Development

Question 1

HN development: what does mesoderm give rise to

what does neural crest?

Answer 1

Mesoderm - craniofacial muscles

• neurocranium
• laryngeal cartilages

Neural crest -viscerocranium
tendons 
stroma
bones of the face 
dentin

Question 2

HN development: What are the derivatives of ectoderm, mesenchyme (mesoderm + neural crest), and endoderm?

Answer 2

Ectoderm:
Epidermis is from surface ectoderm.

Forebrain and spinal cord is from neural ectoderm.

Ectoderm forms wedges between the arches known as pharyngeal clefts (1,2,3,4)

Mesenchyme:
-5 pharyngeal arches (1,2,3,4,6)

Endoderm: pharynx
-inner surface of the pharyngeal arches and wedges and these are the pharyngeal pouches (1,2,3,4)

Question 3

Each pharyngeal arch has a different cranial nerve and skeletal muscle group. What is in arches 1,2,3,4,6?

Answer 3

1. Trigeminal (V)
   - muscles of mastication
   - anterior digastric
   - tensors (all tensors = mandibular)
   - mylohyoid
2. Facial (VII)
   - muscles of facial expression
   - posterior digastric
   - stapedius
   - stylohyoid
3. Glossopharyngeal (IX)
   - stylopharyngeus
4. Vagus (X), superior laryngeal
   - soft palate muscles
   - pharyngeal muscles
   - cricothyroid
5. Vagus, recurrent laryngeal
   - intrinsic laryngeal muscles, esophageal muscles

Question 4

What are the connective tissue and aortic arch in each of the pharyngeal arches?

Answer 4

1. Malleus, inus, mandible, (I’d say memorize the other arches and anything else is arch 1)

blood- maxillary

2. Stapes, styloid process, hyoid lesser horn, hyoid-upper body

blood - stapedial

3. Hyoid greater horn, hyoid -lower body

blood- part of internal carotid

4 + 6 laryngeal cartilages

• —–2+3—make a hyoid bone —-
• —–1+2 —–make the full ear apparatus

Question 5

Describe development of the tongue

Answer 5

Its a combination of arches 1,2,3 and 4.

Therefore taking contributions from V3, VII, IX, X.

Anterior 2/3 of tongue: general sensation is V3
-special sensory is facial

Posterior 2/3 of tongue: general sensory and special sensory is glossopharyngeal

Hypoglossal nerve: myoblasts from occipital somitomeres (paraxial mesoderm) migrate to develop tongue mesenchyme which brings the hypoglossal nerve for somitic motor innervation.

Question 6

What is ankyloglossia?

What is bifid tongue?

Answer 6

Ankyloglossia is when the tongue is tethered to the floor of the mouth.

Bifid tongue is a result of incomplete fusion of the lateral swellings.

Question 7

Face development:

what do each of these become?

1 frontonasal prominence

Nasolacrimal groove

Nasal placode - pit

2 maxillary prominences

2 mandibular prominences

Answer 7

Frontonasal prominence (intermaxillary segment): forehead, nose, nose bridge, *philtrum of upper lip, *primary palate (hard)

Nasolacrimal groove - nasolacrimal duct

Nasal placode - pit - nasal cavity (epithelium)

Maxillary prominences - *palatine shelves, cheeks, lateral upper lip, secondary palate (soft), most teeth

Mandibular prominences - lower lip, jaw

Question 8

Describe how a definitive palate is formed fused to the nasal septum with the movement of the tongue?

Answer 8

At first, the tongue is elevated between two palatine shelves.

Then the tongue flattens out so the palatine shelves can become horizontally oriented.

The intermaxillary segments pushes the nasal prominences together at the midline to form the primary palate.

Palatine shelves fuse in the midline to form the secondary palate.

This results in a definitive palate with an incisive foramen.

Question 9

How do each of these deformities result?

Answer 9

Cleft chin - improper fusion of the mandibular prominences

Oblique facial cleft - improper fusion of the maxillary and lateral nasal prominences

Anterior cleft deformity - incomplete fusion of the primary and secondary palates at the incisive foramen

Posterior cleft deformity - incomplete fusion of the palatine shelves at the midline.

Question 10

What do the four pharyngeal clefts become?

Answer 10

Only the first cleft becomes…

• epithelial lining of the external auditory meatus
• outer lining of the tympanic membrane

2,3,4 are overgrown by mesenchyme and form a cervical sinus which is supposed to disintegrate.

What can happen is they form lateral cervical cysts along the anterior surface fo the sternocleidomastoid.

Question 11

What are the three placodes?

Answer 11

Placodes are surface ectoderm thickenings that will give rise to special sensation

Nasal placode - olfactory epithelium for smell

Otic placode - cochlea for hearing
-vestibular apparatus for balance

Lens placode - associated eye structures for vision

Question 12

What are the derivatives of the pharyngeal pouches?

Answer 12

Pouch 1- inner lining of the tympanic membrane
-middle ear and auditory tube

Pouch 2: palatine tonsils (lymphocytes migrate in)

Pouch 3: inferior parathyroid gland
-thymus: tonsil of the thyroid

• Pouch 4: superior parathyroid gland…great
• pouch 4 also contains neural crest cells which form the parafollicar cells of the thyroid.

Question 13

What does the stomodeum of the pharyngeal ectoderm form?

Answer 13

1. Lining of the oral cavity
2. Anterior pituatary

(the posterior pituatary comes from the HYPOTHALAMUS)

Question 14

What does the second and third pharyngeal pouches form?

Answer 14

2nd pouch - palatine tonsils

3rd - inferior parathyroid gland and thymus

Question 15

What are all the components and derivative sof the 4th arch?

Answer 15

Vagus nerve - superior laryngeal branch

Artery: subclavian (right) and aortic arch (left)

Muscles: soft palate, pharyngeal muscles, cricothyroid

Connective tissue - laryngeal cartilages.

Question 16

What does the frontonasal eminence form?

Intermaxillary segment *

Answer 16

Forehead, nose, nasal septum

• philtrum of upper lip
• primary palate

Question 17

What is the cause of an oblique facial cleft?

Answer 17

Improper fusion between the maxillary and lateral nasal prominences.