1-Pharyngeal Arches

Question 1

Bones of the 4 & 6 arches

Answer 1

Thyroid Cricoid Arytenoid Corniculate Cuneiform cartilages of larynx

Question 2

Bones of the Second Pharyngeal Arch

Answer 2

Stapes Styloid process of temporal bone Stylohyoid ligament Lesser Horn of hyoid Upper body of hyoid

Question 3

Bones of the Third Cartilage

Answer 3

Greater Horn of hyoid Lower part of hyoid

Question 4

Bones that arise from the Mandibular Process

Answer 4

Mandible

Question 5

Bones that arise from the Maxillary Process

Answer 5

Premaxilla Maxilla Zygomatic Part of temporal bone

Question 6

Cartilage that disappears in the second arch

Answer 6

Reichert’s Cartilage

Question 7

Cause of Branchial FIstulas

Answer 7

Failure of 2nd pharyngeal cleft to overgrow the 3rd, 4th, 5th which means the sinus will not disappear *Can result in a lateral cervical cyst

Question 8

Cleft 1

Answer 8

Only cleft to produce definitive structure - gives rise to external auditory meatus

Question 9

Cleft 2

Answer 9

Grows over the third, fourth, and fifth clefts and fuses with the epicardial ridge to form the cervical cinus

Question 10

Derivation of bone in the third arch

Answer 10

Cartilage

Question 11

Derivation of bones in the second hyoid arch

Answer 11

Neural crest cells

Question 12

Derivation of structures in the 4 & 6 arches

Answer 12

Lateral plate mesoderm / mesenchyme (not Neural crest cells)

Question 13

Derivation of the bones of the first arch

Answer 13

Mesoderm and NC cells

Question 14

DiGeorge Sequence

Answer 14

3rd & 4th Pouch Malformations –> CATCH 22: Cardiac defects Abnormal face Thymic hypoplasia Cleft Palate Hypocalcemia *Also hypertelorism (widely spaced eyes), abnormal ears, immunological problems

Question 15

How can Retinoic acid induce abnormalities in high doses?

Answer 15

1) Induce reactive oxygen species (ROS) to induce cell damage or death in neural crest cells 2) Hyper-activate Hox genes leading to overabundance of Hox proteins in neural crest cells

Question 16

Innervation of the 4th & 6th Arches

Answer 16

Vagus (CN X) Specifically 4th = superior laryngeal 6th= Recurrent laryngeal

Question 17

Innervation of the first arch

Answer 17

Mandibular branch of trigeminal nerve (CN V)

Question 18

Innervation of the Second Arch

Answer 18

Facial nerve (CN VII)

Question 19

Innervation of the Third Arch

Answer 19

Glossopharyngeal (CNIX)

Question 20

Muscle of the Third Arch

Answer 20

Stylopharyngeus muscles

Question 21

Muscles of the 4 & 6 arches

Answer 21

Cricothyroid Levator Palatini Constrictors of pharynx

Question 22

Muscles of the First Pharyngeal Arch

Answer 22

Muscles of Mastication Temporalis Masseter Pterygoids Anterior belly of digastric Mylohyoid Tensor tympani Tensor Palatini

Question 23

Muscles of the Second Arch

Answer 23

Stapedius Stylohoid Posterior belly of digastric Auricular Muscles of facial expression

Question 24

Remnants of Meckel’s Cartilage (and how this happens)

Answer 24

Incus & Malleus: Endochondral bone formation

Question 25

Structure that arises from Pouch 1

Answer 25

Tubotympanic Recess Distal: tympanic cavity Proximal: Eustaschian tube

Question 26

Tissue that makes up clefts

Answer 26

Ectoderm

Question 27

Tissue that makes up the pouches

Answer 27

Endoderm

Question 28

To what are Neural crest cells particularly susceptible and why?

Answer 28

free radicals from alcohol and retinoic acid because they lack Super Oxide Dismutase (SOD)

Question 29

Treacher Collins Syndrome (symptoms and cause)

Answer 29

*Malformation of zygomatic bones, mandibular hypoplasia, lower eyelid colobonas, malformed external ears *Genetic + possibly due to high levels of retinoic acid

Question 30

What is most often the cause of craniofacial defects

Answer 30

Neural Crest Cells migrate incorrectly or not at all

Question 31

What is the core mesenchyme of the arches populated by?

Answer 31

Paraxial mesoderm Lateral Plate mesoderm *And each arch has its own population –> Therefore its own muscles

Question 32

What is the function of the ultimobranchial body?

Answer 32

Secretes calcitonin via C cells (thyroid cells), which regulates calcium levels in the blood by: 1) Increases calcium uptake 2) Prevents bone resorption (or favors net bone accretion)

Question 33

What structures arise from Pouch 2

Answer 33

Palatine Tonsils

Question 34

What structures arise from Pouch 3

Answer 34

Dorsal Wing: Inferior parathyroid gland Ventral Wing: Thymus

Question 35

What structures arise from Pouch 4

Answer 35

Dorsal Wing: Superior parathyroid gland

Question 36

What structures arise from Pouch 5

Answer 36

Ultimobranchial body

Question 37

When do neural crest cells begin to migrate? What controls this?

Answer 37

Weeks 4.5-5: Travel from dorsal region (forebrain, midbrain, hindbrain) down towards the pharyngeal arches *Regulated by Hox gene expression, SHH, and OTX2

Question 38

Where do the Neural Crest cells for each arch arise from?

Answer 38

Rhombomeres1 –> R1, R2, & Midbrain 2 –> R4 3 –> R6 & R7 4 & 6 –> R8

Question 39

Which arch is particularly susceptible to OTX2 regulation?

Answer 39

Arch 1

Question 40

Which pouch makes contact with the ectoderm?

Answer 40

Pouch 1: contacts the cleft #1 to form the external auditory meatus