Embryology

Question 1

What are the layers of the embryo?

Answer 1

• Ectoderm = outer layer
• Mesoderm = middle layer
• Endoderm = inner layer

Question 2

What are pharyngeal arches composed of?
How many pharyngeal arches do we have?
Which one gives rise to the maxillary and mandible?

Answer 2

• Pharyngeal arches are composed of mesenchymal tissue
• We have 6 pharyngeal arches, but by week 4 the 5th one regresses, so it’s numbered like: 1, 2, 3, 4 and 6
• Pharyngeal arch 1

Question 3

For pharyngeal arch 1, list:
Nerve:
Nerve function:
Muscle:

Answer 3

• Trigeminal nerve
• 3 divisions – Principal sensory to the face skin and lining of mouth and nose
• Muscle: mastication

Question 4

For pharyngeal arch 2 list:
Nerve:
Nerve function:
Muscle:

Answer 4

• Facial nerve
• Taste (anterior 2/3 of tongue)
• Muscle: facial expression

Question 5

For pharyngeal arch 3, list:
Nerve:
Nerve function:
Muscle:

Answer 5

• Glossopharyngeal
• Taste (posterior 1/3 of tongue)
• Muscle: Motor innervation of stlyopharyngeal

Question 6

For pharyngeal arch 4 and 6, list:
Nerve:
Nerve function:
Muscle:

Answer 6

• Vagus

* Muscle: Motor innervation of pharyngeal constrictors and intrinsic muscles of the larynx

Question 7

State the bones that come from pharyngeal arch 1

Answer 7

Maxillary prominence
• Maxilla
• Zygomatic
• Temporal

Mandibular prominence
• Mandible
• Middle and external ear
• External acoustic meatus

Question 8

State the bones that come from pharyngeal arch 2

Answer 8

• Middle ear
• Styloid Process (temporal bone)
• Styloid ligament
• Lesser horn of hyoid bone

Question 9

State the bones that come from pharyngeal arch 3

Answer 9

• Greater horn and body of the hyoid bone

Question 10

State the bones that come from pharyngeal arch 4 and 6

Answer 10

• Thyroid cartilage

* Cartilage of larynx