Branchial Arches

Question 1

What is the pharynx and what germ layer is it derived from?

Answer 1

Region behind oral and nasal cavities

Endoderm

Question 2

How are the branchial arches formed?

Answer 2

Neural Crest cells migrate to the head and neck lateral to the rostral part of the foregut and from the arch structures

Question 3

What are branchial grooves?

Answer 3

Ectodermal lefts between adjacent arches

Question 4

What are branchial pouches?

Answer 4

Endodermal out pocketing from rostral foregut, between adjacent arches

Question 5

What four things do each branchial arch have?

Answer 5

Cartilage

Nerve

Artery

Muscle

Question 6

What are the four elements of the branchial apparatus?

Answer 6

Branchial Arch

Branchial Groove

Branchial Pouch

Branchial Membrane - site of contact of groove and pouch

Question 7

What does the first arch form?

Answer 7

Face, has maxillary and mandibular processes

Surrounds stomodeum (primitive mouth)

Question 8

What is the oropharyngeal membrane?

Answer 8

Boundary between the mouth and the pharynx

Location of Palatoglossal arch

Question 9

What is formed from the first arch?

Answer 9

Skeletal - Malleus, Incus

Ligaments - Ant. ligament of the malleus, Sphenomandibular ligament

Muscles - Branchiomotor innervation of CN V

Question 10

What is formed form the second arch?

Answer 10

Skeletal - Stapes, Styloid process, Hyoid (Lesser horn, upper half of body)

Ligaments - Stylohyoid ligament

Muscles - Branchiomotor innervation of CN VII

Question 11

What is formed from the third arch?

Answer 11

Skeletal - hyoid bone (greater horn, lower half of body))

Muscles - stylopharengeus (IX)

Question 12

What is formed from the fourth arch?

Answer 12

Skeletal - Cartilages of the larynx

Muscles - branchiomotor innervation of CN X

Question 13

What is formed from the sixth arch?

Answer 13

Muscles - Sternocleidomastoid, Trapezius (CN XI)

Question 14

What forms the external auditory meatus?

Answer 14

First branchial groove

Question 15

What forms the tympanic membrane?

Answer 15

First branchial membrane

Question 16

What does the first branchial pouch form?

Answer 16

Auditory tube and tympanic cavity

Clinical: First branchial cleft cyst - tract linked to external auditory meatus

Question 17

What does the second branchial pouch form?

Answer 17

Lining of palantine tonsils

Clinical: Second branchial cleft cyst - tract linked to tonssilar fossa

Question 18

What does the third branchial pouch form?

Answer 18

Inferior parathyroid gland, Thymus

Clinical: Third Branchial Cleft cyst - tract at thyrohyoid membrane or piriform recess

Question 19

What does the fourth branchial pouch form?

Answer 19

Superior parathyroid gland, C-cells of thyroid

Clinical: does not form

Question 20

What do branchial grooves 2-6 form?

Answer 20

Cervical sinus

Question 21

What is a branchial sinus?

Answer 21

Anomaly that results in blind pouch from pharynx

Question 22

What is a branchial fistula?

Answer 22

Anomaly

Channel, often connecting pharynx to skin of neck; usually passes anterior to sternocleidomastoid between int. and ext. carotid A.

Question 23

How does the thyroid develop?

Answer 23

Starts as median endodermal thickening on floor of pharynx

Elongates to form thyroid diverticulum; descends anterior to hyoid bone and larynx

Thyroglossal duct connects diverticulum to foramen cecum

Question 24

What is a lingual thyroid?

Answer 24

The thyroid gland does not migrate and lies within the tongue

Question 25

What are thyroglossal duct remnants?

Answer 25

Can form thyroid tissue cysts along path

Question 26

What is a pyramidal lobe?

Answer 26

In 50% of people the thyroid is atttached to hyoid by fibrous strand; no clinical problems