Embryology (Head and Neck)

Question 1

What are the five pharyngeal arches and what CN is associated with each?

Answer 1

• Arch 1: Trigeminal (CN V)
• Arch 2: Facial (CN VII)
• Arch 3: Glossopharyngeal (IX)
• Arch 4: Vagus (X)
• Arch 6: Vagus (X)

Question 2

Cartilage of the second pharyngeal arch becomes a part of which four structures?

Answer 2

• Part of body and lesser horn of Hyoid bone
• Styloid process
• Stylohyoid ligament
• Stapes

Question 3

What are the four muscles/muscle groups that are derived from the second arch? What CN are these muscles innervated by?

Answer 3

• Stylohyoid
• Posterior belly of Digastric
• Stapedius
• Muscles of facial expression
  ALL are innervated by CN VII

Question 4

Swellings from the floor of the developing pharynx contribute to the development of what body structure?

Answer 4

Tongue

Question 5

Which two swellings come from arch 1? What is the innervation of this arch and what does this nerve contribute to later in life (hint: think nerve fiber type)

Answer 5

Lateral lingual swellings and Tuberculum impar both come from arch 1
- Arch 1: innervated by CN V so contributes to the sensation of the anterior 2/3 of tongue

Question 6

Which swelling comes from arch 2, 3 and 4? What are the innervations of these arches and what do these nerves contribute to later in life (hint: think nerve fiber type)

Answer 6

Copular comes from arches 2, 3 and 4

• Arch 2: innervated by CN VII so contributes to taste of the anterior 2/3 of tongue
• Arch 3: innervated by CN IX so contributes to both sensation and taste of posterior 1/3 of tongue
• Arch 4: innervated by CN X so contributes to both sensation and taste of posterior 1/3 of tongue

Question 7

What other swelling comes from arch 4? What is the innervation of this arch and what does this nerve contribute to later in life (hint: think nerve fiber type)

Answer 7

Epiglottal swelling comes from arch 4

- Arch 4: innervated by CN X so contributes to both sensation and taste of posterior 1/3 of tongue

Question 8

Which of the four arches is initially involved in tongue development but eventually disappears? Which arch is the swelling of this arch incorporated into?

Answer 8

Arch 2 disappears and its swelling is incorporated into Arch 1 (BUT nerve fibers from CN VII are carried with it, hence why both nerves contribute to the anterior 2/3 of the tongue)