Question 29

What does 4th pharyngeal pouch become?

Answer 29

Parathyroid IV

Question 30

What usually happens to all the clefts? (apart from 1st)

Answer 30

2nd pharyngeal arch descends over the clefts usually and closes them off

Question 31

What can occur of the descent of the 2nd arch does not fully close clefts off?

Answer 31

Can form branchial cysts, sinuses and fistulas

(branchial means pharyngeal)

Question 32

How does a branchial cyst form?

Answer 32

2nd arch descends and covers cleft but there is some inner cleft left and not fully closed off.

But there is no communication with other structures - enclosed space filled with fluid

Question 33

How does branchial sinus form?

Answer 33

2nd arch does not cover over cleft - cervical sinus remnant

Communication with skin and outside environment

Question 34

How does branchial fistula form?

Answer 34

2nd arch does not cover cleft
Cervical sinus remnant extends all the way to endoderm
Connection of skin with pharynx

Question 35

Why are branchial cysts, sinuses and fistulae almost always anterior to SCM?

Answer 35

SCM in embryo is posterior to the clefts that the 2nd arch descends down and covers