Branchial Arches

Question 1

What are branchial sinuses?

Answer 1

Openings along anterior border of sternomastoid due to failure of 2nd pharyngeal groove and cervical sinus to obliterate

Question 2

What is the terminal fate of the posterior branchial arches?

Answer 2

Arch 2 enlarges and grows over the posterior arches, forming a sinus (cervical sinus) that typically goes away by week 7

Question 3

What nerve(s) derive from branchial arch I?

Answer 3

Trigeminal (V)

branchial arch I has a maxillary and mandibular component and the ophthalmic component is a pretrematic branch

Question 4

What is Pierre-Robin Syndrome?

Answer 4

Mandibular underdevelopment + cleft palate + defects of eyes and ear

Question 5

What arteries derive from branchial arch I?

Answer 5

Part of maxillary artery

Question 6

What muscles form from branchial arch IV/VI?

Answer 6

Levator veli palatini

Pharyngeal constrictors

Intrinsic laryngeal muscles

Cricothyroid

Esophageal striated muscles

Question 7

What is the terminal structure that ectoderm forms?

Answer 7

Epidermis and sensory neurons of the epibranchial ganglia

Question 8

What structures form from the floor of branchial arch II?

Answer 8

Foramen cecum, thyroid gland

Question 9

What cranial nerve forms from branchial arch III?

Answer 9

Glossopharyngeal (IX) nerve

pretrematic branch: tympanic

Question 10

What structure forms from the groove/cleft of branchial arch I?

Answer 10

External auditory meatus

Question 11

What structure forms from the pouch of branchial arch I?

Answer 11

Middle ear chamber + eustachian tube

Question 12

What cartilaginous bones form from branchial arch II rods?

Answer 12

Stapes, styloid process, lesser horn of hyoid and upper part of the body

Question 13

What cartilaginous bones derive from arch rods of branchial arch I?

Answer 13

Malleus, incus

Question 14

What arteries are associated with branchial arch III?

Answer 14

Internal carotid

Question 15

What ligaments derive from arch rods of branchial arch I?

Answer 15

Anterior ligament of the malleus, sphenomandibular ligament

Question 16

What muscles derive from branchial arch I?

Answer 16

Muscles of mastication

anterior belly of digastric, myohyoid, tensor veli palatini, tensor tympani

Question 17

What cartilaginous bones form from branchial arch IV/VI rods?

Answer 17

Thyroid, cricoid, arytenoid cartilages

Corniculate, cuneiform cartilages

Question 18

What arteries form from branchial arch IV/VI?

Answer 18

Right subclavian, left aorta, ductus arteriosus

Question 19

What are branchial cysts?

Answer 19

Spherical or elongate cysts that are (usually) remnants of the 2nd pharyngeal groove and develop along the anterior border of the sternomastoid muscle

Question 20

What ligaments form from branchial arch II rods?

Answer 20

Stylohyoid ligament

Question 21

What muscles derive from branchial arch II?

Answer 21

Muscles of facial expression

posterior belly of digastric, stylohyoid, stapedius, auricular muscles

Question 22

What is the terminal structure that mesoderm forms?

Answer 22

Musculature and endothelial cells

Question 23

What is a pouch transformation anomaly?

Answer 23

Failure of 3rd and 4th arch pouches to differentiate into thymus and parathyroid glands (ex. DiGeorge Syndrome)

Question 24

What is first (mandibular) arch syndrome?

Answer 24

A syndrome that leads to various malformations in mandible, palate, ears that results from insufficient migration of neural crest cells into the 1st arch around week 4

Question 25

What cranial nerves are associated with branchial arch IV/VI?

Answer 25

Vagus nerve (superior laryngeal and recurrent laryngeal)

Question 26

What are the external features of branchial arch 1?

Answer 26

Maxilla, mandible, pinna of ear

Question 27

What structures form from the puch of branchial arch III?

Answer 27

Tymus, inferior parathyroid

Question 28

What membrane forms from branchial arch I?

Answer 28

Tympanic membrane

Question 29

What structure forms from the floor of branchial arch I?

Answer 29

Distal tongue buds

Question 30

What is the importance of neural crest cell migration?

Answer 30

Wk 4 - neural crest cells migrate into developping arches and form cartilaginous rods that develop into the skeleton and connective tissue of much of the face

Question 31

What structure forms from the pouch of branchial arch II?

Answer 31

Palatine tonsil

Question 32

What structures form from the floor of branchial arch III?

Answer 32

Hypobranchial eminence

Question 33

What arteries form from branchial arch II?

Answer 33

Stapedial (degenerates before birth)

Question 34

What is the terminal structure that endoderm forms?

Answer 34

Epithelial lining of the pharynx, forming taste buds + thyroid + parathyroid + thymus

Question 35

What cartilaginous bones are formed from branchial arch III rods?

Answer 35

Greater horn of hyoid and lower part of body

Question 36

What structures form from the pouch of branchial arch IV/VI?

Answer 36

Superior parathyroid, postbranchial body

Question 37

What are branchial fistulas?

Answer 37

Canal opening internally into tonsillar sinus and externally onto side of neck resulting from persistence of 2nd pharyngeal groove and puch

Question 38

What structures form from the floor of branchial arch IV/VI?

Answer 38

Hypobranchial eminence

Question 39

What external features form from branchial arch II?

Answer 39

Pinna of ear, side of neck

Question 40

What are branchial vestiges?

Answer 40

Cartilaginous or bony remnants of branchial arch cartilages which do not fully transform/disappear ## Footnote *typically anterior to inferior third of sternocleidomastoid muscle*

Question 41

What is treacher-collins syndrome?

Answer 41

Zygomatic underdevelopment + downward slanting palpebral fissures + defects of lower eyelids + deformed external ears + abnormalities of middle and internal ears

Question 42

What is the terminal structure that neural crest ectomesenchyme forms?

Answer 42

Skeletal and connective tissues of the arches

Question 43

What is the basic structure of the branchial arches?

Answer 43

Externally lined with ectoderm, internally lined with endoderm Arches separated by grooves externally and internally by pouches Each arch has a cartilaginous supportive rod, musculature, blood supply, and a nerve

Question 44

What muscles form from branchial arch III?

Answer 44

Stylopharyngeus

Question 45

What cranial nerve is associated with branchial arch II?

Answer 45

Facial nerve (VII) ## Footnote *pretrematic branch = chorda tympani*

Question 46

What bones derive from the migrated ectomesenchyme of branchial arch I?

Answer 46

Mandible, maxilla, zygomatic, palatine, pterygoid plates of sphenoid, squamous and tympanic temporal