Block 4 Embryo

Front 1

when do the pharyngeal arches appear?

Back 1

5th week

Front 2

what are the pharyngeal arches made of?

Back 2

outside ectoderm forming the clefts

core mesenchyme bar with some neural crest cells - end up making the bones. Beginnings of Nerve artery and cartilage in each bar of mesenchyme.

inside a layer of endoderm forming the pouches

Front 3

1st arch

Back 3

CN V - mastication muscles: temporalis, masseter, pterygoids

bone: mandible, maxilla, malleus incus.

Front 4

1st pouch

Back 4

The stalk-like diverticulum (turbotympanic recess) comes into contact with the first cleft (1st cleft=the external auditory canal). Distally it widens and the primitive tympanic cavity = middle ear cavity forms. Proximally it stays narrow and forms the eustachian tube.

Front 5

1st cleft

Back 5

from the other side of the turbotympanic recess from the pouch, comes this cleft. it forms the external auditory meatus.

Front 6

2nd arch

Back 6

CN VII - "seven"
stapedius
stylohyoid
muscles of facial expression
styloid process
stapes
lesser horn and upper part of hyoid

Front 7

2nd pouch

Back 7

palatine tonsil promordium but is invaded later by the lymphatic cells.
remnant: tonsilar fossa;

Front 8

3rd arch

Back 8

CN XI, stylopharyngeus;
lower part of hyoid bone

Front 9

3rd pouch

Back 9

inferior parathyroid and thymus (ventral)

Front 10

4th arch + 6th arch

Back 10

4th thyroid cartilage, cuneiform cartilage, cricoid, arytenoid;

CN X:
cricothyroid, levator palatini, constrictors of the pharynx

6th arch: recurrent laryngeal branch of the vagus

Front 11

4th pouch

Back 11

superior parathyroid and the ultimobranchial body - parafollicular cells C-cells of the thyroid

Front 12

most common branchial cleft sinus

Back 12

2nd cleft. orifice on anterior border of SCM, travels through carotid bifurcation to tonsillar fossa
(3rd would be lateral to the carotid, but it's rare)

Front 13

origin of the tongue

Back 13

1st arch forms median tongue bud (tuberculum impar) then the lateral lingual swelling – becomes the anterior 2/3 of the tongue
2nd (3rd????) arch forms midline swelling called the copula
Copula is “overtaken” by midline swellings from the 3rd and 4th arch called the hypopharyngeal eminence = posterior 1/3 of tongue

Front 14

only organ innervated by 5 CN

Back 14

V, VII, IX, X, XII

Front 15

face development

Back 15

4th week: center of the face is formed by the stomodeum, surrounded by the first pharyngeal arch

Front 16

area under the nose

Back 16

philtrum