Pharyngeal Arches

Question 1

What 4 major tissue types do each arch develop into?

Answer 1

Cranial nerve
Cartilage (which become bones)
Muscle
Blood vessels (focus on arteries)

Question 2

What CN, muscles, cartilages and vessels come from Pharyngeal Arch 1?

Answer 2

CNV: trigeminal (maxillary and mandibular branches)
Cartilage: maxilla, zygoma and mandible, malleus and incus
Muscles: of mastication - masseter, pterygoids and temporalis
Artery: maxillary artery (remnant of aortic arch 1)

Question 3

What CN, muscles, cartilages and vessels come from Pharyngeal Arch 2?

Answer 3

CNVII: facial (supplies muscles of facial expression)
Cartilage: stapes; styloid process & superior portion of hyoid (Cornu / lesser horn)
Muscles: of facial expression (& stapedius)
Artery: stapedial artery (remnant of aortic arch 2)

Question 4

What CN, muscles, cartilages and vessels come from Pharyngeal Arch 3?

Answer 4

CNIX: Glossopharyngeal (supplies post. Tongue & pharynx; pharyngeal plexus)
Cartilage: inferior part of hyoid
Muscles: stylopharyngeus (only one not vagus)
Artery: common, internal and external carotids (aortic arch 3)

Question 5

What CN, muscles, cartilages and vessels come from Pharyngeal Arch 4?

Answer 5

CNX: vagus (superior laryngeal branch)
Cartilage: thyroid & cricoid cartilages
Muscles: constrictors of the pharynx & cricothyroid (only m. Of larynx innvervated by superior laryngeal branch)
Artery: Right = subclavian artery Left = aortic arch (aortic arch 4)

Question 6

What CN, muscles, cartilages and vessels come from Pharyngeal Arch 6?

Answer 6

CNX: vagus (recurrent laryngeal branches)
Cartilage: arytenoids (cuniform and corniculate)
Muscles: intrinsic muscles of larynx except cricothyroid
Artery: aortic arch 6 (pulmonary arteries) Right dorsal aorta which disappears, Left = ductus arteriosus (ligamentum arteriosus)

Question 7

Describe the different routes the left and right recurrent laryngeal nerves take and why?

Answer 7

Due to the ductus arteriosum (later ligamentum) remaining the LEFT recurrent laryngeal descends LOWER into thorax than the right, looping around the aorta before it ascends to the larynx past the trachea.
The RIGHT loops under the RIGHT SUBCLAVIAN artery and ascends back up past trachea to the larynx

Question 8

What are clefts and what are pouches (referring to pharyngeal arches)?

Answer 8

Clefts - external “grooves” of pharyngeal arches, derived from ectoderm
Pouches - internal “pouches” within the ectoderm, derived from endoderm

Question 9

Which cleft / pouch / arches the important ones which regards to formation of a crucial anatomical feature of the head and what is that feature?

Answer 9

Cleft 1 (between arches and pouches 1&2)
Forms the external acoustic meatus and external side of tympanic membrane whilst the pouches (1&2) form the internal side of the tympanic membrane

Question 10

What glands do pharyngeal pouches 3&4 form?

Answer 10

Parathyroids
Thyroid (c cells - secrete calcitonin)
Thymus

Question 11

Problems with which cells in embryologic development are likely to cause conditions such as: Treacher Collins Syndrome, Pierre Robin Syndrome and DiGeorge Syndrome?

Answer 11

Neural Crest Cells (which migrate to help form the pharyngeal arches in early embryonic development)

Question 12

Between which weeks of gestational development do pharyngeal arches appear and then form their respective CNs, muscles, cartilages and vessels?

Answer 12

Weeks 4-7

Question 13

How many ‘functional’ pharyngeal arches are there?

Answer 13

5 (1,2,3,4&6)