Arches 2

Question 1

What happens to brachial arch 5?

Answer 1

disappears very early in development

Question 2

What does pharyngeal arches consist of?

Answer 2

• Ectoderm (outside)
• Endoderm (inside except 1st arch)
• Cartilage
• Blood vessels and Nerve
• Muscle

Question 3

What happens to meckels cartilage?

Answer 3

disappears by week 20 and is replaced by bone

Question 4

describe 1st pharyngeal arch (mandibular arch)

Answer 4

• mandibular and maxillary process
• cartilage : meckel’s cartilage:
• Primitive support, largely disappears
  forms:
  2 bones:
• incus
• malleus
  2 ligaments:
• sphenomandibular
• Sphenomalleolar

Question 5

what does the 1st pharyngeal arch give rise to:

Answer 5

• Body of tongue
• muscles of mastication:
• Temporalis, masseter, pterygoids
• mylohyoid, anterior body of digastric
• Nerve: V (Trigeminal)
• Maxillary and Carotid arteries

Question 6

Describe Treacher- collins syndrome

Answer 6

• Genetic-can be a simple as a single polymorphism
• Failure of neural crest cell migration
• Facial bone hypoplasia:
  mandible and zygoma
• Ear abnormalities
• Clefts
• Dental anomalies:
• Tooth agenesis
• Enamel deformities
• Misplacement upper 6s

Question 7

describe 2nd pharyngeal arch

Answer 7

• cartilage: Reichert’s cartilage
  forms:
• stapes
• lesser horn and superior hyoid body
• styloid process, stylohyoid ligament
• muscles: facial expression and posterior belly of digastric
• thyroid gland and tonsil
• nerve: VII (facial)

Question 8

describe 3rd arch

Answer 8

forms:
- greater horn of hyoid
- inferior hyoid body
- forms root of the tongue
- stylopharyngeus muscle
- Nerve: IX - glossopharyngeal

Question 9

describe 4th arch

Answer 9

• forms thyroid cartilage
• pharynx and epiglottis
• muscles:
• pharyngeal constrictor
• soft palate
• Nerve: X (vagus) - sup.laryngeal

Question 10

describe 6th arch

Answer 10

• Cricoid + arytenoid cartilages
• Larynx
• Muscles of larynx
• Nerve: vagus X - inf.laryngeal nerve

Question 11

describe 2nd-6th clefts

Answer 11

disappear - obliterated by the proliferating 2nd arch

Question 12

How do pouches normally form?

Answer 12

between arches

Question 13

describe the 1st pouch

Answer 13

• Eustacian tube
• Middle ear cavity
• tympanic membrane
• ventral part obliterated by the tongue

Question 14

describe the 2nd pouch

Answer 14

• Tonsillar fossa
• Ventral part obliterated by the tongue

Question 15

describe the 3rd pouch

Answer 15

• Inf. parathyroid gland and thymus

Question 16

describe the 4th pouch

Answer 16

• Sup. parathyroid gland

Question 17

describe the pharyngeal membranes

Answer 17

• Appear in the floor of the pharyngeal grooves
• these membranes form where the epithelia of the grooves and pouches approach each other
• the endoderm of the pouches and ectoderm of the grooves are soon separated by mesenchyme
• only first pharyngeal membrane becomes the tympanic membrane, others obliterate

Question 18

Answer 18

Question 19

Answer 19

Question 20

Answer 20

Question 21

Answer 21

Question 22

Answer 22