questions 6

Branchial Apparatus

Topic updated on 08/29/17 3:48pm

  •  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


Qbank (3 Questions)

(M1.EB.3) A newborn male born prematurely at 33 weeks is noted to have mild dyspnea and difficulty with feeding. Examination reveals bounding peripheral radial pulses and a continuous 'machine-like' murmur. The patient is subsequently started on indomethacin. Which of the following is the embryologic origin of the structure most likely responsible for this patient's presentation? Topic Review Topic

1. 1st branchial cleft
2. 4th branchial arch
3. 4th branchial pouch
4. 6th aortic arch
5. 6th branchial pouch

(M1.EB.41) A 26-year-old female presents to your clinic with complaints of increasing muscle fatigue that worsens after periods of sustained activity. She also reports both ptosis and diplopia that make reading in the late afternoon and evenings difficult. An edrophonium test is performed and is positive, demonstrating resolution of the patient's weakness. Which of the following embryologic structures gives rise to the organ commonly affected as a complication of this patient's condition? Topic Review Topic

1. 1st branchial pouch
2. 2nd branchial cleft
3. 3rd branchial arch
4. 3rd branchial pouch
5. 4th branchial pouch

(M1.EB.42) A 47-year-old female undergoes a thyroidectomy for treatment of Graves' disease. Post-operatively, she reports a hoarse voice and difficulty speaking. You suspect that this is likely a complication of her recent surgery. What is the embryologic origin of the damaged nerve that is most likely causing this patient's hoarseness? Topic Review Topic

1. 1st pharyngeal arch
2. 2nd pharyngeal arch
3. 3rd pharyngeal arch
4. 4th pharyngeal arch
5. 6th pharyngeal arch

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