•  Branchial apparatus (pharyngeal apparatus)
    • branchial clefts (branchial grooves)
      • derived from ectoderm located between the arches
    • branchial arches
      • derived from mesoderm (muscles, arteries) and neural crest cells (bones, cartilage)
      • each arch is associated with a cranial nerve
    • branchial pouches
      • derived from endoderm which line the foregut
Branchial arch innervation
  • 1st arch derivatives
    • CN V2 and V3: muscles for "chewing"
  • 2nd arch derivatives
    • CN VII: muscles for "facial expression"
  • 3rd arch derivatives
    • CN IX
  • 4th and 6th arch derivatives 
    • supplied by CN X: muscles for  "swallowing" and "speaking"
  • CN V3, VII, IX, and X are both sensory and motor. 
  • CN V2 is only sensory
Branchial arch derivatives
  • Meckel's cartilage
    • mandible
    • malleus
    • incus
    • sphenomandibular ligament
  • Muscles of mastication
    • temporalis
    • masseter
    • lateral and medial pterygoids
  • Mylohyoid
  • Anterior belly of digastric
  • Tensor tympani
  • Tensor veli palatini
  • Anterior 2/3 of tongue
CN V2 and V3 Maxillary artery, external carotid artery
  • Treacher Collins syndrome 
    • neural crest cells fail to migrate into arch 1
    • results in underdeveloped zygomatic bones, mandibular hypoplasia, lower eyelid colobomas, and malformed ears
  • Pierre Robin syndrome
    • small jaw, tongue falls back into throat causing choking and difficulty breathing
  • Reichert's cartilage
    • stapes
    • styloid process
    • lesser horn of hyoid
    • stylohyoid ligament
  • Muscles of facial expression
  • stapedius
  • stylohyoid
  • posterior belly of digastric
CN VII Stapedial artery, hyoid artery
  • Congenital pharyngocutaneous fistula 
    • persistence of cleft and pouch
    • fistula between internal tonsillar area and external neck
    • found along anterior border of sternocleidomastoid
  • Cartilage
    • greater horn of hyoid
  • Stylopharyngeus
CN IX Common carotid, internal carotid arteries  
  • Cartilages
    • thyroid
    • cricoid
    • arytenoids
    • corniculate
    • cuneiform
4th arch
  • pharyngeal constrictors except stylopharyngeus
  • cricothyroid
  • muscles of soft palate except tensor veli palatini

6th arch

  • intrinsic muscles of larynx except cricothyroid
  • upper muscles of esophagus
4th arch

CN X: superior laryngeal branch (swallowing)

6th arch

CN X: recurrent laryngeal branch (speaking)

4 - Right: subclavian artery; Left: aortic arch

6 - Right: pulmonary artery; Left: pulomonary artery & ductus arteriosus 



Branchial cleft derivatives
  • 1st cleft
    • develops into epithelial lining of external auditory meatus
  • 2nd - 4th cleft
    • forms temporary cervical sinuses
    • later obliterated by proliferation of 2nd arch
  • Persistent cervical sinus
    • branchial cleft cyst within lateral neck/angle of mandible
Branchial pouch derivatives
  • 1st pouch 
    • forms
      •  epithelial (endoderm derived) lining of middle ear cavity and eustachian tube
      • mastoid air cells
  • 2nd pouch
    • forms epithelial lining of palatine tonsil
  • 3rd pouch
    • dorsal wings
      • forms inferior parathyroids
    • ventral wings
      • forms thymus 
    • 3rd pouch derivatives end up below the 4th derivatives
  • 4th pouch dorsal wings
    • forms superior parathyroids 
  • DiGeorge syndrome (22q11 deletion)
    • 3rd and 4th pouches fail to differentiate into thymus and parathyroid glands
    • Symptoms
      • ↓ PTH due to parathyroid aplasia
        • tetany due to hypocalcemia
      • T cell deficiency due to thymic aplasia
        • recurrent viral/fungal infections
        • cell mediated immunity still functional and can fight bacterial infections
      • congenital heart and great vessel defects
      • absent thymic shadow on CXR
  • MEN 2A
    • mutation of germline RET (neural crest cells)
      • pheochromocytoma
      • parathyroid tumor
        • derived from 3rd/4th pharyngeal pouch
      • medullary thyroid cancer
        • derived from parafollicular cells from the 4th/5th pharyngeal pouch 
        • NOTE: 5th pouch degenerates during development

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