Head and Neck Embryology

Question 1

What does the neck form from?

Answer 1

Branchial/pharyngeal arches

Question 2

What does the face form from?

Answer 2

5 mesenchymal processes / prominences

Question 3

Where does the skull develop from?

Answer 3

Mesenchyme in the head region of developing embryo

Question 4

What is mesenchyme?

Answer 4

Mesenchyme is embryonic connective tissue

Question 5

What is the development of the blastula?

Answer 5

Forms bilaminar disk - forms trilaminar disk.

Trilaminar disk contains amniotic cavity dorsally (ectoderm) and yolk sak ventrally (endoderm side)

Question 6

What leads to axis formation of the embryo?

Answer 6

Notochord formation

Question 7

What does the neural tube form from?

Answer 7

Forms from the ectoderm in the midline - forms - brain and spinal cord

Question 8

What does the neural crest form from?

Answer 8

Some cells at the crest of the neural fold separate to form the neural crest cells

(neural crest is seen here as the green)

Question 9

What happens to the neural crest cells?

Answer 9

They migrate and give rise to a wide variety of structures. The neural crest cells in the head and neck region mix with the mesoderm.

The neural crest cells give rise to a wide variety of structures - migrate for example dorsal root ganglia, sympathetic chain and autonomic plexus

Question 10

Where do somites arise from?

Answer 10

Paraxial mesoderm

Question 11

What do somites form?

Answer 11

Form structures like the axial skeleton and the muscles

Question 12

How many somites develop in humans?

Answer 12

33 in total

Question 13

What are pharyngeal branches?

Answer 13

Series of arches which develop around the future mouth and pharynx.

They support the primitive pharynx

Face and neck develop from the

Question 14

What embryolgical tissue makes up the branchial arches?

Answer 14

Ectoderm lines the outside and forms celfts between the arches

Mesoderm in the middle - cartilage nad muscle

Endoderm on the inside - forms pouches in between arches

Question 15

What are the nerves of the branchial arches?

Answer 15

1st arch - mandibular branch of trigeminal

2nd - arch facial nerve

3rd - arch glossopharyngeal n.

4th - arch superior laryngeal branch of vagus

(no 5th arch)

6th - arch recurrent laryngeal branch of vagus

Question 16

What are the muscles of the face innervated by?

Answer 16

Facial nerve

Question 17

If the facial nerve supplies muscles of the face, which branchial arch did they arise from?

Answer 17

From the 2nd arch

Question 18

What innervates the digastric muscle?

Answer 18

Anterior belly - mandibular division of the trigeminal nerve

Poesterior belly - facial nerve

Question 19

What cartilages form from the 1st branchial arch?

Answer 19

Meckels cartilage

Maleus

Incus

Question 20

What cartilages form from the 2nd branchial arch?

Answer 20

Stapes

Styloid process

Stylohyoid ligament

Question 21

What cartilage forms from the third branchial arch?

Answer 21

Greater horn of the hyoid bone

Question 22

What cartilage forms from the 4th branchial arch?

Answer 22

Thyroid cartilage

Question 23

What cartilage forms from the 6th branchial arch?

Answer 23

Cricoid cartilage

Question 24

What are pther important structures developing from the branchial arches?

Answer 24

• Tongue
• Thyroid gland
• Parathyroid gland
• Part of the pituitary gland

Question 25

What are the 5 prominences that the face develops from?

Answer 25

The frontonasal process Two maxillary processes Two mandibular processes

Question 26

Where does the frontonasal process come from?

Answer 26

From mesenchyme superior to future mouth

Question 27

Where do themaxillary processes come from?

Answer 27

From maxillary part of first branchial arch mesenchyme

Question 28

Where do the mandibular processes come from?

Answer 28

1st arch mesoderm

Question 29

What is the activity of the 2 mandibular processes?

Answer 29

They fuse in the midline

Question 30

How is the nasal pit formed?

Answer 30

Ectodermal thickening (nasal placode) pushes inwards to form the nasal pit

Question 31

How is the philtrum formed?

Answer 31

The medial nasal process further grows downwards and laterally

Question 32

Which colour in the picture represents the philtrum?

Answer 32

Green portion just below the nose

Question 33

What are the stages of development of the palate?

Answer 33

Stage 1: Philtrum forms by downward growth of the medial nasal process. This is known as the primary palate. Stage 2: 2 palantine shelves grow inwards from the maxillary processes Stage 3: Palantine shelves meet in the midline to form the secondary plate Oral and nasal cavity are now complete.

Question 34

What are the three bony regions of the head?

Answer 34

Cranial vault Base of the skull Viscerocranium

Question 35

What bones form the cranial vault and how are they formed?

Answer 35

Flat bones - formed by membranous ossification calvaria

Question 36

What bones form the base of the skull and how are they formed?

Answer 36

Irregular bones - endochondral ossification

Question 37

How are the bones of the viscerocranium formed?

Answer 37

Partly from branchial arches, and partly from sensory (special sense) capsules

Question 38

Where does the mesenchyme aris from that is involve in skull vault ossification?

Answer 38

Mesenchyme is derived from the mesoderm and lies above the surface of developing brain - ossifies directly (membranous ossification)

Question 39

Why are sutures soft in the skull vault?

Answer 39

Allows deformation during passage through birth canal

Question 40

How many fontanelle are of clinical significance?

Answer 40

6

Question 41

What are fontanelle?

Answer 41

A space between the bones of the skull in an infant or fetus, where ossification is not complete and the sutures not fully formed. The main one is between the frontal and parietal bones.

Question 42

Where does the mesenchyme arise from that forms the base of the skull?

Answer 42

It is found around the notochord and is derived predominantly from neural crest cells

Question 43

How are the bones of the base of the skull formed?

Answer 43

Preform in cartilage Later they ossify

Question 44

Where are sensory capsules formed?

Answer 44

Derived from mesoderm of somites in head and neck region

Question 45

What do sensory capsules form?

Answer 45

Preform in cartilage and ossify to form bones around the sense organs ## Footnote nose, eye and ear They form partly base of skull, partly viscerocranium