Embryology

Question 1

How many branchial arches are there + how many branchial arches does the neck develop from

Answer 1

6

5

Question 2

What is mesenchyme

Answer 2

Embryonic connective tissue

Question 3

What 2 regions of the embryo is there no mesoderm and why is this

Answer 3

Head and tail region - to form a hole for the mouth and anus

Question 4

Which germ layer are the somites derived from + what do they help develop

Answer 4

Paraxial mesoderm

Cranial skeleton

Question 5

Where do branchial arches develop around

Answer 5

Around the future mouth and pharynx

Question 6

What week gestation do pre-branchial arches form

Answer 6

4

Question 7

What does each branchial arch contain (3)

Answer 7

A skeletal element
Artery
Nerve

Question 8

Why does the neck only develop from 5 branchial arches when there’s 6 in total

Answer 8

Arch 5 disappears

Question 9

How many mesenchymal processes does the face develop from + name them

Answer 9

5:
1 frontonasal process
2 maxillary processes
2 mandibular processes

Question 10

1st branchial arch innervated by what nerve

Answer 10

CN V3

Question 11

2nd branchial arch innervated by what nerve

Answer 11

Facial nerve

Question 12

3rd branchial arch innervated by what nerve

Answer 12

Glossopharyngeal nerve

Question 13

4th branchial arch innervated by what nerve

Answer 13

Superior laryngeal nerve (branch of vagus)

Question 14

6th branchial arch innervated by what nerve

Answer 14

Recurrent laryngeal nerve (branch of vagus)

Question 15

Cranial vault (neurocranium) formed of flat bones which is formed by what type of ossification

Answer 15

Membranous

Question 16

Base of skull formed of irregular bones which is formed by what type of ossification

Answer 16

Endochondral

Question 17

Viscerocranium (Facial skeleton) formed by what embryologically

Answer 17

Mesenchyme of branchial arches and sensory capsules

Question 18

Name a congenital facial defect

Answer 18

Cleft lip + palate

Question 19

What causes cleft lip

Answer 19

failure of fusion of the maxillary and medial nasal (frontonasal) processes (failure of formation primary palate)

Question 20

What causes cleft palate

Answer 20

failure of fusion of the palatine shelves (failure of formation of the secondary palate)

Question 21

Name a congenital abnormality of the head

Answer 21

Craniosynotosis

Question 22

What is craniosynotosis

Answer 22

Skull bones fused too early

Question 23

Which branchial arch is affected in treacher collins syndrome

Answer 23

1st branchial arch abnormality

Question 24

Some cells at the crest of the neural fold (before fully becoming a closed tube) in the ectoderm midline separate to form what kind of cells

Answer 24

Neural crest cells - mix with mesoderm in the head and neck region of embryo

Question 25

What 3 tissues make up branchial arches

Answer 25

Ectoderm Mesoderm + neural crest cells Endoderm

Question 26

What branchial arch do the maxillary processes arise from

Answer 26

1st branchial arch mesoderm

Question 27

What branchial arch do the mandibular processes arise from

Answer 27

1st branchial arch mesoderm

Question 28

What tissue do the frontonasal processes arise from

Answer 28

Mesenchyme superior to future mouth

Question 29

Describe how the face forms from the mandibular & frontonasal (medial nasal) processes (4)

Answer 29

1. The 2 mandibular processes fuse in the midline 2. Ectoderm thickens to form 2 NASAL PLACODES which push inwards (invaginates) to form NOSTRILS, thus separating the frontonasal process --> 2 LATERAL NASAL PROCESSES 3. The nasal placodes migrate downwards and fuse, forming a MEDIAL NASAL PROCESS in the midline 4. The medial nasal process further grows downwards and laterally to form a process called the PHILTRUM

Question 30

Describe the formation of the palate (3)

Answer 30

1. Medial nasal process grows downwards and forms the philtrum --> PRIMARY PALATE 2. From the maxillary processes, 2 palatine shelves grow inwards 3. The palatine shelves meet in the midline to form the SECONDARY PALATE ORAL CAVITY AND NASAL CAVITY ARE NOW SEPARATE

Question 31

Cleft lip is due to failure of fusion of what processes

Answer 31

Maxillary and medial nasal (frontonasal) processes

Question 32

Cleft palate is due to failure of fusion of what processes

Answer 32

Palatine shelves (they fuse to form the secondary palate)

Question 33

Structures arising from 1st branchial arch (4)

Answer 33

Anterior belly of digastric Muscles of mastication - Malleus + incus (of ossicle) Anterior 2/3 tongue

Question 34

Structures arising from 2nd branchial arch (4)

Answer 34

Muscles of facial expression Posterior belly of digastric Stapes Suprahyoid muscles

Question 35

Structures arising from 3rd branchial arch (3)

Answer 35

Lower hyoid bone Infrahyoid muscles Posterior 1/3 tongue

Question 36

Structures arising from 4th branchial arch (2)

Answer 36

Thyroid cartilage | Larynx

Question 37

Structures arising from 6th branchial arch (1)

Answer 37

Cricoid cartilage