Head and Neck Development PDF

Head and neck development Dr/ Bothina zakria lecturer of human anatomy and embryology  Head and neck development The vertebrate cranial region has: A neuro-cranium associated with brain & major sense organs. A viscera-cranium, formed from the pharyngeal...

Head and neck development Dr/ Bothina zakria lecturer of human anatomy and embryology  Head and neck development The vertebrate cranial region has: A neuro-cranium associated with brain & major sense organs. A viscera-cranium, formed from the pharyngeal (branchial) arches, associated with the oral region and pharynx.  Embryonic components of the head and neck: Neural tube & ectodermal placodes form brain & special sense organ. The neural crest contributes to face, palate, tongue, pharynx, larynx, external and middle ear, and also forms intrinsic eye muscles Cranial paraxial mesoderm forms the muscles of the head, including extrinsic eye muscles Occipital somites form occipital part of skull and tongue muscles.  Pharyngeal Apparatus Pharyngeal arches (1, 2, 3, 4, and 6) composed of mesoderm and neural crest Pharyngeal pouches (1, 2, 3, 4) lined with endoderm Pharyngeal grooves or clefts (1, 2, 3, and 4) lined with  Structure & derivatives of pharyngeal arches appear during weeks 4–5 Each arch has its own artery, cranial nerve, muscles & skeletal element. face, palate, tongue, thyroid gland, pharynx, larynx, and external & middle parts of ear.  Structures Derived from Pharyngeal pouches 1st pouch gives: tubotympanic recess, tympanic membrane,tympanic cavity , mastoid antrumandpharyngotympanic tube 2nd pouch gives:tonsillar sinus or fossa ,tonsillar crypts. 3rd pouch gives: thymus. Inferior parathyroid glands. 4th pouch gives:superior parathyroid gland.  Structures Derived from Pharyngeal clefts or grooves 1st persists as the external acoustic meatus or ear canals. The other grooves lie in a slit like depression-the cervical sinus- and are normally obliterated along with the sinus as the neck develops  Development of the face Mandibular processes fuse medially, forming the lower jaw Medial and lateral nasal swellings grow and partially surround the paired nasal placodes, which deepen into two nasal cavities. These remain separated by nasal septum but are continuous with oral cavity Medial nasal swellings fuse together creating intermaxillary segment, which forms the median part of the nose, philtrum, and the primary palate  Maxillary processes fuse with lateral nasal swellings (forming side of the nose) and the nasolacrimal duct forms along this line of fusion Maxillary and mandibular processes partially fuse forming cheeks Inside oral cavity, maxillary segments project downwards, either side of the tongue, as palatal shelves which elevate and fuse together in the midline, and also with the primary palate, creating the definitive palate. The palate develops from the primary and the secondary palate.The primary palate develops from the innermost part of the intermaxillary segment. The secondary palate is formed of two shelf-like outgrowths from the maxillary swelling. In the seventh week, these shelves fuse with each other to form the secondary palate. Anteriorly, these shelves also fuse with the primary palate and cranially with the nasal septum. The incisive foramen is considered the midline landmark between the primary and secondary palate. The formation of secondary palate causes separation of primitive oral cavity into the definitive oral and nasal cavities. The definitive choanae are located at junction of nasal cavity and pharynx. If any of these fusions fail, congenital facial clefting occurs—most commonly cleft lip and palate.  Development of the skull Base of the skull (chondro-cranium) formed by the endo-chondral method of ossification Skull vault (neuro-cranium) formed by direct dermal ossification. Skull bones do not fuse together until early childhood, allowing cranium to deform during birth then expand during childhood as the brain enlarges.  Development of Thyroid Gland Thyroid gland does not develop from a pharyngeal pouch. It develops from the thyroid diverticulum, which forms from midline endoderm in floor of pharynx. The thyroid diverticulum migrates caudally to its adult anatomic position in the neck but remains connected to the foregut via the thyroglossal duct, which is later obliterated The former site of the thyroglossal duct is indicated in the adult by the foramen cecum.  Tongue development The copula is formed by the mesoderm of the second and cranial portion of the third pharyngeal arch. Large hypobranchial eminence grows rapidly and soon fuses with lateral lingual swellings along the line of demarcation, represented in the adult by the terminal sulcus of the tongue. Epiglottal swelling appears in the medial line and marks the development of the epiglottis. Immediately behind these swellings is the laryngeal orifice which is flanked by the arytenoid swellings.  Tongue innervations: 1st and 2nd pharyngeal arches form anterior 2/3(thus sensation via CN V3, taste via CN VII). 3rd and 4th pharyngeal arches form posterior1/3 (thus sensation and taste mainly via CN IX, extreme posterior via CN X). Motor innervation is via CN XII to hyoglossus (retracts and depresses tongue), genioglossus (protrudes tongue), and styloglossus (draws sides of tongue upward to create a trough for swallowing). Motor innervation is via CN X to palatoglossus (elevates posterior tongue during swallowing). Taste—CN VII, IX, X (solitary nucleus). Pain—CN V3, IX, X. Motor—CN X, XII. The Genie comes out of the lamp in style.  Common congenital anomalies First arch syndrome results from abnormal formation of pharyngeal arch 1 because of faulty migration of neural crest cells, causing facial anomalies. Two well- described syndromes are Treacher Collins syndrome and Pierre Robin sequence. Both defects involve neural crest cells. Pharyngeal fistula occurs when pouch 2 and groove 2 persist, thereby forming a fistula generally found along anterior border of muscle. Pharyngeal cyst occurs when pharyngeal grooves that are normally obliterated persist, forming a cyst usually located at angle of mandible Ectopic thyroid, parathyroid, or thymus results from abnormal migration of these glands from their embryonic position to their adult anatomic position. Ectopic thyroid tissue is found along the midline of the neck. Ectopic parathyroid or thymus tissue is generally found along the lateral aspect of the neck. Thyroglossal duct cyst or fistula occurs when parts of the thyroglossal duct persist, generally in the midline near the hyoid bone. The cyst may also be found at the base of tongue (lingual cyst). DiGeorge sequence occurs when pharyngeal pouches 3 and 4 fail to differentiate into the parathyroid glands and thymus. Neural crest cells are involved anomalies: Branchial fistula. Tongue defects (aglossia, tongue tie). 3- Facial clefts. Cleft palate.