Embryology of Cranial Nerves

Question 1

5 paired pharyngeal arches are developed in the 4th week. What are they?

Answer 1

1st, 2nd, 3rd, 4th, and 6th

The 5th rapidly regresses and the 6th is not visible externally

Question 2

Where is the oral cavity formed on the embryo?

Answer 2

Between the frontonasal prominence and the 1st pharyngeal arch

Question 3

What are pharyngeal clefts and pouches?

Answer 3

Each pharyngeal arch is separated by a cleft externally and opposing pouches internally

Question 4

What characterises pharyngeal arches?

Answer 4

1. Skeletal components
2. Cranial nerves (cranial placodes)
3. Neural crest cells
4. Muscle cells
5. Vessels

Question 5

What are the characteristics of the frontonasal prominence?

Answer 5

1. Consists of a medial and lateral nasal prominence
2. Contributes to the development of the nose, upper lip, anterior maxilla, and palate
3. Failure to fuse can form a cleft lip or midline cleft

Question 6

What are the skeletal developments of the 1st pharyngeal arch?

Answer 6

1. Maxilla
2. Mechel’s cartilage
3. Zygoma
4. Temporal bone
5. Incus and malleus of middle ear

Question 7

What are the muscular developments of the 1st pharyngeal arch?

Answer 7

1. Muscles of mastication
2. Mylohyoid
3. Ant. belly of digastric
4. Tensor palati and tensor tympani

Question 8

What are the nerve and artery developments of the 1st pharyngeal arch?

Answer 8

1. Trigeminal nerve (CN V2 + V3)
2. Maxillary artery
3. External carotid artery

Question 9

What are the skeletal developments of the 2nd pharyngeal arch?

Answer 9

1. Reichert’s cartilage
2. Lesser horn of hyoid bone
3. Stapes of middle ear
4. Styloid process
5. Stylohyoid ligament

Question 10

What are the muscular developments of the 2nd pharyngeal arch?

Answer 10

1. Muscles of facial expression
2. Stapedius
3. Stylohyoid
4. Post. belly of digastric
5. Auricular muscles

Question 11

What is the nerve and vessel development from the 2nd pharyngeal arch?

Answer 11

1. Facial nerve (CN 7)
2. Stapedial artery

Question 12

What are the skeletal and muscular developments from the 3rd pharyngeal arch?

Answer 12

Skeletal = Greater horn + body of hyoid bone

Muscles = Stylopharyngeus

Question 13

What is the nerve and vessel development from the 3rd pharyngeal arch?

Answer 13

1. Glossopharyngeal nerve (CN 9)
2. Common and internal carotid arteries

Question 14

What are the skeletal developments of the pharyngeal arch?

Answer 14

1. Thyroid cartilage of larynx
2. Epiglottic cartilage

Question 15

What are the muscular ecvelopments of the pharyngeal arches?

Answer 15

1. Cricothyroid muscle
2. Muscles of soft palate

Question 16

What are the nerve developments of the 4th pharyngeal arches?

Answer 16

The vagus nerve (CN 10)

Question 17

What are the skeletal and muscular developments of the pharyngeal arch?

Answer 17

Skeletal = Remaining laryngeal cartilages

Muscles = Intrinsic muscles of the larynx

Question 18

What are the nerve developments of the 6th pharyngeal arch?

Answer 18

Recurrent laryngeal nerve (branch of CN 10)