week 1 embryology

Question 1

when do the Pharyngeal Arches develop in the embryo? what do thePharyngeal Arches lead to the development of in humans?

Answer 1

Arch 1 → Day 22
Arches 2 and 3 → Day 24
Arches 4 and 6 → Day 29

in humans contribute to much of the face and neck

Question 2

what does each arch consist of?

Answer 2

Core of mesenchyme derived from paraxial and lateral plate mesoderm → musculature of face and neck

Neural crest cells → skeletal components of face

Cranial nerve component

Artery (Aortic arches – see Embryology of Heart and Great Vessels lecture CVS block))

Question 3

how are the arches separated?

Answer 3

Externally separated by deep pharyngeal clefts
=Ectoderm lining

Internally separated by pharyngeal pouches
=Endoderm lining

Question 4

what nerves are associated with which Pharyngeal Arches?

Answer 4

1 - CNV1, 2, 3

2- CNVII

3-CNIX

4-6:-CNX (arch 4 - superir laryngeal branch, arch 6-recurrent laryngeal branch)

Question 5

what does the 1st arch contain?

Answer 5

skeletal components:
-Maxillary process (dorsal portion)
Maxilla, zygomatic and part of temporal bone
-Mandibular process (ventral portion)
Contains Meckel’s cartilage → incus, malleus and mandible

muscles: Muscles of MASTICATION, anterior belly of digastric, MYLOHYOID, tensor tympani and tensor palatini
All supplied by V3

nerve: sensory supply to skin of face, V1,2+3

Question 6

what does the 2nd arch contain?

Answer 6

skeletal components:

• Stapes, styloid process of temporal bone + stylohyoid ligament
• Lesser horn and upper part of body of hyoid

muscles:Muscles of FACIAL EXPRESSION, stapedius, stylohyoid, posterior belly of digastric, and auricular muscles

all supplies by CNVII

Question 7

what does the 3rd arch contain?

Answer 7

Greater horn and lower part of body of hyoid

Muscles of Arch 3:
Stylopharyngeus mm.

Glossopharyngeal (IX) nerve

Question 8

4th and 6th arches contain?

Answer 8

Laryngeal cartilages

Muscles of Arch 4:
Cricothyroid, levator palatini and pharyngeal constrictors
Supplied by Vagus (X) Superior laryngeal; pharyngeal plexus

Muscles of Arch 6:
Intrinsic laryngeal mm.
Supplied by Recurrent laryngeal nerve (X)

Question 9

what arises from pharyngeal clefts?

Answer 9

1st Cleft:External auditory meatus

2nd – 4th Clefts:
lose contact with outside and form the cervical sinus (usually disappears)

Question 10

what arises from pharyngeal pouches?

Answer 10

1st Pouch= middle ear, eustachian tube, tympanic membrane

2nd Pouch=palatine tonsil

3rd Pouch= Inferior parathyroid gland, Thymus

4th Pouch = Superior parathyroid gland, Ultimobranchial body (C cells of thyroid gland)

Question 11

how does the ear develop?

Answer 11

Otic Placodes becomes Otic Vesicles becomes inner ear