Pharyngeal arches

Question 1

pharyngeal clefts

Answer 1

1. External invagination of ectoderm.

2. 4 clefts

Question 2

pharyngeal arches

Answer 2

1. Core of mesenchyme (neural crest and paraxial mesoderm). (leaves week 5)
2. Neural crest will give rise to ct components; paraxial mesoderm gives rise to muscles.
3. Each arch has its own nerve (cranial nerve) and blood supply (aortic arch artery).
4. 6 pharyngeal arches initially develop; but the 5th regresses, leaving arches 1-4 and 6.

Question 3

pharyngeal pouches

Answer 3

1. Internal evagination of pharyngeal endoderm.

2. 4 pouches

Question 4

skeletal derivatives of arch 1

Answer 4

viscerocranium (malleus, incus) and connective tissues of face

Question 5

muscular derivatives of arch 1

Answer 5

a. Muscles of mastication (temporalis, masseter, medial and lateral pterygoids)
b. Also: anterior belly of digastric, mylohyoid, tensor tympani, tensor veli palatini

Question 6

nerve of arch 1

Answer 6

trigeminal CN V(3)

Question 7

oropharyngeal membrane

Answer 7

Oropharyngeal membrane develops between the two processes of first arch.

a. Composed of an outer layer of ectoderm and an inner layer of endoderm.
b. Ruptures by day 26 to allow communication between pharynx and oral cavity.

Question 8

which arch is the largest

Answer 8

1 it forms entire face

Question 9

skeletal derivatives arch 2

Answer 9

a. Stapes, styloid process of temporal bone

b. Stylohyoid ligament; lesser horn and superior portion of body of hyoid

Question 10

muscular derivatives arch 2

Answer 10

a. Muscles of facial expression

b. Also: stylohyoid, posterior belly of digastric, stapedius

Question 11

arch 2 nerve

Answer 11

facial nerve CN vII

Question 12

arch 3 deriatives skeletal

Answer 12

1. Skeletal derivatives: greater horn and inferior portion of body of hyoid bone.

Question 13

arch 4 skeletal

Answer 13

with 6th arch, forms all laryngeal cartilages.

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Question 14

arch 5

Answer 14

regresses

Question 15

arch 6 skeletal

Answer 15

with 4th arch, forms all laryngeal cartilages.

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Question 16

pouch 1 derivatives

Answer 16

formation of middle ear and auditory lobe

Question 17

pouches are

Answer 17

evaginations of the endoderm…

Question 18

pouch 2 forms

Answer 18

stroma of palatine tonsil, tonsillar fossa

Question 19

pouch 3

Answer 19

1. Dorsal portion: inferior parathyroid glands

2. Ventral portion: thymus

Question 20

pouch 4

Answer 20

1. Dorsal portion: superior parathyroid glands

2. Ventral portion: ultimobranchial body (see development of thyroid gland below

Question 21

first cleft derivative

Answer 21

external ear

Question 22

second arch overgrows

Answer 22

arches 3 and 4, burying clefts 2-4

Question 23

remnants of clefts 2-4 form

Answer 23

cervial sinus which is later obliterated

Question 24

thyroid gland development

Answer 24

A. Derived from a median endodermal thickening of pharyngeal floor.
B. The gland descends along the pharynx into the neck, remaining connected to tongue via the thyroglossal duct (degenerates by week 7).
C. Superior opening of the thyoglossal duct remains as the foramen cecum.
D. In about 50% of individuals a pyramidal lobe of the thyroid is present; this is a remnant of the distal thyroglossal duct.
E. Parafollicular (C cells) are derived from the ultimobranchial body of the 4th pouch.

Question 25

pyramidal lobe

Answer 25

thyroid tissue in neck, thryroglossal cyst...

Question 26

tongue development

Answer 26

A. 1st pharyngeal arch form the body (anterior 2/3) of tongue (GSA from trigeminal n.) B. 3rd arch forms the root (posterior 1/3) of tongue (GVA from glossopharyngeal n.) C. 4th arch forms the epiglottic region of tongue (GVA from vagus n.) D. Muscle derived from paraxial mesoderm of occipital somites

Question 27

1st pharyngeal arch is....the rest are...

Answer 27

ectoderm, endoderm

Question 28

gsa is

Answer 28

ectoderm

Question 29

gva is

Answer 29

endoderm

Question 30

ectopic thyroid or parathyroid tissue

Answer 30

1. Remnants of thyroid tissue can remain along the course of migration. 2. The parathyroids also undergo a migration and are highly variable in their location. foramend cecum through tongue

Question 31

lateral cervical cysts

Answer 31

form when the cervical sinus fails to degenerate. These cysts are found along the anterior border of the SCM

Question 32

branchial fistula

Answer 32

occur when second arch fails to overgrow the third and fourth arches. The cervical sinus retains a connection with the surface (external fistula). In rare cases, the lateral cervical cyst can open into the pharynx (internal fistula).

Question 33

thyroglossal cyst

Answer 33

1. Remnant of thyroglossal duct. | 2. Always located on or near midline of the neck.

Question 34

neural crest defects

Answer 34

1. Neural crest cells are important for the development of the pharyngeal arches. 2. Severe craniofacial defects result from disruption of neural crest cell migration or differentiation. 3. Ex: Treacher Collins Syndrome, Robin Sequence, DiGeorge Anomaly

Question 35

digeorge syndrom

Answer 35

a. Deletion on long arm of Chromosome 22 b. Cardiac abnormalities c. Craniofacial defects d. Thymic hypoplasia e. Parathyroid dysfunction – hypocalcemia due to parathyroid insufficiencies

Question 36

stomodeum

Answer 36

invagination of ectoderm which will form oral cavity

Question 37

sve

Answer 37

motor innervation to hpayngeal arch muscle

Question 38

ultimobranchial body

Answer 38

migrates into parafollicular cells

Question 39

foramen cecum

Answer 39

where oropharyngeal membrande whould have attached demarcates where thyroid gland originally formed

Question 40

lateral cervical cysts are also called

Answer 40

branchial cysts

Question 41

treacher collin

Answer 41

-Malar hypoplasia -Micrognathia -Malformed external ear -impaired hearing

Question 42

robin sequence

Answer 42

Micrognathia - Cleft palate - Glossoptosis

Question 43

catch 22

Answer 43

-Chromosome 22 -Cardiac defects -Abnormal facies -Thymic aplasia -Cleft palate -Hypocalcemia (parathyroid deficiency)

Question 44

goldenhar syndrom

Answer 44

``` -Underdeveloped facial bones -Ear anomalies -Eye anomalies -hemivertebrae -spina bifida ```

Question 45

muscle derivatives of arch 3

Answer 45

stylopharyngeus

Question 46

arch 3 merve

Answer 46

3. Nerve: glossopharyngeal nerve (CN IX

Question 47

arch 4 muscle

Answer 47

2. Muscular derivatives: muscles of pharynx; cricothyroid(larynx muscle) (except stylopharyngeus

Question 48

arch 4 nerve

Answer 48

3. Nerve: vagus nerve (CN X)

Question 49

arch 6 muscle

Answer 49

2. Muscular derivatives: laryngeal muscles (except cricothyroid); skeletal muscle of esophagus

Question 50

arch 6 nerve

Answer 50

3. Nerve: vagus nerve (CN X; recurrent laryngeal nerve