Overview 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 Deriv. Cartilage Muscles Nerves Arteries Syndromes 1 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 earsPierre Robin syndromesmall jaw,tongue falls back into throat causing choking and difficulty breathing Pierre Robin syndrome small jaw,tongue falls back into throat causing choking and difficulty breathing 2 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 alonganterior border of sternocleidomastoid 3 Cartilage greater horn of hyoid Stylopharyngeus CN IX Common carotid, internal carotid arteries 4-6 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